- A homochiral microporous hydrogen-bonded organic framework for highly enantioselective separation of secondary alcohols
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A homochiral microporous hydrogen-bonded organic framework (HOF-2) based on a BINOL derivative has been synthesized and structurally characterized to be a uninodal 6-connected {3355667} network. This new HOF exhibits not only a permanent porosity with the BET of 237.6 m 2 g-1 but also, more importantly, a highly enantioselective separation of chiral secondary alcohols with ee value up to 92% for 1-phenylethanol.
- Li, Peng,He, Yabing,Guang, Jie,Weng, Linghong,Zhao, John Cong-Gui,Xiang, Shengchang,Chen, Banglin
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- Construction of pincer-type symmetrical ruthenium(II) complexes bearing pyridyl-2,6-pyrazolyl arms: Catalytic behavior in transfer hydrogenation of ketones
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Convenient synthesis of four new distorted octahedral ruthenium(II) complexes (1, 2, 3, 4) having general molecular formula [RuCl2LPAr3] (L = pyridine-based tridentate ligands not containing N-H bonds) is described. Their composition and structure were determined by elemental analysis and NMR spectra, and complexes 2 and 4 were also identified by X-ray single-crystal diffraction. All ruthenium(II) complexes exhibited good to excellent catalytic activity in the transfer hydrogenation of ketones. Among them, complex 4 achieved the highest final TOF value of 51600 h-1 for a high molar ratio of substrate to catalyst (2000:1).
- Zhu, Zhu,Zhang, Jie,Fu, Haiyan,Yuan, Maolin,Zheng, Xueli,Chen, Hua,Li, Ruixiang
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- Iron(II) complexes for the efficient catalytic asymmetric transfer hydrogenation of ketones
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Iron(II) carbonyl compounds of the type trans-[Fe(NCMe)(CO)(P-N-N-P)] [BF4]2 bearing the ethylenediamine-derived diiminodiphosphine ligands (R,R)- or (5,5)-1,2-diphenyl-1,2-diaminoethane were synthesized and characterized, including by their crystal structures. The new complexes are suitable precatalysts for the transfer hydrogenation of ketones at room temperature, giving turnover frequencies of up to 2600 h-1 with low catalyst loadings (0.025-0.17%). Screening experiments showed that the precatalysts are able to produce alcohols from a wide range of simple ketones. For sterically demanding prochiral ketones, excellent enantioselectivities were obtained (up to 96% ee).
- Meyer, Nils,Lough, Alan J.,Morris, Robert H.
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- Ruthenium(II) Complexes of 4′-(Aryl)-2,2′:6′,2′′-terpyridyl Ligands as Simple Catalysts for the Transfer Hydrogenation of Ketones
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A series of cationic [Ru(L)(PPh3)2Cl]+ (1–3) and neutral [Ru(L)(PPh3)Cl2] (4–6) RuII complexes were synthesized by reacting [RuCl2(PPh3)2] with 4′-(aryl)-2,2′:6′,2′′-terpyridyl-based ligands (L1–L3) with various aryl groups (tolyl, phenyl and 4-fluorophenyl). The synthesized RuII complexes were unambiguously characterized by various spectroscopic techniques such as FTIR and multinuclear NMR spectroscopy as well as HRMS. The neutral complexes (4–6) were also structurally characterized by single-crystal X-ray diffraction studies. Photophysical and electrochemical studies of the RuII complexes were performed to elucidate the effects of the 4′-aryl substituents of L1–L3. These RuII complexes show good catalytic activities in the transfer hydrogenation (TH) of ketones with a wide substrates scope in 2-propanol under reflux. An optimization study revealed that the neutral RuII complexes are better catalysts than the cationic RuII complexes for TH reactions. Finally, [Ru(L1)(PPh3)2H]+ (7) with a [RuII–H] functionality was successfully synthesized and isolated and is proposed as the catalytically active species. A control experiment with the [RuII–H] complex in the absence of base was performed to establish the mechanism for the catalytic TH of ketones.
- Maity, Apurba,Sil, Amit,Patra, Sanjib K.
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- Novel chiral tetraaza ligands: synthesis and application in asymmetric transfer hydrogenation of ketones
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Novel chiral tetraaza ligands, N1,N2-bis(2-(piperidin-1-yl)benzylidene)cyclohexane-1,2-diamine 1 and N1,N2-bis(2-(piperidin-1-yl)benzyl)cyclohexane-1,2-diamine 2, have been synthesized and fully characterized by
- Shen, Wei-Yi,Zhang, Hui,Zhang, Hua-Lin,Gao, Jing-Xing
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- Room-temperature Ru(II)-catalyzed transfer hydrogenation of ketones and aldehydes in air
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Transfer hydrogenation (TH) of ketones and aldehydes was efficiently carried out in 2-propanol at room temperature by means of a ruthenium(II) complex catalyst bearing a 2-(benzoimidazol-2-yl)-6-(pyrazol-1-yl)pyridine ligand. TH of the ketone substrates proceeded in air, reaching final TOFs of up to 59,400 h-1, and the reduction of aldehydes proceeded under a nitrogen atmosphere to achieve final TOFs of up to 5940 h-1.
- Zhao, Miao,Yu, Zhengkun,Yan, Shenggang,Li, Yang
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- Dimeric Ruthenium(II)-NNN Complex Catalysts Bearing a Pyrazolyl-Pyridylamino-Pyridine Ligand for Transfer Hydrogenation of Ketones and Acceptorless Dehydrogenation of Alcohols
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Dimeric pincer-type ruthenium(II)-NNN complexes bearing an unsymmetrical pyrazolyl-pyridylamino-pyridine ligand were prepared and characterized by NMR, elemental analysis, and X-ray single crystal structural determination. These complexes exhibited very high catalytic activity for both transfer hydrogenation of ketones and acceptorless dehydrogenation of secondary alcohols, achieving TOF values up to 1.9 × 106 h-1 in the transfer hydrogenation of ketones. The high catalytic activity of the Ru(II) complex catalysts is attributed to the presence of the unprotected NH functionality in the ligand and hemilabile unsymmetrical coordination environment around the central metal atoms in the complex.
- Wang, Qingfu,Chai, Huining,Yu, Zhengkun
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- Assembled Multinuclear Ruthenium(II)-NNNN Complexes: Synthesis, Catalytic Properties, and DFT Calculations
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Using a coordinatively unsaturated 16-electron mononuclear ruthenium(II)-pyrazolyl-imidazolyl-pyridine complex [Ru(II)-NNN] as the building block and oligopyridines as the polydentate ligands, pincer-type tri- A nd hexanuclear ruthenium(II) complexes [Ru(II)-NNNN]n were efficiently assembled. These complexes were characterized by elemental analyses, NMR, IR, and MALDI-TOF mass spectroscopies. In refluxing 2-propanol, the multinuclear ruthenium(II)-NNNN complexes exhibited exceptionally high catalytic activity for the transfer hydrogenation of ketones at very low concentrations and reached turnover frequencies (TOFs) up to 7.1 × 106 h-1, featuring a remarkable cooperative effect from the multiple Ru(II)-NNNN functionalities. DFT calculations have revealed the origin of the high catalytic activities of these Ru(II)-NNNN complexes.
- Liu, Tingting,Wu, Kaikai,Wang, Liandi,Fan, Hongjun,Zhou, Yong-Gui,Yu, Zhengkun
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- A family of novel cationic ruthenium pincer complexes: Synthesis, characterization and catalytic activity in the transfer hydrogenation of ketones
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A family of novel cationic ruthenium complexes [RuHL(PAr3) 2]Cl (Ar = phenyl, p-methoxyphenyl, and p-trifluoromethylphenyl; L = 2,6-bis(1,5-diphenyl-1H-pyrazol-3-yl)pyridine) has been synthesized and characterized by IR, 31P{1H} NMR, 1H NMR and elemental analyses. The [RuHL(PPh3)2]Cl was further identified by X-ray crystallography. These complexes exhibit good to excellent catalytic activities for the transfer hydrogenation of ketones in refluxing 2-propanol, and the highest TOF is up to 3534 h- 1. The effect of electronic factors of these complexes on the transfer hydrogenation of ketones reveals that the catalytic activity is promoted by the electron-withdrawing phosphine.
- Wang, Lei,Pan, Hai-Ran,Yang, Qin,Fu, Hai-Yan,Chen, Hua,Li, Rui-Xiang
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- Aza-crown compounds synthesised by the self-condensation of 2-amino-benzyl alcohol over a pincer ruthenium catalyst and applied in the transfer hydrogenation of ketones
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A well-defined PNN-Ru catalyst was revisited to self-condense 2-aminobenzyl alcohol in forming a series of novel aza-crown compounds [aza-12-crown-3 (1), aza-16-crown-4 (2) and aza-20-crown-5 (3)]. All aza-crown compounds are separated and determined by NMR, IR, and ESI-MS spectroscopy as well as X-ray crystallography, indicating the saddle structure of 1 and the twisted 1,3-alternate conformation structure of 3. These aza-crown compounds have been explored to study ferric initiation of transfer hydrogenation (TH) of ketones into their corresponding secondary alcohols in the presence of 2-propanol with a basic t-BuOK solution, achieving a high conversion (up to 95%) by a ferric complex with 2 in a low loading (0.05 mol%). This journal is
- Zhang, Shanshan,Wang, Zheng,Cao, Qianrong,Yue, Erlin,Liu, Qingbin,Ma, Yanping,Liang, Tongling,Sun, Wen-Hua
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- Asymmetric Transfer Hydrogenation of Ketones with Well-Defined Manganese(I) PNN and PNNP Complexes
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Three new manganese complexes trans-[Mn(P-NH-NH-P)(CO)2][Br], (14) P-NH-NH-P = (S,S)-PPh2CH2CH2NH-CHPhCHPhNHCH2CH2PPh2), fac-[Mn(P′-NH-NH2)(CO)3][Br], (15) P′-NH-NH2 = (S,S)-PPh2(C6H4)NHCHPhCHPhNH2, and syn-mer-Mn(P-NH-NH2)(CO)2Br, (16) P-NH-NH2 = (S,S)-PPh2CH2CH2NHCHPhCHPhNH2 were synthesized and tested for the asymmetric transfer hydrogenation (ATH) of acetophenone in 2-PrOH. The ligands have stereogenic centers derived from the starting diamine, (S,S)-DPEN. Complex 16 was shown by NOE NMR experiments to have Mn-Br syn to the N-H of the secondary amine. Only the precatalyst 16, upon reaction with potassium tert-butoxide (KOtBu) in 2-PrOH, generated an active system at 80 °C for the ATH of acetophenone to 1-phenylethanol in an enantiomeric excess (ee) of 42% and thus was selected for further investigation into the mechanism of transfer hydrogenation. The corresponding amido complex Mn(P-N-NH2)(CO)2 (17), a borohydride complex syn-mer-Mn(P-NH-NH2)(CO)2(BH4) (18), and an ethoxide complex anti-mer-Mn(P-NH-NH2)(CO)2(OEt) (19′) were independently synthesized and tested in the ATH of acetophenone. The amido complex 17 and the borohydride complex 18 displayed similar activity to 16 activated in basic 2-PrOH, but the anti NH OEt complex 19′ was completely inactive. This result suggested that the NH effect, as described by Noyori, was required to obtain catalytic activity. The syn NH BH4 manganese complex is one of the most active manganese ATH catalysts to date and can hydrogenate a variety of aromatic ketones, including base-sensitive substrates such as p-acetylbenzoate ethyl ester.
- Demmans, Karl Z.,Olson, Maxwell E.,Morris, Robert H.
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- Samarium-induced convenient reductive dimerization of aromatic ketones in aqueous methanol: A mechanistic approach
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Samarium metal has been used for the reductive dimerization of aromatic ketones in the presence of additives; the most probable mechanism has been advanced to explain the diastereoselectivity of this dimerization reaction.
- Banik, Bimal K.,Banik, Indrani,Aounallah, Nacer,Castillo, Mark
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- Synthesis of ruthenium (II) complexes containing a dihydroperimidine- derived phosphine ligand and their application in transfer hydrogenation of ketones
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The new ruthenium (II) phosphine complexes (η6-C 6H6)RuCl2[μ- (PPh2CH 2N)2CH2(C10H6)]RuCl 2(η6-C6H6) (1) and RuCl 2(PPh3)[(PPh2CH2N) 2CH2(C10H6)] (2) were synthesized and characterized by 1H NMR, 31P {1H} NMR and elemental analysis. Moreover, the structure of ruthenium (II) phosphine complex 1 was confirmed by X-ray crystallography. With complex 1 as the catalyst, the transfer hydrogenation of ketones reacted well, affording the corresponding alcohols in good yields under mild conditions.
- Fu, Qi,Zhang, Lei,Yi, Tao,Zou, Mingjun,Wang, Xiaoyan,Fu, Haiyan,Li, Ruixiang,Chen, Hua
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- Applications of ruthenium hydride borohydride complexes containing phosphinite and diamine ligands to asymmetric catalytic reactions
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(Chemical Equation Presented) A series of novel trans-ruthenium hydride borohydride complexes with chiral phosphinite and diamine ligands were synthesized. They can be used in the asymmetric transfer hydrogenation of aryl ketones, including base-sensitive
- Guo, Rongwei,Chen, Xuanhua,Elpelt, Christian,Song, Datong,Morris, Robert H.
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- Enantioselective borane reduction of aromatic ketones using chiral BINOL derivatives as ligands in an aluminum catalyst
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Chiral aluminum complex-catalyzed asymmetric borane reduction of aromatic ketones has been successfully carried out in the presence of (R)-BINOL derivatives as ligands. Secondary alcohols were obtained in high yields with good enantioselectivities (up to 90% e.e.).
- Lin, Yang-Miin,Fu, I-Pin,Uang, Biing-Jiun
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- Ruthenium(II) complex catalysts bearing a 2,6-bis(tetrazolyl)pyridine ligand for the transfer hydrogenation of ketones
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Three ruthenium(II) complex catalysts bearing 2,6-bis(tetrazolyl)pyridine were synthesized, structurally characterized, and applied in the transfer hydrogenation of ketones. Their different catalytic activities were attributed to the different phosphine ligands on the 4-chloro-2,6-bis(1-(p-tolyl)- 1H- tetrazol-5-yl)pyridine ruthenium(II) complexes, with that based on 1,4- bis(diphenylphosphino) butane exhibiting better catalytic activity. A variety of ketones were reduced to their corresponding alcohols with >95% conversion.
- Wang, Liandi,Liu, Tingting
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- Enantioselective reduction of acetophenone analogues using carrot and celeriac enzymes system
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The enantioselective reduction of acetophenone analogues catalyzed by carrot and celeriac was performed in moderate conversions and excellent enantiomeric excesses. The steric factors and electronic effects of the substituents at the aromatic ring were found to significantly affect the efficiency of the enantioselective reduction of acetophenone analogues, while they had a little effect on the enantioselectivity of acetophenone analogues reduction. It was also found that the conversions of acetophenone analogues reduction at 33 °C by means of both biocatalysts were three times as great as those at room temperature.
- Liu, Xiang,Pan, Zheng Guang,Xu, Jian He,Li, He Xing
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- Reverse micellar aggregates: Effect on ketone reduction. 1. Substrate role
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The reduction of three aromatic ketones, acetophenone (AF), 4-methoxyacetophenone (MAF), and 3-chloroacetophenone (CAF), by NaBH4 was followed by UV-vis spectroscopy in reverse micellar systems of water/AOT/isooctane at 25.0 °C (AOT is sodium 1,4-bis-2- ethylhexylsulfosuccinate). The first-order rate constants, kobs, increase with the concentration of surfactant due to the substrate incorporation at the reverse micelle interface, where the reaction occurs. For all the ketones the reactivity is lower at the micellar interface than in water, probably reflecting the low affinity of the anionic interface for BH 4-. Kinetic profiles upon water addition show maxima in kobs at W0 ≈ 5 probably reflecting a strong interaction between water and the ionic headgroup of AOT; at W0 0 BH4- is repelled from the anionic interface once the water pool forms. The order of reactivity was CAF ? AF > MAF. Application of a kinetic model based on the pseudophase formalism, which considers distribution of the ketones between the continuous medium and the interface, and assumes that reaction take place only at the interface, gives values of the rate constants at the interface of the reverse micellar system. At W0 = 5, we conclude that NaBH4 is wholly at the interface, and at W0 = 10 and 15, where there are free water molecules, the partitioning between the interface and the water pool has to be considered. The results were used to estimate the ketone and borohydride distribution constants between the different pseudophases as well as the second-order reaction rate constant at the micellar interface.
- Correa, N. Mariano,Zorzan, Daniel H.,Chiarini, Marco,Cerichelli, Giorgio
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- Reverse micellar aggregates: Effect on ketone reduction. 2. Surfactant role
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Kinetics of the reduction of 3-chloroacetophenone (CAF) with sodium borohydride (NaBH4) were followed by UV-vis spectroscopy at 27.0 °C in different reverse micellar media, toluene/BHDC/ water and toluene/AOT/water, and compared with results in an isooctane/AOT/water reverse micellar system. AOT is sodium 1,4-bis-2-ethylhexylsulfosuccinate, and BHDC is benzyl-n-hexadecyl dimethylammonium chloride. The kinetic profiles were investigated as a function of variables such as surfactant and NaBH4 concentration and the amount of water dispersed in the reverse micelles, W 0 = [H2O]/[surfactant]. In all cases, the first-order rate constant, kobs, increases with the concentration of surfactant as a consequence of incorporating the substrate into the interface of the reverse micelles where the reaction takes place. The reaction is faster at the cationic interface than at the anionic one probably because the negative ion BH 4- is part of the cationic interface. The effect of the external solvent on the reaction shows that reduction is favored in the isooctane/ AOT/water reverse micellar system than that with an aromatic solvent. This is probably due to BH4- being more in the water pool of the toluene/AOT/water reverse micellar system. The kinetic profile upon water addition depends largely on the type of interface. In the BHDC system, kobs increases with W0 in the whole range studied while in AOT the kinetic profile has a maximum at W0 ~5, probably reflecting the fact that BH4- is part of the cationic interface while, in the anionic one, there is a strong interaction between water and the polar headgroup of AOT below W0 = 5 and, above that, BH 4- is repelled from the interface once the water pool has formed. Application of a kinetic model based on the pseudophase formalism, which considers the distribution of the ketone between the continuous medium and the interface and assumes that reaction takes place only at the interface, has enabled us to estimate rate constants at the interface of the reverse micellar systems. At W0 4 is wholly at the interface and, at W0 ≥ 10, where there are free water molecules, also the partitioning between the interface and the water pool was taken into account. The results were used to evaluate CAF and NaBH 4 distribution constants between the different pseudophases as well as the second-order reaction rate constant of the reduction reaction in the micellar interface.
- Correa, N. Mariano,Zorzan, Daniel H.,D'Anteo, Loredana,Lasta, Ermanno,Chiarini, Marco,Cerichelli, Giorgio
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- Substituent Effect on the Catalytic Activity of Ruthenium(II) Complexes Bearing a Pyridyl-Supported Pyrazolyl-Imidazolyl Ligand for Transfer Hydrogenation of Ketones
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Air- and moisture-stable ruthenium(II) complexes bearing a multisubstituted pyrazolyl-imidazolyl-pyridine ligand were synthesized and structurally characterized by NMR and X-ray single-crystal crystallographic analyses. The substituents on the imidazolyl moiety of the NNN ligand exhibited a remarkable impact on the catalytic activity of the corresponding Ru(II) complexes for transfer hydrogenation of ketones in refluxing 2-propanol, following the order NHTs > Me > H > NO2, to tune the catalytic activity. The highest final TOF value of 345 600 h-1 was reached by means of 0.05 mol % of the Ru(II)-NHTs-substituted NNN complex as the catalyst. The corresponding structurally confirmed RuH complexes are proposed as the catalytically active species.
- Chai, Huining,Liu, Tingting,Wang, Qingfu,Yu, Zhengkun
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- A pH-Responsive Soluble-Polymer-Based Homogeneous Ruthenium Catalyst for Highly Efficient Asymmetric Transfer Hydrogenation (ATH)
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A pH-responsive polymer has been synthesized successfully by means of copolymerization of dimethyl aminopropyl acrylamide (DMAPA) and N-p-styrenesulfonyl-1,2-diphenylethylenediamine (V-TsDPEN). The pH-responsive polymer coordination ruthenium complex was thus prepared and employed as an efficient catalyst for the asymmetric transfer hydrogenation (ATH) of various ketones. The polymer catalyst exhibited an attractive pH-induced phase-separable behavior in water: it could be dissolved in water when the pH of the solution was lower than 6.5 at the beginning of the reaction, but was precipitated completely from water when the pH of the solution was above 8.5 after reaction. Additionally, the catalysts were highly efficient for the ATH of a wide range of substrates that bore different functional groups and could be recycled easily from the aqueous solution by means of self-separation. They could be recycled eight times without significant changes in catalytic activity and enantioselectivity.
- Xie, Yinzheng,Wang, Mengpan,Wu, Xiaohui,Chen, Chen,Ma, Wenbo,Dong, Qifeng,Yuan, Mingming,Hou, Zhenshan
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- Ionic and Neutral Half-Sandwich Guanidinatoruthenium(II) Complexes and Their Solution Behavior
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Ionic and neutral half-sandwich guanidinatoruthenium(II) complexes [(η6-C10H14)RuL(κ2(N,N′){(ArN)2C-N(H)Ar})][OTf] [Ar = 4-MeC6H4, L = 2-methylimidazole (1); Ar = 2-MeC6H4, L = 1,3,5-triaza-7-phosphaadamantane (PTA; 2)], [(ArNH)3C][(η6-C10H14)RuCl3] [Ar = 2-ClC6H4 (3)] and [(η6-C10H14)RuCl(κ2(N,N′){(ArN)2C-N(H)Ar})] [Ar = 2-ClC6H4 (4), 2-FC6H4 (5), 4-ClC6H4 (6), and 4-(NO2)C6H4 (7)] have been isolated and the molecular structures of all but 6 were determined by single-crystal X-ray diffraction. VT 31P{1H} NMR spectroscopy of complex 2 revealed the presence of a mixture of four isomers in a ratio of appproximately 1.4:11.0:1.6:0.1. Theoretical calculations were performed on the syn-syn, syn-anti, anti-syn, and anti-anti conformers of 2, which revealed syn-anti to be the most stable conformer, both in the gas phase and in solution. Furthermore, the energies relating to the interactions between the lone pairs of the nitrogen atoms of the CN3 unit and the antibonding orbital of the central carbon atom in the syn-anti conformer of 2 were investigated by NBO analysis. The 1H NMR spectrum of 3 reveals the presence of two species and their ratio is dependent upon the concentration of 3 in CDCl3 and on the amount of D2O in CD3CN. The two species have been ascribed to the presence of a monomer and a water-bridged dimer. The new complexes 1-7 were screened as pre-catalysts in the transfer hydrogenation of acetophenone and complex 3 was tested as a pre-catalyst in the transfer hydrogenation of a variety of ketones to explore the scope of the reaction.
- Kishan, Ram,Kumar, Robin,Baskaran, Sambath,Sivasankar, Chinnappan,Thirupathi, Natesan
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- Ruthenium complexes bearing an unsymmetrical pincer ligand with a 2-hydroxypyridylmethylene fragment: Active catalysts for transfer hydrogenation of ketones
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Five ruthenium(ii) complexes were synthesized, including (HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)Cl2 (3), [(HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)2Cl][PF6] (4) and [(HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)2OH][PF6] (5) bearing an unsymmetrical pincer NNN ligand with a 2-hydroxypyridylmethylene fragment, and [(CH3O-C5H3N-CH2-C5H3N-C5H4N)2Ru][Cl]2 (6) and [(CH3O-C5H3N-CH2-C5H3N-C5H4N)2Ru][PF6]2 (7) containing 2-methoxypyridylmethylene moieties. 4 reacts with H2O at room temperature to give 5 whose crystal structure reveals the existence of intramolecular hydrogen-bonding between its two -OH groups. 3 exhibits high catalytic activity for transfer hydrogenation of ketones.
- Shi, Jing,Hu, Bowen,Gong, Dawei,Shang, Shu,Hou, Guangfeng,Chen, Dafa
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- Chiral sulfur-containing ligands for iridium(I)-catalyzed asymmetric transfer hydrogenation of aromatic ketones
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New efficient catalyst systems, coupled with IrCl(COD)PPh3 and chiral [SNNS]-type ligands, were employed in the asymmetric transfer hydrogenation of aromatic ketones under mild reaction conditions. The corresponding optically active alcohols we
- Zhang, Xue-Qin,Li, Yan-Yun,Zhang, Hui,Gao, Jing-Xing
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- Ru-η6-benzene-phosphine complex-catalyzed transfer hydrogenation of ketones
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Three Ru-η6-benzene-phosphine complexes bearing tri-(p-methoxyphenyl)phosphine, triphenylphosphine and tri-(p- trifluoromethylphenyl)phosphine were synthesized and characterized by 31P{1H} NMR, 1H NMR, 13C{ 1H} NMR and elemental analyses. Complex 1 was further identified by X-ray crystallography. These complexes exhibit good to excellent activities for the transfer hydrogenation of ketones in refluxing 2-propanol, and the highest turnover frequency (TOF) is up to 5940 h-1. The effect of electronic factors of these complexes on the transfer hydrogenation of ketones reveals that the catalytic activity is promoted by electron-donating phosphine and the catalyst stability is improved by electron-withdrawing phosphine.
- Wang, Lei,Yang, Qin,Fu, Hai-Yan,Chen, Hua,Yuan, Mao-Lin,Li, Rui-Xiang
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- New chiral cationic rhodium-aminophosphine complexes for asymmetric transfer hydrogenation of aromatic ketones
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The new chiral ligands (S,S)-N,N′-bis[o-(diphenylphosphino)benzylidene]1,2-diiminocyclohexane, [(S,S)-1] and (S,S)-N,N′-bis[o-diphenylphosphino]benzyl-1,2-diaminocyclohexane, [(S,S)-2] have been prepared. The interaction of [(S,S)-1] and [(S,S)-2] with [Rh(COD)Cl]2 afforded the corresponding cationic rhodium complexes [(S,S)-3][X] and [(S,S)-4][X] (X=PF6-, BF4- or ClO4-), respectively. [(S,S)-1], [(S,S)-2], [(S,S)-3][X] and [(S,S)-4][X] have been fully characterized by elemental analyses and spectroscopic methods. These chiral cationic rhodium complexes serve as catalytst precursors for the asymmetric transfer hydrogenation of acetophenone derivatives in 2-propanol and [(S,S)-4][PF6] acts as an excellent catalyst in the reduction of m-chloroacetophenone, giving the corresponding optical alcohols in 99% yield and up to 94% ee.
- Gao, Jing-Xing,Yi, Xiao-Dong,Xu, Pian-Pian,Tang, Chun-Liang,Wan, Hui-Lin,Ikariya, Takao
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- Exceptionally Active Assembled Dinuclear Ruthenium(II)-NNN Complex Catalysts for Transfer Hydrogenation of Ketones
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Dinuclear ruthenium(II)-NNN complexes were efficiently assembled by means of coordinatively unsaturated 16-electron mononuclear ruthenium(II)-pyrazolyl-imidazolyl-pyridine complex and 4,4′-linked bipyridine ligands. The diruthenium(II)-NNN complex assembled through 4,4′-(CH2)3-bipyridine exhibited exceptionally high catalytic activity for the transfer hydrogenation (TH) of ketones in refluxing 2-propanol and reached TOF values up to 1.4 × 107 h-1, demonstrating a remarkable cooperative effect from the ruthenium(II)-NNN functionalities.
- Liu, Tingting,Chai, Huining,Wang, Liandi,Yu, Zhengkun
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- Lipase-Catalyzed Transesterification of Aryl-Substituted Alkanols in an Organic Solvent
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Lipase-catalyzed transesterifications of aryl-substituted alcohols with vinyl acetate in organic solvents have been investigated. Vmax of (R)-1-phenylethanol is much larger than its (S)-counterpart, although their Kms are similar each other. It is proposed that a lipase from Pseudomonas cepacia can form a complex easily with each enantiomer, although the complex with the (S)-enantiomer is abortive. Enantioselectivity for the ortho-substituted 1-phenylethanol is smaller than those for the others. A three-dimensional model for the active domain of the lipase has been proposed to explain the enantioselectivity and substrate selectivity of the lipase.
- Nakamura, Kaoru,Kawasaki, Masashi,Ohno, Atsuyoshi
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- Cooperative N-H and CH2 Skeleton Effects on the Catalytic Activities of Bimetallic Ru(II)-NNN Complexes: Experimental and Theoretical Study
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Bimetallic ruthenium(II) complexes bearing a bis(pyrazolylimidazolylpyridine) ligand bridged by a rotatable single C-C bond or methylene linker were synthesized, structurally characterized, and exhibited diverse catalytic activities for the transfer hydrogenation (TH) reactions of ketones in refluxing isopropyl alcohol. Both the unprotected NH functionality and bridging methylene moiety demonstrated an acceleration effect on such TH reactions. Combination of the NH and CH2 skeleton functionalities into the bimetallic Ru(II)-NNN complexes remarkably enhanced the catalytic activities of the complex catalysts. Density functional theory calculations have suggested that the difference in the catalytic activities of these Ru(II)-NNN complexes is attributed to the inherent nucleophilic character of the coordinative nitrogen atoms in the bis(NNN) ligand, and the metal-metal interaction resulted from the number of net natural bond orbital charges on these nitrogen atoms.
- Chai, Huining,Liu, Tingting,Zheng, Daoyuan,Yu, Zhengkun
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- A Cobalt(II) Complex Bearing the Amine(imine)diphosphine PN(H)NP Ligand for Asymmetric Transfer Hydrogenation of Ketones
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Novel chiral cobalt complex a containing amine(imine)diphosphine PN(H)NP ligand and complex b containing bis(amine)diphosphine PN(H)N(H)P ligand were synthesized. The structures of two complexes were characterized by X-ray crystallography and high resolution mass spectrometry. The catalytic performances of cobalt complexes a and b for asymmetric transfer hydrogenation (ATH) of ketones under mild conditions were evaluated using 2-propanolisopropanol as solvent and hydrogen source after being activated by 8 equivalents of base. Complex a showed a good reactivity for reduction of ketones, with a turnover number (TON) of up to 555, and a maximum enantiomeric excess (ee) value of up to 91 %. Complex b exhibited inertness for hydrogenation of ketones. Electronic structure studies on a and b were conducted to account for the function of ligands on the catalytic performances.
- Huo, Shangfei,Chen, Hong,Zuo, Weiwei
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- What to sacrifice? Fusions of cofactor regenerating enzymes with Baeyer-Villiger monooxygenases and alcohol dehydrogenases for self-sufficient redox biocatalysis
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A collection of fusion biocatalysts has been generated that can be used for self-sufficient oxygenations or ketone reductions. These biocatalysts were created by fusing a Baeyer-Villiger monooxygenase (cyclohexanone monooxygenase from Thermocrispum municipale: TmCHMO) or an alcohol dehydrogenase (alcohol dehydrogenase from Lactobacillus brevis: LbADH) with three different cofactor regeneration enzymes (formate dehydrogenase from Burkholderia stabilis: BsFDH; glucose dehydrogenase from Sulfolobus tokodaii: StGDH, and phosphite dehydrogenase from Pseudomonas stutzeri: PsPTDH). Their tolerance against various organic solvents, including a deep eutectic solvent, and their activity and selectivity with a variety of substrates have been studied. Excellent conversions and enantioselectivities were obtained, demonstrating that these engineered fusion enzymes can be used as biocatalysts for the synthesis of (chiral) valuable compounds.
- Mourelle-Insua, ángela,Aalbers, Friso S.,Lavandera, Iván,Gotor-Fernández, Vicente,Fraaije, Marco W.
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- Asymmetric hydrosilylation of aromatic ketones catalyzed by an economical and effective copper-diphosphine catalytic system in air
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In the presence of the inexpensive and non-toxic polymethylhydrosiloxane, the combination of copper(II) acetate and a chiral diphosphine displayed high catalytic efficiency in the asymmetric hydrosilylation of a series of aromatic ketones in air atmospher
- Liang, Minting,Xia, Xiaofeng,Liu, Xiang,Li, Hexing
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- Highly enantioselective reduction of ketones in air catalyzed by Rh-based macrocycles
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The asymmetric transfer hydrogenation (ATH) of ketones catalyzed by Rh-based macrocycles proceeded smoothly in the presence of air with high catalytic activity and enantioselectivity. Even though the S/C ratio (substrate to catalyst molar ratio) was incre
- Zhang, Wen-Jing,Ruan, Sun-Hong,Shen, Wei-Yi,Wang, Zhe,An, Dong-Li,Li, Yan-Yun,Gao, Jing-Xing
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- Reduction of acetophenone using supercritical 2-propanol: The substituent effect and the deuterium kinetic isotope effect
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The reductions of several substituted acetophenones using supercritical 2-propanol were carried out to estimate the Hammett's reaction constant (ρ=0.33). Also, the reduction of acetophenone using supercritical deuteriated 2-propanol was carried out to determine the rate-determining step. The kinetic isotope effects were observed in the reduction using 2-deuterio-2-propanol (kH/kD=1.6) and O-deuterio-2-propanol (kH/kD=2.0). These findings suggest that the reaction proceeds via a cyclic transition state between acetophenone and 2-propanol similar to that of the Meerwein-Ponndorf-Verley reduction.
- Kamitanaka, Takashi,Matsuda, Tomoko,Harada, Tadao
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- Enhancing cofactor regeneration of cyanobacteria for the light-powered synthesis of chiral alcohols
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Cyanobacteria Synechocystis sp. PCC 6803 was exploited as green cell factory for light-powered asymmetric synthesis of aromatic chiral alcohols. The effect of temperature, light, substrate and cell concentration on substrate conversions were investigated. Under the optimal condition, a series of chiral alcohols were synthesized with conversions up to 95% and enantiomer excess (ee) > 99%. We found that the addition of Na2S2O3 and Angeli's Salt increased the NADPH content by 20% and 25%, respectively. As a result, the time to reach 95% substrate conversion was shortened by 12 h, which demonstrated that the NADPH regeneration and hence the reaction rates can be regulated in cyanobacteria. This blue-green algae based biocatalysis showed its potential for chiral compounds production in future.
- Fan, Jianhua,Zhang, Yinghui,Wu, Ping,Zhang, Xiaoyan,Bai, Yunpeng
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- Cobalt-catalyzed asymmetric hydrogenation of ketones: A remarkable additive effect on enantioselectivity
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A chiral cobalt pincer complex, when combined with an achiral electron-rich mono-phosphine ligand, catalyzes efficient asymmetric hydrogenation of a wide range of aryl ketones, affording chiral alcohols with high yields and moderate to excellent enantioselectivities (29 examples, up to 93% ee). Notably, the achiral mono-phosphine ligand shows a remarkable effect on the enantioselectivity of the reaction.
- Du, Tian,Wang, Biwen,Wang, Chao,Xiao, Jianliang,Tang, Weijun
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supporting information
p. 1241 - 1244
(2020/10/02)
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- Manganese catalyzed asymmetric transfer hydrogenation of ketones
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The asymmetric transfer hydrogenation (ATH) of a wide range of ketones catalyzed by manganese complex as well as chiral PxNy-type ligand under mild conditions was investigated. Using 2-propanol as hydrogen source, various ketones could be enantioselectively hydrogenated by combining cheap, readily available [MnBr(CO)5] with chiral, 22-membered macrocyclic ligand (R,R,R',R')-CyP2N4 (L5) with 2 mol% of catalyst loading, affording highly valuable chiral alcohols with up to 95% ee.
- Zhang, Guang-Ya,Ruan, Sun-Hong,Li, Yan-Yun,Gao, Jing-Xing
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supporting information
p. 1415 - 1418
(2020/11/20)
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- Effectiveness and Mechanism of the Ene(amido) Group in Activating Iron for the Catalytic Asymmetric Transfer Hydrogenation of Ketones
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I-interacting ligands of the diphosphino amido-ene(amido) type are effective in activating iron to resemble the properties of precious metals in the catalytic asymmetric transfer hydrogenation of ketones. To further verify the effectiveness of the ene(amido) group, we synthesized four amine(imine) diphosphine iron precatalyst complexes with substituents at α and β positions relative to imino groups (1-3) or with enlarged chelate ring sizes (5,5,6-membered rings) (4). In comparison with the parent trans-(R,R)-[Fe(CO)(Cl)(PPh2CH2CHaNCHPhCHPhNHCH2CH2PPh2)]BF4 (I), the introduction of a methyl group in 1 and 2 reduced the catalytic activity but led to undiminished enantioselectivity as reaction proceeded. In comparison to the iron complexes 1-3 with a 5,5,5-coordination geometry, the complex 4 derived from the new (R,R)-P-NH-NH2 tridentate ligand showed high reactivity comparable to that of I but was unfortunately not enantioselective. The catalytic reactivity of 1, 2, and 4 illustrates the effectiveness of the ene(amido) group. An electronic structure study on the important catalytic intermediate amido-ene(amido) complex 1b proved that iron was activated by an additional I-back-donation-interaction ligand to participate in the traditional metal-ligand bifunctional pathway in the asymmetric transfer hydrogenation reactions.
- Xue, Qingquan,Wu, Rongliang,Wang, Di,Zhu, Meifang,Zuo, Weiwei
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supporting information
p. 134 - 147
(2021/02/05)
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- Highly Active Cooperative Lewis Acid—Ammonium Salt Catalyst for the Enantioselective Hydroboration of Ketones
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Enantiopure secondary alcohols are fundamental high-value synthetic building blocks. One of the most attractive ways to get access to this compound class is the catalytic hydroboration. We describe a new concept for this reaction type that allowed for exceptional catalytic turnover numbers (up to 15 400), which were increased by around 1.5–3 orders of magnitude compared to the most active catalysts previously reported. In our concept an aprotic ammonium halide moiety cooperates with an oxophilic Lewis acid within the same catalyst molecule. Control experiments reveal that both catalytic centers are essential for the observed activity. Kinetic, spectroscopic and computational studies show that the hydride transfer is rate limiting and proceeds via a concerted mechanism, in which hydride at Boron is continuously displaced by iodide, reminiscent to an SN2 reaction. The catalyst, which is accessible in high yields in few steps, was found to be stable during catalysis, readily recyclable and could be reused 10 times still efficiently working.
- Titze, Marvin,Heitk?mper, Juliane,Junge, Thorsten,K?stner, Johannes,Peters, René
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supporting information
p. 5544 - 5553
(2021/02/05)
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- First application of chiral phosphotriesters in asymmetric metal catalysis: Enantioselective zn-catalyzed hydrosilylation of ketones in the presence of binol-derived phosphates
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Chiral phosphotriesters are an unexplored class of ligands in metal catalysis. We wish to disclose herein the foremost application of novel chiral BINOL-derived mono- A nd bisphosphates in asymmetric zinc-catalyzed hydrosilylation of ketones. Corresponding alcohols were obtained in up to 92% yield and 34% ee.
- Ndimba, Alphonsine Ngo,Roisnel, Thierry,Argouarch, Gilles,Lalli, Claudia
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- Asymmetric reduction of prochiral aromatic and hetero aromatic ketones using whole-cell of Lactobacillus senmaizukei biocatalyst
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Asymmetric bioreduction of aromatic and heteroaromatic ketones is an important process in the production of precursors of biologically active molecules. In this study, the bioreduction of aromatic and hetero aromatic prochiral ketones into optically active alcohols was investigated using Lactobacillus senmaizukei as a whole-cell catalyst, since whole-cells are less expensive than pure enzymes. The study indicates enantioselective bioreduction of various substituted aromatic ketones (1–16) to the corresponding (R)-and (S)-chiral secondary alcohols (1a–16a) in low to excellent enantioselectivity (6–94%) with good yields (58–95%). In addition, heteroaromatic prochiral ketones 1-(pyridin-2-yl)ethanone (17) and 1-(furan-2-yl)ethanone (18) were reduced to (R)-17a and (R)-18a in enantiopure form with excellent conversion (>99%) and yields. These findings show that L. senmaizukei is a very important biocatalyst for asymmetric reduction of both 6-membered and 5-member heteroaromatic methyl ketones. This method promising a green synthesis for the synthesis of biologically important secondary chiral alcohols in an environmentally friendly and inexpensive process.
- ?olak, Nida Sezin,Kalay, Erbay,?ahin, Engin
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p. 2305 - 2315
(2021/05/31)
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- Enantioselective Hydroboration of Ketones Catalyzed by Rare-Earth-Metal Complexes Supported with Phenoxy-Functionalized TsDPEN Ligands
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Six novel chiral rare-earth-metal complexes bearing the phenoxy-functionalized TsDPEN ligand H3L1 (H3L1 = N-((1R,2R)-2-((3,5-di-Tert-butyl-2-hydroxybenzyl)amino)-1,2-diphenylethyl)-4-methylbenzenesulfonamide) were synthesized successfully and well characterized. The solid-state structures of four tetranuclear rare-earth-metal complexes [RE2L13]2 (RE = Nd (1), Sm (2), Eu (3), Gd (4)) and the dual-core yttrium complex Y2L13 (5) were determined by X-ray diffraction, respectively. The structure of lanthanum complex 6 was speculated by the 1H DOSY spectroscopy in THF-d8 together with DFT calculations. Complexes 1-5 were employed to catalyze the enantioselective hydroboration of ketones and α,β-unsaturated ketones using pinacolborane (HBpin) as a reductant, and complex 1 gave better outcomes in comparison to the others. The corresponding secondary alcohols were obtained in excellent yields and moderate ee values. The same results were also achieved using the combined catalyst system of the neodymium amide Nd[N(SiMe3)2]3 with the phenoxy-functionalized TsDPEN ligand H3L1 in a 1:1.5 molar ratio.
- Yu, Qishun,Lu, Chengrong,Zhao, Bei
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p. 2529 - 2537
(2021/07/28)
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- Biocatalytic preparation of a key intermediate of antifungal drugs using an alcohol dehydrogenase with high organic tolerance
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In this study, an alcohol dehydrogenase derived from Lactobacillus kefir (LkADH) was engineered and a simple and practical bioreduction system was developed for the preparation of (R)-2-chloro-1-(2, 4-dichlorophenyl) ethanol ((R)-CDPO), a key intermediate for the synthesis of antifungal drugs. Through active pocket iterative saturation mutagenesis, mutant LkADH-D18 (Y190C/V196L/M206H/D150H) was obtained with high stereoselectivity (99% ee, R vs 87% ee, S) and increased activity (0.44 μmol·min?1·mg?1). LkADH-D18 demonstrated NAD(P)H regeneration capability using a high concentration of isopropanol (IPA) as a co-substrate. Using 40% IPA (v/v), 400 mM of (R)-CDPO (90.1 g·L-1) was obtained via complete substrate conversion using 40 mg·mL?1 LkADH-D18 wet cells. The biocatalytic process catalyzed at constant pH with the cheap co-solvent IPA contributed to improved isolated yield of (R)-CDPO (97%), lower reaction cost, and simpler downstream purification, indicating the potential utility of LkADH-D18 in future industrial applications.
- Yan, Jinrong,Wang, Xiaojing,Li, Fangling,Yang, Lei,Shi, Guixiang,Sun, Weihang,Shao, Lei,Huang, Junhai,Wu, Kai
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supporting information
(2021/10/20)
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- Mn(i) phosphine-amino-phosphinites: a highly modular class of pincer complexes for enantioselective transfer hydrogenation of aryl-alkyl ketones
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A series of Mn(i) catalysts with readily accessible and more π-accepting phosphine-amino-phosphinite (P′(O)N(H)P) pincer ligands have been explored for the asymmetric transfer hydrogenation of aryl-alkyl ketones which led to good to high enantioselectivities (up to 98%) compared to other reported Mn-based catalysts for such reactions. The easy tunability of the chiral backbone and the phosphine moieties makes P′(O)N(H)P an alternative ligand framework to the well-known PNP-type pincers.
- Jayaprakash, Harikrishnan
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supporting information
p. 14115 - 14119
(2021/10/25)
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- Mechanochemical, Water-Assisted Asymmetric Transfer Hydrogenation of Ketones Using Ruthenium Catalyst
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Asymmetric catalytic reactions are among the most convenient and environmentally benign methods to obtain optically pure compounds. The aim of this study was to develop a green system for the asymmetric transfer hydrogenation of ketones, applying chiral Ru catalyst in aqueous media and mechanochemical energy transmission. Using a ball mill we have optimized the milling parameters in the transfer hydrogenation of acetophenone followed by reduction of various substituted derivatives. The scope of the method was extended to carbo- and heterocyclic ketones. The scale-up of the developed system was successful, the optically enriched alcohols could be obtained in high yields. The developed mechanochemical system provides TOFs up to 168 h?1. Our present study is the first in which mechanochemically activated enantioselective transfer hydrogenations were carried out, thus, may be a useful guide for the practical synthesis of optically pure chiral secondary alcohols.
- Kolcsár, Vanessza Judit,Sz?ll?si, Gy?rgy
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- Synthesis and catalytic activity of N-heterocyclic silylene (NHSi) iron (II) hydride for hydrosilylation of aldehydes and ketones
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A novel silylene supported iron hydride [Si, C]FeH (PMe3)3 (1) was synthesized by C (sp3)-H bond activation with zero-valent iron complex Fe (PMe3)4. Complex 1 was fully characterized by spectroscopic methods and single crystal X-ray diffraction analysis. To the best of our knowledge, 1 is the first example of silylene-based hydrido chelate iron complex produced through activation of the C (sp3)?H bond. It was found that complex 1 exhibited excellent catalytic activity for hydrosilylation of aldehydes and ketones. The catalytic system showed good tolerance and catalytic activity for the substrates with different functional groups on the benzene ring. It is worth mentioning that, the experimental results showed that both ketones and aldehydes could be reduced in good to excellent yields under the same catalytic conditions. Based on the experiments and literature reports, a possible catalytic mechanism was proposed.
- Du, Xinyu,Qi, Xinghao,Li, Kai,Li, Xiaoyan,Sun, Hongjian,Fuhr, Olaf,Fenske, Dieter
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- Pincerlike molybdenum complex and preparation method thereof, catalytic composition and application thereof, and alcohol preparation method
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The invention discloses a clamp-type molybdenum complex, a preparation method, a corresponding catalyst composition and application. The method comprises the steps: obtaining 9 molybdenum complexes with different structures through coordination reaction of 2-(substituent ethyl)-(5, 6, 7, 8-tetrahydroquinolyl) amine and a corresponding carbonyl molybdenum metal precursor; and catalyzing a ketone compound transfer hydrogenation reaction through a molybdenum complex to generate 40 alcohol compounds. The preparation method of the molybdenum complex is simple, high in yield and good in stability. For a transfer hydrogenation reaction of ketone, the molybdenum-based catalytic system has high catalytic activity and small molybdenum loading capacity, is used for production of aromatic and aliphatic alcohols, and has the advantages of simple method, small environmental pollution and high yield.
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Paragraph 0125-0130
(2021/08/11)
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- Hydrogen-Catalyzed Acid Transformation for the Hydration of Alkenes and Epoxy Alkanes over Co-N Frustrated Lewis Pair Surfaces
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Hydrogen (H2) is widely used as a reductant for many hydrogenation reactions; however, it has not been recognized as a catalyst for the acid transformation of active sites on solid surface. Here, we report the H2-promoted hydration of alkenes (such as styrenes and cyclic alkenes) and epoxy alkanes over single-atom Co-dispersed nitrogen-doped carbon (Co-NC) via a transformation mechanism of acid-base sites. Specifically, the specific catalytic activity and selectivity of Co-NC are superior to those of classical solid acids (acidic zeolites and resins) per micromole of acid, whereas the hydration catalysis does not take place under a nitrogen atmosphere. Detailed investigations indicate that H2 can be heterolyzed on the Co-N bond to form Hδ-Co-N-Hδ+ and then be converted into OHδ-Co-N-Hδ+ accompanied by H2 generation via a H2O-mediated path, which significantly reduces the activation energy for hydration reactions. This work not only provides a novel catalytic method for hydration reactions but also removes the conceptual barriers between hydrogenation and acid catalysis.
- Deng, Qiang,Deng, Shuguang,Gao, Ruijie,Li, Xiang,Tsang, Shik Chi Edman,Wang, Jun,Zeng, Zheling,Zou, Ji-Jun
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p. 21294 - 21301
(2021/12/17)
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- Manganese-catalyzed homogeneous hydrogenation of ketones and conjugate reduction of α,β-unsaturated carboxylic acid derivatives: A chemoselective, robust, and phosphine-free in situ-protocol
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We communicate a user-friendly and glove-box-free catalytic protocol for the manganese-catalyzed hydrogenation of ketones and conjugated C[dbnd]C[sbnd]bonds of esters and nitriles. The respective catalyst is readily assembled in situ from the privileged [Mn(CO)5Br] precursor and cheap 2-picolylamine. The catalytic transformations were performed in the presence of t-BuOK whereby the corresponding hydrogenation products were obtained in good to excellent yields. The described system offers a brisk and atom-efficient access to both secondary alcohols and saturated esters avoiding the use of oxygen-sensitive and expensive phosphine-based ligands.
- Topf, Christoph,Vielhaber, Thomas
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- Ambient-pressure highly active hydrogenation of ketones and aldehydes catalyzed by a metal-ligand bifunctional iridium catalyst under base-free conditions in water
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A green, efficient, and high active catalytic system for the hydrogenation of ketones and aldehydes to produce corresponding alcohols under atmospheric-pressure H2 gas and ambient temperature conditions was developed by a water-soluble metal–ligand bifunctional catalyst [Cp*Ir(2,2′-bpyO)(OH)][Na] in water without addition of a base. The catalyst exhibited high activity for the hydrogenation of ketones and aldehydes. Furthermore, it was worth noting that many readily reducible or labile functional groups in the same molecule, such as cyan, nitro, and ester groups, remained unchanged. Interestingly, the unsaturated aldehydes can be also selectively hydrogenated to give corresponding unsaturated alcohols with remaining C=C bond in good yields. In addition, this reaction could be extended to gram levels and has a large potential of wide application in future industrial.
- Wang, Rongzhou,Yue, Yuancheng,Qi, Jipeng,Liu, Shiyuan,Song, Ao,Zhuo, Shuping,Xing, Ling-Bao
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- Selective C-alkylation Between Alcohols Catalyzed by N-Heterocyclic Carbene Molybdenum
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The first implementation of a molybdenum complex with an easily accessible bis-N-heterocyclic carbene ligand to catalyze β-alkylation of secondary alcohols via borrowing-hydrogen (BH) strategy using alcohols as alkylating agents is reported. Remarkably high activity, excellent selectivity, and broad substrate scope compatibility with advantages of catalyst usage low to 0.5 mol%, a catalytic amount of NaOH as the base, and H2O as the by-product are demonstrated in this green and step-economical protocol. Mechanistic studies indicate a plausible outer-sphere mechanism in which the alcohol dehydrogenation is the rate-determining step.
- Liu, Jiahao,Li, Weikang,Li, Yinwu,Liu, Yan,Ke, Zhuofeng
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supporting information
p. 3124 - 3128
(2021/09/20)
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- Ruthenium complex based on [N,N,O] tridentate -2-ferrocenyl-2-thiazoline ligand for catalytic transfer hydrogenation
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A method for the synthesis of a new phosphine-free [N,N,O]-tridentate Schiff base ligand L1 using the 2-Ferrocenyl-2-thiazoline as scaffold was developed. The 1,2-disubstituted ferrocene-based ligand was assembled using as key strategy the directed ortho-metalation (DoM) in 2-ferrocenyl-2-thiazoline. L1 was successfully obtained in 83% of overall yield after two-step synthesis. The coordination ability of L1 towards Ru(II) was evidenced and the resulting complex was characterized by IR, UV-vis and EPR. Its catalytic performance was tested in transfer hydrogenation of a variety of substrates giving moderate to excellent conversions.
- Badillo-Gómez,Sánchez-Rodríguez,Toscano,Gouygou,Ortega-Alfaro,López-Cortés
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- Postsynthetic Modification of Half-Sandwich Ruthenium Complexes by Mechanochemical Synthesis
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A mild and environmentally friendly method to synthesize half-sandwich ruthenium complexes through the Wittig reaction between an aldehyde-tagged half-sandwich ruthenium complex and phosphorus ylide mechanochemically is reported herein. The mechanochemical synthesis of valuable half-sandwich ruthenium complexes resulted in a fast reaction, good yield with simple workup, and the avoidance of harsh reaction conditions and organic solvents. The synthesized half-sandwich ruthenium complexes exhibited high catalytic activity for transfer hydrogenation of ketones using 2-propanol as the hydrogen source and solvent. Density functional theory was carried out to propose a mechanism for the transfer hydrogenation process. The modeling suggests the importance of the labile p-cymene ligand in modulating the reactivity of the catalyst.
- Jia, Wei-Guo,Zhi, Xue-Ting,Li, Xiao-Dong,Zhou, Jun-Peng,Zhong, Rui,Yu, Haibo,Lee, Richmond
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p. 4313 - 4321
(2021/05/04)
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- Tridentate nitrogen phosphine ligand containing arylamine NH as well as preparation method and application thereof
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The invention discloses a tridentate nitrogen phosphine ligand containing arylamine NH as well as a preparation method and application thereof, and belongs to the technical field of organic synthesis. The tridentate nitrogen phosphine ligand disclosed by the invention is the first case of tridentate nitrogen phosphine ligand containing not only a quinoline amine structure but also chiral ferrocene at present, a noble metal complex of the type of ligand shows good selectivity and extremely high catalytic activity in an asymmetric hydrogenation reaction, meanwhile, a cheap metal complex of the ligand can also show good selectivity and catalytic activity in the asymmetric hydrogenation reaction, and is very easy to modify in the aspects of electronic effect and space structure, so that the ligand has huge potential application value. A catalyst formed by the ligand and a transition metal complex can be used for catalyzing various reactions, can be used for synthesizing various drugs, and has important industrial application value.
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Paragraph 0095-0102; 0105-0109
(2021/06/26)
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- Efficient asymmetric synthesis of chiral alcohols using high 2-propanol tolerance alcohol dehydrogenase: Sm ADH2 via an environmentally friendly TBCR system
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Alcohol dehydrogenases (ADHs) together with the economical substrate-coupled cofactor regeneration system play a pivotal role in the asymmetric synthesis of chiral alcohols; however, severe challenges concerning the poor tolerance of enzymes to 2-propanol and the adverse effects of the by-product, acetone, limit its applications, causing this strategy to lapse. Herein, a novel ADH gene smadh2 was identified from Stenotrophomonas maltophilia by traditional genome mining technology. The gene was cloned into Escherichia coli cells and then expressed to yield SmADH2. SmADH2 has a broad substrate spectrum and exhibits excellent tolerance and superb activity to 2-propanol even at 10.5 M (80%, v/v) concentration. Moreover, a new thermostatic bubble column reactor (TBCR) system is successfully designed to alleviate the inhibition of the by-product acetone by gas flow and continuously supplement 2-propanol. The organic waste can be simultaneously recovered for the purpose of green synthesis. In the sustainable system, structurally diverse chiral alcohols are synthesised at a high substrate loading (>150 g L-1) without adding external coenzymes. Among these, about 780 g L-1 (6 M) ethyl acetoacetate is completely converted into ethyl (R)-3-hydroxybutyrate in only 2.5 h with 99.9% ee and 7488 g L-1 d-1 space-time yield. Molecular dynamics simulation results shed light on the high catalytic activity toward the substrate. Therefore, the high 2-propanol tolerance SmADH2 with the TBCR system proves to be a potent biocatalytic strategy for the synthesis of chiral alcohols on an industrial scale.
- Yang, Zeyu,Fu, Hengwei,Ye, Wenjie,Xie, Youyu,Liu, Qinghai,Wang, Hualei,Wei, Dongzhi
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- Asymmetric Hydrogenation of Ketones and Enones with Chiral Lewis Base Derived Frustrated Lewis Pairs
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The concept of frustrated Lewis pairs (FLPs) has been widely applied in various research areas, and metal-free hydrogenation undoubtedly belongs to the most significant and successful ones. In the past decade, great efforts have been devoted to the synthesis of chiral boron Lewis acids. In a sharp contrast, chiral Lewis base derived FLPs have rarely been disclosed for the asymmetric hydrogenation. In this work, a novel type of chiral FLP was developed by simple combination of chiral oxazoline Lewis bases with achiral boron Lewis acids, thus providing a promising new direction for the development of chiral FLPs in the future. These chiral FLPs proved to be highly effective for the asymmetric hydrogenation of ketones, enones, and chromones, giving the corresponding products in high yields with up to 95 % ee. Mechanistic studies suggest that the hydrogen transfer to simple ketones likely proceeds in a concerted manner.
- Du, Haifeng,Feng, Xiangqing,Gao, Bochao,Meng, Wei
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supporting information
p. 4498 - 4504
(2020/02/05)
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- Control of enantioselectivity in the enzymatic reduction of halogenated acetophenone analogs by substituent positions and sizes
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We utilized acetophenone reductase from Geotrichum candidum NBRC 4597 (GcAPRD), wild type and Trp288Ala mutant, to reduce halogenated acetophenone analogs to their corresponding (S)- and (R)-alcohols beneficial as pharmaceutical intermediates. Reduction by wild type resulted in excellent (S)-enantioselectivity for all of the substrates tested. Meanwhile, reduction by Trp288Ala resulted in high (R)-enantioselectivity for the reduction of 4′ substituted acetophenone and 2′-trifluoromethylacetophenone. In addition to that, we were able to control the enantioselectivity of Trp288Ala by the positions and sizes of the halogen substituents.
- Koesoema, Afifa Ayu,Standley, Daron M.,Ohshima, Shusuke,Tamura, Mayumi,Matsuda, Tomoko
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supporting information
(2020/03/23)
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- Engineering an alcohol dehydrogenase with enhanced activity and stereoselectivity toward diaryl ketones: Reduction of steric hindrance and change of the stereocontrol element
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Steric hindrance in the binding pocket of an alcohol dehydrogenase (ADH) has a great impact on its activity and stereoselectivity simultaneously. Due to the subtle structural difference between two bulky phenyl substituents, the asymmetric synthesis of diaryl alcohols by bioreduction of diaryl ketones is often hindered by the low activity and stereoselectivity of ADHs. To engineer an ADH with practical properties and to investigate the molecular mechanism behind the asymmetric biocatalysis of diaryl ketones, we engineered an ADH from Lactobacillus kefiri (LkADH) to asymmetrically catalyse the reduction of 4-chlorodiphenylketones (CPPK), which are not catalysed by the wild type (WT) enzyme. Mutants seq1-seq5 with gradually increased activity and stereoselectivity were obtained through iterative "shrinking mutagenesis." The final mutant seq5 (Y190P/I144V/L199V/E145C/M206F) demonstrated the highest activity and excellent stereoselectivity of >99% ee. Molecular simulation analyses revealed that mutations may enhance the activity by eliminating steric hindrance, inducing a more open binding loop and constructing more noncovalent interactions. The pro-R pose of CPPK with a halogen bond formed a pre-reaction conformation more easily than the pro-S pose, resulting in the high ee of (R)-CPPO in seq5. Moreover, different halogen bonds formed due to the different positions of chlorine substituents, resulting in opposite substrate binding orientation and stereoselectivity. Therefore, the stereoselectivity of seq5 was inverted toward ortho- rather than para-chlorine substituted ketones. These results indicate that the stereocontrol element of LkADH was changed to recognise diaryl ketones after steric hindrance was eliminated. This study provides novel insights into the role of steric hindrance and noncovalent bonds in the determination of the activity and stereoselectivity of enzymes, and presents an approach producing key intermediates of chiral drugs with practical potential.
- Chen, Rong,Huang, Jiankun,Meng, Xiangguo,Shao, Lei,Wu, Kai,Yang, Zhijun
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p. 1650 - 1660
(2020/04/09)
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- Chiral amino-pyridine-phosphine tridentate ligand, manganese complex, and preparation method and application thereof
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The invention discloses a chiral amino-pyridine-phosphine tridentate ligand, a manganese complex, and a preparation method and application thereof. The chiral amino-pyridine-phosphine tridentate ligand is shown as a formula II, and the manganese complex of the chiral amino-pyridine-phosphine tridentate ligand can be used for efficiently catalyzing and hydrogenating ketone compounds to prepare chiral alcohol compounds in a high enantioselectivity mode. The chiral amino-pyridine-phosphine tridentate ligand and the manganese complex are simple in synthesis process, good in stability, high in catalytic activity and mild in reaction conditions.
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Paragraph 0597-0599; 0601
(2020/07/13)
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- Enantioselective Hydroboration of Ketones Catalyzed by Rare-Earth Metal Complexes Containing Trost Ligands
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Four chiral dinuclear rare-earth metal complexes [REL1]2 (RE = Y(1), Eu(2), Nd(3), La (4)) stabilized by Trost proligand H3L1 (H3L1 = (S,S)-2,6-bis[2-(hydroxydiphenylmethyl)pyrrolidin-1-ylmethyl]-4-methylphenol) were first prepared, and all were characterized by X-ray diffraction. Complex 4 was employed as the catalyst for enantioselective hydroboration reaction of substituted ketones, and the corresponding secondary alcohols with excellent yields and high ee values were obtained using reductant HBpin. The same result was also achieved using the combination of lanthanium amides La[N(SiMe3)2]3 with Trost proligand H3L1 in a 1:1 molar ratio. The experimental findings and DFT calculation revealed the possible mechanism of the enantioselective hydroboration reaction and defined the origin of the enantioselectivity in the current system.
- Lu, Chengrong,Sun, Yuli,Xue, Mingqiang,Zhao, Bei
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p. 10504 - 10513
(2020/09/23)
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- C1-Symmetric PNP Ligands for Manganese-Catalyzed Enantioselective Hydrogenation of Ketones: Reaction Scope and Enantioinduction Model
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A family of ferrocene-based chiral PNP ligands is reported. These tridentate ligands were successfully applied in Mn-catalyzed asymmetric hydrogenation of ketones, giving high enantioselectivities (92%~99% ee for aryl alkyl ketones) as well as high efficiencies (TON up to 2000). In addition, dialkyl ketones could also be hydrogenated smoothly. Manganese intermediates that might be involved in the catalytic cycle were analyzed. DFT calculation was carried out to help understand the chiral induction model. The Mn/PNP catalyst could discriminate two groups with different steric properties by deformation of the phosphine moiety in the flexible 5-membered ring.
- Zeng, Liyao,Yang, Huaxin,Zhao, Menglong,Wen, Jialin,Tucker, James H. R.,Zhang, Xumu
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p. 13794 - 13799
(2020/11/30)
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- RETRACTED ARTICLE: The Manganese(I)-Catalyzed Asymmetric Transfer Hydrogenation of Ketones: Disclosing the Macrocylic Privilege
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The bis(carbonyl) manganese(I) complex [Mn(CO)2(1)]Br (2) with a chiral (NH)2P2 macrocyclic ligand (1) catalyzes the asymmetric transfer hydrogenation of polar double bonds with 2-propanol as the hydrogen source. Ketones (43 substrates) are reduced to alcohols in high yields (up to >99 %) and with excellent enantioselectivities (90–99 % ee). A stereochemical model based on attractive CH–π interactions is proposed.
- Passera, Alessandro,Mezzetti, Antonio
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supporting information
p. 187 - 191
(2019/12/11)
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- Stereoselective synthesis of the key intermediate of ticagrelor and its diverse analogs using a new alcohol dehydrogenase from Rhodococcus kyotonensis
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Bioreduction catalyzed by alcohol dehydrogenase/reductase is one of the most valuable biotransformation processes widely used in industry. The (S)-2-Chloro-1-(3, 4-difluorophenyl) ethanol is a key chiral synthon for synthesizing the antithrombotic agent ticagrelor. Herein, a new alcohol dehydrogenase (named Rhky-ADH) identified from Rhodococcus kyotonensis by an enzyme promiscuity-based genome mining method was successfully cloned and functionally expressed in Escherichia coli. The whole cell biocatalyst harboring Rhky-ADH was biochemically characterized and was shown to be able to convert 2-Chloro-1-(3, 4-difluorophenyl) ethanone to (S)-2-Chloro-1-(3, 4-difluorophenyl) ethanol with more than 99 % enantiomeric excess (ee) and 99 % conversion. Our data showed that the optimum temperature and pH for Rhky-ADH were 25 °C and pH 8.0, respectively. The addition of NADH and an appropriate concentration of isopropanol enhanced the activity of Rhky-ADH, and 1 mM Mn2+ increased the enzyme activity by about 8 %. Substrate specificity experiments showed that Rhky-ADH had notable enzyme promiscuity and could reduce several ketones with high stereoselectivity. Our investigation on this novel enzyme adds another rare biocatalyst to the toolbox for producing chiral alcohols, which are widely used in the pharmaceutical industry.
- Hu, Junmei,Li, Gudong,Liang, Chaoqun,Shams, Saira,Zheng, Guojun,Zhu, Shaozhou
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- An iron variant of the Noyori hydrogenation catalyst for the asymmetric transfer hydrogenation of ketones
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We report the design of a new iron catalyst for the asymmetric transfer hydrogenation of ketones. This type of iron catalyst combines the structural characteristics of the Noyori hydrogenation catalyst (an axially chiral 2,2′-bis(phosphino)-1,1′-binaphthyl fragment and the metal-ligand bifunctional motif) and an ene(amido) group that can activate the iron center. After activation by 8 equivalents of potassiumtert-butoxide, (SA,RP,SS)-7aand (SA,RP,SS)-7bare active but nonenantioselective catalysts for the transfer hydrogenation of acetophenone and α,β-unsaturated aldehydes at room temperature in isopropanol. A maximum turnover number of 14480 was observed for (SA,RP,SS)-7ain the reduction of acetophenone. The right combination of the stereochemistry of the axially chiral 2,2′-bis(phosphino)-1,1′-binaphthyl group and the carbon-centered chiral amine-imine moiety in (SA,RP,RR)-7b′afforded an enantioselective catalyst for the preparation of chiral alcohols with moderate to good yields and a broad functional group tolerance.
- Huo, Shangfei,Wang, Qingwei,Zuo, Weiwei
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supporting information
p. 7959 - 7967
(2020/06/26)
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- KMnO4-catalyzed chemoselective deprotection of acetate and controllable deacetylation-oxidation in one pot
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A novel and efficient protocol for chemoselective deacetylation under ambient conditions was developed using catalytic KMnO4. The stoichiometric use of KMnO4 highlighted the dual role of a heterogeneous oxidant enabling direct access to aromatic aldehydes in one-pot sequential deacetylation-oxidation. The reaction employed an alternative solvent system and allowed the clean transformation of benzyl acetate to sensitive aldehyde in a single step while preventing over-oxidation to acids. Use of inexpensive and readily accessible KMnO4 as an environmentally benign reagent and the ease of the reaction operation were particularly attractive, and enabled the controlled oxidation and facile cleavage of acetate in a preceding step. This journal is
- Gurawa, Aakanksha,Kumar, Manoj,Rao, Dodla S.,Kashyap, Sudhir
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supporting information
p. 16702 - 16707
(2020/10/27)
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- Efficient Transfer Hydrogenation of Ketones using Methanol as Liquid Organic Hydrogen Carrier
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Herein, we demonstrate an efficient protocol for transfer hydrogenation of ketones using methanol as practical and useful liquid organic hydrogen carrier (LOHC) under Ir(III) catalysis. Various ketones, including electron-rich/electron-poor aromatic ketones, heteroaromatic and aliphatic ketones, have been efficiently reduced into their corresponding alcohols. Chemoselective reduction of ketones was established in the presence of various other reducible functional groups under mild conditions.
- Garg, Nidhi,Paira, Soumen,Sundararaju, Basker
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p. 3472 - 3476
(2020/05/29)
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- Green synthesis of chiral aromatic alcohols with Lactobacillus kefiri P2 as a novel biocatalyst
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Biocatalytic reduction is a very important field of research in synthetic organic chemistry. Herein, three different Lactic Acid Bacteria (LAB) strains were evaluated for their bioreduction potential using acetophenone as a model substrate. Among these strains, Lactobacillus kefiri P2 strain was determined as the best asymmetric reduction biocatalyst. Reaction optimization parameters such as reaction time, temperature, agitation speed and pH were systematically optimized using Lactobacillus kefiri P2 strain and model substrate acetophenone. Under these optimized reaction conditions, secondary chiral alcohols were obtained by bioreduction of various prochiral ketones with results up to 99% enantiomeric excess. In addition, the steric and electronic effects of substituents on enantioselectivity and conversion were evaluated. It has been shown that Lactobacillus kefiri P2 biocatalyst was an effective catalyst for asymmetric reduction. This method provides an environmentally friendly method for the synthesis of optically pure alcohols and an alternative approach to chemical catalysts.
- Bayda?, Yasemin,Dertli, Enes,?ahin, Engin
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p. 1035 - 1045
(2020/03/03)
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- Ketone Hydrogenation by Using ZnO?Cu(OH)Cl/MCM-41 with a Splash of Water: An Environmentally Benign Approach
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MCM-41-supported ZnO?Cu(OH)Cl nanoparticles were synthesized via an incipient wetness impregnation technique using zinc chloride and copper chloride salts as well as water at room temperature. The catalyst was characterized by powder X-ray diffraction (PXRD), infrared spectroscopy (IR), and TGA, whereas surface and morphological studies were performed by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The above studies revealed the incorporation of metal species into the pores of MCM-41, leading to a decrease in surface area of the nanoparticles that was found to be 239.079 m2/g. The substituents attached to the ketone determine the rate of the reaction, and the utilization of the green solvent ‘water’ astonishingly completes the hydrogenation reaction in 45 minutes at 40 °C with 100% conversion and 100% selectivity as analyzed by gas chromatography-mass spectrometry. Hence, ZnO?Cu(OH)Cl/MCM-41 nanoparticles with 2.46 wt% zinc and 6.39 wt% copper were demonstrated as an active catalyst for the reduction of ketones without using any gaseous hydrogen source making it highly efficient as well as environmentally and economically benign.
- Choudhary, Neha,Ghosh, Topi,Mobin, Shaikh M.
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p. 1339 - 1348
(2020/03/23)
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- Synthesis and characterization of Pd(II) and Ru(II) complexes of tetradentate N,N,N,N-(Diphosphinomethyl)amine ligands: Catalytic properties in transfer hydrogenation and heck coupling reactions
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– Tetradentate N,N,N,N-(diphosphinomethyl)amine ligands and their Pd(II) and Ru(II) complexes were synthesized under a nitrogen atmosphere using Schlenk technique. The synthesized ligands and the complexes were characterized with 1H- and 31P-NMR, FT-IR, TG/DTA, and elemental analysis techniques. Pd(II) Complexes were used as catalysts in Heck coupling reactions and Ru(II) complexes were tried in transfer hydrogenation reactions of acetophenone derivatives. According to the results, L4-Pd(II) complex showed the best catalytic activity in the Heck coupling reaction of p-methylbromobenzene with o-chlorostyrene. It was confirmed that the reduction of bromo and chloroacetophenones in all catalysts the conversions were higher. The results showed that Ru(II) complexes as efficient catalysts and up to 99percent conversions was occurred with bromo and chloro acetophenones in K2CO3/isopropyl alcohol media at 80 °C.
- Akkaya, Seda K??ker,Kele?, Mustafa,Uru?, Serhan
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- One-pot Chemoenzymatic Deracemisation of Secondary Alcohols Employing Variants of Galactose Oxidase and Transfer Hydrogenation
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Enantiomerically enriched chiral secondary alcohols serve as valuable building blocks for drug intermediates and fine chemicals. In this study the deracemisation of secondary alcohols to generate enantiomeric pure chiral alcohols has been achieved by combining enantio-selective enzymatic oxidation of a secondary alcohol, by a variant of GOase (GOase M3-5), with either non-selective ketone reduction via transfer hydrogenation (TH) or enantio-selective asymmetric transfer hydrogenation (ATH). Both the enzymatic oxidation system and the transition-metal mediated reduction system were optimised to ensure compatibility with each other resulting in a homogeneous reaction system. 1-(4-nitrophenyl)ethanol was generated with 99 % conversion and 98 % ee by the deracemisation method, and it has been extended to a series of other secondary alcohols with comparable results.
- Yuan, Bo,Debecker, Damien P.,Wu, Xiaofeng,Xiao, Jianliang,Fei, Qiang,Turner, Nicholas J.
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p. 6191 - 6195
(2020/10/15)
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- Group 6 Metal Carbonyl Complexes Supported by a Bidentate PN Ligand: Syntheses, Characterization, and Catalytic Hydrogenation Activity
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We report on the preparation of a series of phosphorus-nitrogen donor ligand complexes [M(CO)4(PN)], where M = Cr, Mo, W and PN is 2-(diphenylphosphino)ethylamine. The organometallic compounds were readily obtained upon reacting the respective metal hexacarbonyls with equimolar amounts of the pertinent ligand in the presence of tetraethylammonium bromide. The PN-ligated metal carbonyls were fully characterized by standard spectroscopic techniques and X-ray crystallography. The ability of the title compounds to function as homogeneous hydrogenation catalysts was probed in the reduction of acetophenone and benzaldehyde derivatives to yield the corresponding alcohols. The reaction setup was easily assembled by simply combining the components in the autoclave on the bench outside an inert-gas-operated glovebox system.
- Faust, Kirill,Topf, Christoph,Vielhaber, Thomas
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p. 4535 - 4543
(2020/12/23)
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- Highly Enantioselective Transfer Hydrogenation of Prochiral Ketones Using Ru(II)-Chitosan Catalyst in Aqueous Media
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Unprecedentedly high enantioselectivities are obtained in the transfer hydrogenation of prochiral ketones catalyzed by a Ru complex formed in situ with chitosan chiral ligand. This biocompatible, biodegradable chiral polymer obtained from the natural chitin afforded good, up to 86 % enantioselectivities, in the aqueous-phase transfer hydrogenation of acetophenone derivatives using HCOONa as hydrogen donor. Cyclic ketones were transformed in even higher, over 90 %, enantioselectivities, whereas further increase, up to 97 %, was obtained in the transfer hydrogenations of heterocyclic ketones. The chiral catalyst precursor prepared ex situ was examined by scanning electron microscopy, FT-mid- and -far-IR spectroscopy. The structure of the in situ formed catalyst was investigated by 1H NMR spectroscopy and using various chitosan derivatives. It was shown that a Ru pre-catalyst is formed by coordination of the biopolymer to the metal by amino groups. This precursor is transformed in water insoluble Ru-hydride complex following hydrogen donor addition. The practical value of the developed method was verified by preparing over twenty chiral alcohols in good yields and optical purities. The catalyst was applied for obtaining optically pure chiral alcohols at gram scale following a single crystallization.
- Sz?ll?si, Gy?rgy,Kolcsár, Vanessza Judit
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p. 820 - 830
(2018/12/13)
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- Lutidine-Based Chiral Pincer Manganese Catalysts for Enantioselective Hydrogenation of Ketones
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A series of MnI complexes containing lutidine-based chiral pincer ligands with modular and tunable structures has been developed. The complex shows unprecedentedly high activities (up to 9800 TON; TON=turnover number), broad substrate scope (81 examples), good functional-group tolerance, and excellent enantioselectivities (85–98 % ee) in the hydrogenation of various ketones. These aspects are rare in earth-abundant metal catalyzed hydrogenations. The utility of the protocol have been demonstrated in the asymmetric synthesis of a variety of key intermediates for chiral drugs. Preliminary mechanistic investigations indicate that an outer-sphere mode of substrate–catalyst interactions probably dominates the catalysis.
- Zhang, Linli,Tang, Yitian,Han, Zhaobin,Ding, Kuiling
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supporting information
p. 4973 - 4977
(2019/03/17)
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- Photoenzymatic Catalysis Enables Radical-Mediated Ketone Reduction in Ene-Reductases
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Flavin-dependent ene-reductases (EREDs) are known to stereoselectively reduce activated alkenes, but are inactive toward carbonyls. Demonstrated here is that in the presence of photoredox catalysts, these enzymes will reduce aromatic ketones. Mechanistic experiments suggest this reaction proceeds through ketyl radical formation, a reaction pathway that is distinct from the native hydride-transfer mechanism. Furthermore, this reactivity is accessible without modification of either the enzyme or cofactors, allowing both native and non-natural mechanisms to occur simultaneously. Based on control experiments, we hypothesize that binding to the enzyme active site attenuates the reduction potential of the substrate, enabling single-electron reduction. This reactivity highlights opportunities to access new catalytic manifolds by merging photoredox catalysis with biocatalysis.
- Sandoval, Braddock A.,Kurtoic, Sarah I.,Chung, Megan M.,Biegasiewicz, Kyle F.,Hyster, Todd K.
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supporting information
p. 8714 - 8718
(2019/05/28)
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- Towards practical earth abundant reduction catalysis: Design of improved catalysts for manganese catalysed hydrogenation
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Manganese catalysts derived from tridentate P,N,N ligands can be activated easily using weak bases for both ketone and ester hydrogenations. Kinetic studies indicate the ketone hydrogenations are 0th order in acetophenone, positive order in hydrogen and 1st order in the catalyst. This implies that the rate determining step of the reaction was the activation of hydrogen. New ligand systems with varying donor strength were studied and it was possible to make the hydrogen activation significantly more efficient; a catalyst displaying around a 3-fold increase in initial turn-over frequencies for the hydrogenation of acetophenone relative to the parent system was discovered as a result of these kinetic investigations. Ester hydrogenations and ketone transfer hydrogenation (isopropanol as reductant) are first order for both the substrate and catalysts. Kinetic studies also gained insight into catalyst stability and identified a working range in which the catalyst is stable throughout the catalytic reaction (and a larger working range where high yields can still be achieved). The new more active catalyst, combining an electron-rich phosphine with an electron-rich pyridine is capable of hydrogenating acetophenone using as little as 0.01 mol% catalyst at 65 °C. In all, protocols for reduction of 21 ketones and 15 esters are described.
- Widegren, Magnus B.,Clarke, Matthew L.
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p. 6047 - 6058
(2019/11/14)
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- Synthesis and Catalytic Activity of Iron Hydride Ligated with Bidentate N-Heterocyclic Silylenes for Hydroboration of Carbonyl Compounds
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We report the synthesis of a novel bidentate N-heterocyclic silylene (NHSi) ligand, N-(LSi:)-N-methyl-2-pyridinamine (1) (L = PhC(NtBu)2), and the first bischelate disilylene iron hydride, [(Si,N)(Si,C)Fe(H)(PMe3)] (2), and monosilylene iron hydride, [(Si,C)Fe(H)(PMe3)3] (2′), through Csp2-H activation of the NHSi ligand. Compounds 1 and 2 were fully characterized by spectroscopic methods and single-crystal X-ray diffraction analysis. Density functional theory calculations indicated the multiple-bond character of the Fe-Si bonds and the π back-donation from Fe(II) to the Si(II) center. Moreover, the strong donor character of ligand 1 enables 2 to act as an efficient catalyst for the hydroboration reaction of carbonyl compounds at room temperature. Chemoselective hydroboration is attained under these conditions. This might be the first example of hydroboration of ketones and aldehydes catalyzed by a silylene hydrido iron complex. A catalytic mechanism was suggested and partially experimentally verified.
- Qi, Xinghao,Zheng, Tingting,Zhou, Junhao,Dong, Yanhong,Zuo, Xia,Li, Xiaoyan,Sun, Hongjian,Fuhr, Olaf,Fenske, Dieter
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p. 268 - 277
(2019/01/21)
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- Chiral Frustrated Lewis Pairs Catalyzed Highly Enantioselective Hydrosilylations of Ketones
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A highly enantioselective Piers-type hydrosilylation of simple ketones was successfully realized using a chiral frustrated Lewis pair of tri-tert-butylphosphine and chiral diene-derived borane as catalyst. A wide range of optically active secondary alcohols were furnished in 80%—99% yields with 81%—97% ee's under mild reaction conditions.
- Liu, Xiaoqin,Wang, Qiaotian,Han, Caifang,Feng, Xiangqing,Du, Haifeng
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p. 663 - 666
(2019/05/21)
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- Enantiocomplementary decarboxylative hydroxylation combining photocatalysis and whole-cell biocatalysis in a one-pot cascade process
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Designing a green, highly efficient and stereoselective catalytic system to generate valuable enantioenriched products is a long-standing goal in green chemistry. Here, we report a one-pot cascade combining photocatalysts with (R)- or (S)-selective ketoreductases for the decarboxylative carbonylation of carboxylic acids and the subsequent bioreduction to generate valuable chiral alcohols. Using this approach, various chiral alcohols with complementary (R)- or (S)-configurations were prepared with good yields (up to 93%) and excellent stereoselectivity (up to 99% ee). Such a photochemo-enzymatic one-pot whole-cell process combines the advantages of both photocatalysts and enzyme catalysts and provides a mild, green, metal-free and highly stereoselective alternative in asymmetric decarboxylative hydroxylation reactions.
- Xu, Jian,Arkin, Mamatjan,Peng, Yongzhen,Xu, Weihua,Yu, Huilei,Lin, Xianfu,Wu, Qi
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p. 1907 - 1911
(2019/04/27)
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- Thermoregulated ionic liquid-coordinating ruthenium complexes for asymmetric hydrogenation of aromatic ketones
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This work presented the synthesis and characterization of new ionic liquid-coordinating ruthenium complexes. The resulting ruthenium complexes exhibited not only excellent thermoregulated phase-separation behavior but also highly catalytic activity and enantioselectivity for the asymmetric hydrogenation with molecular hydrogen. The thermoregulated ionic liquid catalyst was highly resistant to leaching and was recycled consecutively for six times without significant loss of catalytic activity and enantioselectivity. The presence of Ru–H species revealed that NH and a Ru–H unit, involved in the hydride transfer process, were of great importance in the present catalytic system.
- Tang, Guoping,Chen, Manyu,Fang, Jian,Xu, Zichen,Gong, Honghui,Peng, Qingpo,Hou, Zhenshan
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