- Rhodium-catalyzed hydroboration reactions with sulfur and nitrogen analogues of catecholborane
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Rhodium-catalyzed hydroboration of 1-octene and trans-4-octene with sulfur- and nitrogen analogues of catecholborane are demonstrated with the use of in situ 11B NMR spectroscopy. Our study shows that the sulfur- and nitrogen analogues are significantly less prone to disproportionation than catechol, which results in enhanced yields of the desired compounds. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
- Hadebe, Siphamandla W.,Robinson, Ross S.
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Read Online
- Reversal of Regioselectivity in Zinc-Dependent Medium-Chain Alcohol Dehydrogenase from Rhodococcus erythropolis toward Octanone Derivatives
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The zinc-dependent medium-chain alcohol dehydrogenase from Rhodococcus erythropolis (ReADH) is one of the most versatile biocatalysts for the stereoselective reduction of ketones to chiral alcohols. Despite its known broad substrate scope, ReADH only accepts carbonyl substrates with either a methyl or an ethyl group adjacent to the carbonyl moiety; this limits its use in the synthesis of the chiral alcohols that serve as a building blocks for pharmaceuticals. Protein engineering to expand the substrate scope of ReADH toward bulky substitutions next to carbonyl group (ethyl 2-oxo-4-phenylbutyrate) opens up new routes in the synthesis of ethyl-2-hydroxy-4-phenylbutanoate, an important intermediate for anti-hypertension drugs like enalaprilat and lisinopril. We have performed computer-aided engineering of ReADH toward ethyl 2-oxo-4-phenylbutyrate and octanone derivatives. W296, which is located in the small binding pocket of ReADH, sterically restricts the access of ethyl 2-oxo-4-phenylbutyrate, octan-3-one or octan-4-one toward the catalytic zinc ion and thereby limits ReADH activity. Computational analysis was used to identify position W296 and site-saturation mutagenesis (SSM) yielded an improved variant W296A with a 3.6-fold improved activity toward ethyl 2-oxo-4-phenylbutyrate when compared to WT ReADH (ReADH W296A: 17.10 U/mg and ReADH WT: 4.7 U/mg). In addition, the regioselectivity of ReADH W296A is shifted toward octanone substrates. ReADH W296A has a more than 16-fold increased activity toward octan-4-one (ReADH W296A: 0.97 U/mg and ReADH WT: 0.06 U/mg) and a more than 30-fold decreased activity toward octan-2-one (ReADH W296A: 0.23 U/mg and ReADH WT: 7.69 U/mg). Computational and experimental results revealed the role of position W296 in controlling the substrate scope and regiopreference of ReADH for a variety of carbonyl substrates.
- Dhoke, Gaurao V.,Ensari, Yunus,Hacibaloglu, Dinc Yasat,G?rtner, Anna,Ruff, Anna Jo?lle,Bocola, Marco,Davari, Mehdi D.
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- The effects of metals and ligands on the oxidation of n-octane using iridium and rhodium “PNP” aminodiphosphine complexes
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Ir and Rh “PNP” complexes with different ligands are utilized for the oxidation of n-octane. Based on the obtained conversion, selectivity, and the characterized recovered catalysts, it is found that the combination of Ir and the studied ligands does not promote the redox mechanism that is known to result in selective formation of oxo and peroxo compounds [desired species for C(1) activation]. Instead, they support a deeper oxidation mechanism, and thus higher selectivity for ketones and acids is obtained. In contrast, these ligands seem to tune the electron density around the Rh (in the Rh-PNP complexes), and thus result in a higher n-octane conversion and improved selectivity for the C(1) activated products, with minimized deeper oxidation, in comparison to Ir-PNP catalysts.
- Naicker, Dunesha,Alapour, Saba,Friedrich, Holger B
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p. 282 - 289
(2020/12/01)
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- Efficient and region-selective conversion of octanes to epoxides under ambient conditions: Performance of tri-copper catalyst, [Cu3I(L)]+1 (L=7-N-Etppz)
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In this paper, is described the conversion of the octane group of hydrocarbons into industrially important epoxides using tri-copper catalyst, [Cu3I(L)]+1 (L=7-N-Etppz). The role of hydrogen peroxide as a sacrificial oxygen donor during catalytic conversion to epoxides has been investigated. The performance of the catalyst has been evaluated in terms of turnover numbers (TON) and turnover frequencies (TOF) reported in this article.
- Krupadam, Reddithota J.,Nagababu, Penumaka,Paul, Perala Sudheer,Reddy, Thatiparthi Byragi
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p. 742 - 745
(2021/09/28)
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- Flexible pincer backbone revisited: CuSNS complexes as efficient catalysts in paraffin oxidation
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New Cu(II) complexes containing a set of tridentate hybrid SNS ligands were synthesised and fully characterised by IR, HRMS, elemental analysis and single-crystal X-ray diffraction. The complexes with the general formula Cu[bis(Rthioethyl)phenylamine]Cl2 (1); [R = methyl (a); ethyl (b); butyl (c); cyclohexyl (d) and t-butyl (e)] exhibited five-coordinate trigonal bipyramidal geometry around each Cu(II) centre in the solid-state with the S-donor atoms occupying the axial positions. However, complex 1b crystallised as a dimer bridged through a cuprate anion denoted as [1b(μ-CuCl4)1b]. Their application as catalysts in the oxidation of n-octane with hydrogen peroxide (H2O2) as an oxidant gave high substrate conversions to C-8 oxygenate products, mainly octanols, after reduction with PPh3. Notably, complex 1d produced the highest yield of 57% in 1 h reaction time at a catalyst concentration of 1 mol%. In general, high turnover numbers (2830–3180) were recorded for the 1/H2O2 catalytic systems with substantially high combined selectivity of 22–27% to 1-octanol and octanoic acid, which are the more desired products of n-octane oxidation resulting from its terminal carbon (C(1)) activation. The high activity of the catalysts is attributed to metal–ligand cooperative catalysis involving CuII-OOH intermediates as the active species modulated by the tridentate SNS ligands. In comparison with related complexes bearing N-donor atoms, the excellent catalytic performance of these series of CuSNS complexes highlights the critical role of the phenylamine N-donor atom.
- Bala, Muhammad D.,Friedrich, Holger B.,Soobramoney, Lynette
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supporting information
(2021/07/16)
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- Biocatalytic synthesis of non-vicinal aliphatic diols
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Biocatalysts are receiving increased attention in the field of selective oxyfunctionalization of C-H bonds, with cytochrome P450 monooxygenases (CYP450s), and the related peroxygenases, leading the field. Here we report on the substrate promiscuity of CYP505A30, previously characterized as a fatty acid hydroxylase. In addition to its regioselective oxyfunctionalization of saturated fatty acids (ω-1-ω-3 hydroxylation), primary fatty alcohols are also accepted with similar regioselectivities. Moreover, alkanes such as n-octane and n-decane are also readily accepted, allowing for the production of non-vicinal diols through sequential oxygenation. This journal is
- Ebrecht, Ana C.,Aschenbrenner, Jasmin C.,Smit, Martha S.,Opperman, Diederik J.
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supporting information
p. 439 - 445
(2021/01/29)
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- Application of new Ru (II) pyridine-based complexes in the partial oxidation of n-octane
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Tridentate and bidentate Ru (II) complexes were prepared through reaction of four pyridine-based ligands: pyCH2N(R)CH2py {R = propyl, tert-butyl, cyclohexyl and phenyl; py = pyridine} with the [(η6-C6H6)Ru(μ-Cl)Cl]2 dimer. Crystal structures of the new terdentate Ru (II) complexes [Ru{pyCH2N(R)CH2py}C6H6](PF6)2 (R = C3H7 (1), C (CH3)3 (2), C6H11 (3) and the bidentate Ru (II) complex [Ru{pyCH2N(R)}C6H6]PF6 (R = C6H5 (4)) are reported. It was found that complexes 1, 2, 3 and 4 crystallised as mono-metallic species, with a piano stool geometry around each Ru centre. All complexes were active in the selective oxidation of n-octane using t-BuOOH and H2O2 as oxidants. Complexes 2 and 4 reached a product yield of 12% with t-BuOOH as oxidant, however, superior yields (23–32%) were achieved using H2O2 over all systems. The selectivity was predominantly towards alcohols (particularly 2-octanol) over all complexes using t-BuOOH and H2O2 after reduction of the formed alkylhydroperoxides in solution by PPh3. High TONs of up to 2400 were achieved over the Ru/H2O2 systems.
- Chanerika, Revana,Friedrich, Holger B.,Shozi, Mzamo L.
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- Synthesis of Co(II) NNN-pyridine based complexes and their activity in the partial oxidation of n-octane
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A series of four NNN-pyridine based ligands of the general form: pyCH2N(R)CH2py {R = propyl, tert-butyl, cyclohexyl and phenyl; py = pyridine} were synthesised and characterised. Complexation of each ligand to CoCl2?6H2O afforded new Co(II) complexes [Co{pyCH2N(R)CH2py}Cl2] (R = C3H7 (1), C(CH3)3 (2), C6H11 (3) and C6H5 (4)). Single crystal X-ray diffraction data confirmed that complex 1 crystallised as a mononuclear unit and was characterised by a distorted trigonal bipyramidal arrangement of ligands around Co. As catalysts in the oxidation of n-octane using t-BuOOH as oxidant, 2 (10% product yield) was found to be most efficient and the selectivity over 1–4 was predominantly towards 2-octanol, after reduction of alkylhydroperoxides by PPh3. All catalysts were significantly more active in the activation of n-octane using hydrogen peroxide, with a yield of 45% observed over catalyst 3. Furthermore, with H2O2, all catalysts produced a high concentration of alkylhydroperoxides, with catalyst 4 giving up to 91% alcohols after workup. TONs of up to 1100 were achieved over the Co/H2O2 systems.
- Chanerika, Revana,Friedrich, Holger B.,Shozi, Mzamo L.
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- Synthesis, structural characterization and C–H activation property of a tetra-iron(III) cluster
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A non-heme tetra-iron cluster, [Fe4 III(μ-O)2(μ-OAc)6(2,2′-bpy)2(H2O)2](NO3 ?)(OH?) (1), [OAc = acetate; 2,2′-bpy = 2,2′-bipyridine] containing oxido- and acetato-bridges was synthesized and structurally characterized by different spectroscopic methods including single crystal X-ray diffraction studies. X-ray crystal structure analysis of 1 revealed that tetra-iron complex was crystallized in monoclinic system with C2/c space group. Each of the Fe centres in 1 was found to exist in octahedral geometry and interconnected by oxido- and acetato-bridges. Bond valence sum (BVS) calculation recommended the existence of iron centres in +3 oxidation state. Variable temperature magnetic measurement authenticated the dominating antiferromagnetic ordering among the iron centres in the solid state of 1. This tetra-iron cluster was also evaluated as an efficient catalytic system towards the oxidation of both linear & cyclic alkanes without production of primary C–H bond oxidation products. Oxidation of secondary C–H bonds attested the formation of both the corresponding alcohols & ketones in 27–900 TONs. The tetra-iron catalytic system with Alcohol/Ketone values 0.2–1.7 indicated the involvement of freely diffusing carbon-centered radicals rather than metal based oxidant.
- Dey, Dhananjay,Patra, Moumita,Al-Hunaiti, Afnan,Yadav, Hare Ram,Al-mherat, Afrah,Arar, Sharif,Maji, Milan,Choudhury, Angshuman Roy,Biswas, Bhaskar
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p. 220 - 226
(2019/01/05)
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- Symmetric triazolylidene Ni(II) complexes applied as oxidation catalysts
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A set of related Ni(II) complexes of N-heterocyclic carbene ligands (NHC) [trans-X2Ni(NHC)2] (X = Cl, I) bearing linear straight chain alkyl wingtip substituents have been synthesised and fully characterised. Single crystal XRD data revealed symmetrically aligned Ni(II) centres within square planar coordination of trans halide, trans NHC ligands. The complexes were used for the catalytic oxidation of alkanes under mild conditions in conjunction with tert-butyl hydroperoxide as an oxidant. Under optimised reaction conditions, the catalytic results pointed to good activities of circa 15% and 19% for cyclohexane and n-octane respectively. Furthermore, the catalytic systems are shown to be very efficient for the oxidation of linear alcohols to corresponding ketones.
- Mncube, Siyabonga G.,Bala, Muhammad D.
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p. 467 - 473
(2018/11/06)
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- Flexible SNS pincer complexes of copper: Synthesis, structural characterisation and application in n-octane oxidation
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Two new tridentate SNS ligands based on a flexible, straight chain amine backbone were prepared and in combination with three related but previously reported ligands were reacted with CuCl2 to yield new tridentate pincer-type copper(II) complexes. The molecular structures of the new ligands bis(cyclohexylthioethyl)methylamine (L1d), bis(t-butylthioethyl)methylamine (L1e), and all the complexes Cu[bis(Rthioethyl)methylamine]Cl2 (1) where R = methyl (a); ethyl (b); butyl (c); cyclohexyl (d) and t-butyl (e); were confirmed by a range of spectroscopic and analytical techniques. Single crystal X-ray diffraction analysis determined the solid-state structures of the salt of L1e and the complexes. Complexes 1a-e all exhibited five-coordinate ligand geometry around each Cu(II) centre defined by the tridentate SNS and two chlorido donors. The complexes were applied as catalysts in the oxidation of n-octane using t-butyl hydroperoxide and hydrogen peroxide (H2O2) as oxidants. The H2O2 based systems yielded up to 36% conversion of n-octane to C-8 oxygenates with very high alcohol selectivity of up to 78%.
- Soobramoney, Lynette,Bala, Muhammad D.,Friedrich, Holger B.,Pillay, Michael N.
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- Utilisation of new NiSNS pincer complexes in paraffin oxidation
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Two series of closely related SNS pincer ligands (L) were synthesised with the major structural variation on the nitrogen backbone containing either the methyl [L = (RSCH2CH2)2NMe: where R = Me (1), Et (2), Bu (3)] or the phenyl [L = (RSCH2CH2)2NPh: where R = Me (4), Et (5), Cy (6)] functional group. When ligands 1–3 were complexed to Ni by reaction with Ni(DME)Cl2 (DME = dimethoxyethane), they respectively yielded three new cationic dimeric [LNi(μ-Cl)3NiL]+ complexes (7–9), whilst ligands 4–6 on reaction with Ni(PPh3)2Br2 respectively yielded neutral mononuclear (LNiBr2) complexes 10–12. All the new compounds were characterised by IR, HRMS, elemental analysis and in addition, single crystal X-ray diffraction for complexes 9–12. X-ray structural data of 9 revealed an unusual three chlorido-bridged Ni dimer with the SNS ligand coordinated in a facial binding mode to the two pseudo-octahedral Ni centres. Molecular structures of complexes 10, 11 and 12 each displayed five-coordinate distorted trigonal bipyramidal geometry around the nickel(II) metal centres. When utilised as catalysts in the tert-butyl hydroperoxide oxidation of n-octane, all the complexes showed activity to mainly products of internal carbon activation (octanones and secondary octanols) with 11 as the most active (10% total substrate to oxygenates yield), whereas 10 was the least active, but most selective towards alcohols (alcohol/ketone = 2.13).
- Soobramoney, Lynette,Bala, Muhammad D.,Friedrich, Holger B.
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- OPEN-FLASK HYDROBORATION AND THE USE THEREOF
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The present disclosure generally relates to a process for hydroboration of an alkene or alkyne using ammonia borane (AB). In particular, the present invention relates to hydroboration of an alkene or alkyne in the presence of air or moisture, and a clean process for facile preparation of an alcohol by oxidizing the organoborane so formed with hydrogen peroxide. The products, including aminodialkylboranes, ammonia trialkylborane complexes, as well as various alcohols so prepared, are within the scope of this disclosure.
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Paragraph 0046; 0049; 0059; 0060; 0061
(2018/03/25)
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- Direct Conversion of Alcohols into Alkenes by Dehydrogenative Coupling with Hydrazine/Hydrazone Catalyzed by Manganese
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We have developed unprecedented methods for the direct transformation of primary alcohols to alkenes in the presence of hydrazine, and for the synthesis of mixed alkenes by the reaction of alcohols with hydrazones. The reactions are catalyzed by a manganese pincer complex and proceed in absence of added base or hydrogen acceptors, liberating dihydrogen, dinitrogen, and water as the only byproducts. The proposed mechanism, based on preparation of proposed intermediates and control experiments, suggests that the transformation occurs through metal–ligand cooperative N?H activation of a hydrazone intermediate.
- Das, Uttam Kumar,Chakraborty, Subrata,Diskin-Posner, Yael,Milstein, David
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supporting information
p. 13444 - 13448
(2018/09/14)
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- Interplay between H-bonding and interpenetration in an aqueous copper(ii)-aminoalcohol-pyromellitic acid system: self-assembly synthesis, structural features and catalysis
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Two new copper(ii) coordination compounds, [Cu(H1.5mdea)2]2(H2pma) (1a) and [{Cu2(μ-Hmdea)2}2(μ4-pma)]n·2nH2O (1b), were self-assembled at different temperatures from the same multicomponent reaction system, comprising copper(ii) nitrate, N-methyldiethanolamine (H2mdea), pyromellitic acid (H4pma), and potassium hydroxide. Products 1a and 1b were isolated as microcrystalline solids and fully characterized and their structures were established by single-crystal X-ray diffraction. Compound 1a features the bis-aminoalcohol(ate) monocopper(ii) units and H2pma2? anions that are multiply interconnected by strong H-bonds into a firm 2D H-bonded layer. Compound 1b reveals the bis-aminoalcoholate dicopper(ii) motifs that are interlinked by the μ4-pma4? spacers into a 3D + 3D interpenetrated metal-organic framework. From a topological perspective, both networks of 1a and 1b are uninodal and driven by similar 4-connected H2pma2? or pma4? nodes, but result in distinct sql and dia topologies, respectively. Compound 1a was applied as an efficient catalyst for two model cycloalkane functionalization reactions: (1) oxidation by H2O2 to form cyclic alcohols and ketones and (2) hydrocarboxylation by CO/H2O and S2O82? to form cycloalkanecarboxylic acids. The substrate scope, effects of various reaction parameters, selectivity and mechanistic features were also investigated.
- Fernandes, Tiago A.,Kirillova, Marina V.,André, Vania,Kirillov, Alexander M.
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p. 16674 - 16683
(2018/12/05)
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- Ligand-free nickel-catalyzed semihydrogenation of alkynes with sodium borohydride: A highly efficient and selective process for: Cis -alkenes under ambient conditions
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We report a low-cost and efficient catalytic system, involving in situ generated ligand-free Ni NPs, methanol and sodium borohydride, for the semihydrogenation of alkynes under ambient conditions. This catalytic system exhibits remarkably high activity, satisfactory cis-selectivity for internal alkynes, good stability and general applicability.
- Wen, Xin,Shi, Xiaozhen,Qiao, Xianliang,Wu, Zhilei,Bai, Guoyi
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supporting information
p. 5372 - 5375
(2017/07/06)
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- Base metal Schiff base complexes applied as catalysts for the oxidation of n-octane
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The catalytic oxidation of n-octane to value-added oxygenates has been studied with a series of salen-type complexes of iron. The four iron Schiff base complexes N,N′-bis(salicylidene)-L-iron(III) chloride [L?=?1,2-phenylenediamine (5); ethylenediamine (6); propylenediamine (7) and butylenediamine (8)] were synthesised by variation of the bridging diamine backbone. All the complexes are fully characterised and the crystal structure of 7 is for the first time reported as a centrosymmetric dimer observed to crystallise in the triclinic P1 ̄ system. The application of 5–8 in this oxidation reaction represents a rare example of the systematic use of iron-salen complexes for the liquid-phase functionalisation of Csp3–H bonds of straight chain alkanes. All catalysts displayed activity with H2O2 and TBHP as oxidants that resulted in a mixture of oxygenated products dominated by the ketones (2-, 3- and 4-octanones). Observed trends and variations in catalytic activities of the complexes is related to differences in chemical/structural features and changes in reaction conditions. A detailed analysis of selectivity parameters of the complexes to the variety of oxygenates is also presented and rationalised.
- Kadwa, Ebrahim,Friedrich, Holger B.,Bala, Muhammad D.
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p. 112 - 117
(2017/04/27)
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- Solvent effects in hydrodeoxygenation of furfural-acetone aldol condensation products over Pt/TiO2 catalyst
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The solvent effects on hydrodeoxygenation (HDO) of 4-(2-furyl)-3-buten-2-one (F-Ac) over Pt/TiO2 catalyst were investigated at T = 200 °C and P(H2) = 50 bar. The initial reactant is the main product of aldol condensation between furfural and acetone, which constitutes a promising route for the production of bio-based chemicals and fuels. A sequence of experiments was performed using a selection of polar solvents with different chemical natures: protic (methanol, ethanol, 1-propanol, 2-propanol, 1-pentanol) and aprotic (acetone, tetrahydrofuran (THF), n,n-dimethylformamide (DMF)). In case of protic solvents, a good correlation was found between the polarity parameters and conversion. Consequently, the highest hydrogenation rate was observed when 2-propanol was used as a solvent. In contrast, the hydrogenation activity in presence of aprotic solvents was related rather to solvent-catalyst interactions. Thus, the initial hydrogenation rate declined in order Acetone > THF > DMF, i.e. in accordance with the increase in the nucleophilic donor number and solvent desorption energy. Regarding the product distribution, a complex mixture of intermediates was obtained, owing to the successive hydrogenation (aliphatic C[dbnd]C, furanic C[dbnd]C and ketonic C[dbnd]O bonds), ring opening (via C[sbnd]O hydrogenolysis) and deoxygenation reactions. Based on the proposed reaction scheme for the conversion of F-Ac into octane, the influence of the studied solvents over the cascade catalytic conversion is discussed. A significant formation of cyclic saturated compounds such as 2-propyl-tetrahydropyran and 2-methyl-1,6-dioxaspiro[4,4]nonane took place via undesirable side reactions of cyclization and isomerization. The best catalytic performance was found when using acetone and 2-propanol as solvents, achieving significant yields of 4-(2-tetrahydrofuryl)-butan-2-ol (28.5–40.4%) and linear alcohols (6.3–10.4%). The better performance of these solvents may be associated with a lower activation energy barrier for key intermediate products, due to their moderate interaction with the reactant and the catalyst. In case of methanol and DMF, undesired reactions between the reactant and the solvent took place, leading to a lower selectivity towards the targeted hydrodeoxygenated products.
- Ramos, Rubén,Ti?ler, Zdeněk,Kikhtyanin, Oleg,Kubi?ka, David
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p. 174 - 183
(2016/12/06)
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- Oxidation of Alkanes by Periodate Using a MnV Nitrido Complex as Catalyst
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The design of catalytic systems that can selectively oxidize unactivated C?H bonds under mild conditions is a challenge to chemists. We report here that the manganese(V) nitrido complex [MnV(N)(CN)4]2? is a highly efficient catalyst for the oxidation of alkanes by periodate (IO4 ?) at ambient conditions. Excellent yields of alcohols and ketones (>95 %) are obtained with a maximum turnover number (TON) of 3000.
- Ma, Li,Chen, Lingjing,Lau, Tai-Chu
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p. 2846 - 2848
(2016/10/25)
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- ALKANE OXIDATION BY MODIFIED HYDROXYLASES
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This invention relates to modified hydroxylases. The invention further relates to cells expressing such modified hydroxylases and methods of producing hydroxylated alkanes by contacting a suitable substrate with such cells.
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Paragraph 0329
(2016/02/16)
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- A non-dissociative open-flask hydroboration with ammonia borane: Ready synthesis of ammonia-trialkylboranes and aminodialkylboranes
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Under open-flask conditions, ammonia borane hydroborates olefins in refluxing tetrahydrofuran. Unlike conventional hydroboration, the Lewis base (ammonia) is not dissociated from the boron center. Terminal alkenes selectively provide ammonia-trialkylborane complexes. On the other hand, internal alkenes afford aminodialkylboranes via a metal-free hydroboration-dehydrogenation sequence. Alkaline hydrogen peroxide oxidation of the products provides the corresponding alcohols in high yields.
- Ramachandran, P. Veeraraghavan,Drolet, Michael P.,Kulkarni, Ameya S.
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supporting information
p. 11897 - 11900
(2016/10/09)
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- Cytochrome P450 oxygenases
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Nucleic acids encoding cytochrome P450 variants are provided. The cytochrome P450 variants of have a higher alkane-oxidation capability, alkene-oxidation capability, and/or a higher organic-solvent resistance than the corresponding wild-type or parent cytochrome P450 enzyme. A preferred wild-type cytochrome P450 is cytochrome P450 BM-3. Preferred cytochrome P450 variants include those having an improved capability to hydroxylate alkanes and epoxidate alkenes comprising less than 8 carbons, and have amino acid substitutions corresponding to V78A, H236Q, and E252G of cytochrome P450 BM-3. Preferred cytochrome P450 variants also include those having an improved hydroxylation activity in solutions comprising co-solvents such as DMSO and THF, and have amino acid substitutions corresponding to T235A, R471A, E494K, and S1024E of cytochrome P450 BM-3.
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Page/Page column 25; 26
(2016/05/24)
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- Revisiting cytochrome P450-mediated oxyfunctionalization of linear and cyclic alkanes
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Cytochrome P450 monooxygenases (CYPs) of the CYP153 family catalyse terminal hydroxylation of n-alkanes. Alkane hydroxylating mutants of self-sufficient CYP102A1 have also been described. We evaluated two CYP153s (a three-component system and a fused self-sufficient CYP), wildtype CYP102A1 and nine CYP102A1 mutants, for the conversion of three cycloalkanes (C6, C7 and C8) and three n-alkanes (C6, C8 and C10) using whole cells (WCs) and crude cell-free extracts (CFEs). The aim was to identify substrate-enzyme combinations that give high product titres and space-time yields (STYs). Comparisons were made using total turnover numbers (TTNs) and turnover frequencies (TOFs) to normalize for CYP expression. Reactions were carried out using high enzyme and substrate concentrations compatible with high STYs. Under these conditions CYP102A1 and the double R47L,Y51F mutant, although not regioselective, performed better on all substrates in terms of product titres over 8 h, and thus STYs and TTNs, than heavily mutated variants that have been reported to give very high TOFs. CYP153A6, with its ferredoxin (Fdx) and ferredoxin reductase (FdR), emerged as the superior catalyst for conversion of n-alkanes. In addition to its excellent regioselectivity it also gave the highest final product titres and STYs in WC conversions of hexane and octane. Interaction with FdR and Fdx initially limited performance in CFEs, but with additional FdR and Fdx gave 1-octanol titres of 50 mmol·LBRM-1 and TTNs exceeding 12,000 over 18 h, rivalling results reported with self-sufficient CYPs. Selecting biocatalysts for application requires caution, since experimental conditions such as amount of substrate added and solubility as well as cofactor dependence and regeneration can have a profound effect on catalyst performance, while stability and efficiency with regard to cofactor usage (coupling efficiency) are at least as important as TOFs when high product titres and STYs are the target.
- Pennec, Aliz,Jacobs, Cheri L.,Opperman, Diederik J.,Smit, Martha S.
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supporting information
p. 118 - 130
(2015/01/30)
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- Cobalt aminodiphosphine complexes as catalysts in the oxidation of n-octane
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Two types of cobalt aminodiphosphine complexes have been synthesized and characterized by IR spectroscopy, elemental analyses and single crystal X-ray diffraction. These are [Ph2PN(R)PPh2]CoCl2, 1 and [Ph2P(CH2)2N(R)(CH2)2PPh2]CoCl2, 2 where R = C6H11 (a); C5H11 (b); C3H7 (c). The functional groups on the nitrogen atom (R) were varied from a cyclohexyl ring, to n-pentyl alkyl chain, to an iso-propyl branched substituent. Complexes 2a and 2c were analyzed using single crystal X-ray diffraction. The geometry around the metal centers in 2a and 2c were distorted tetrahedral. All the complexes showed good activity as catalysts for the oxidation of n-octane using tert-butyl hydroperoxide (TBHP) as the oxidant. The complex bearing the flexible ligand backbone with the cyclohexyl substituent on the nitrogen atom was the most active and showed high selectivity towards ketones with 2-octanone being the dominant product.
- Naicker, Dunesha,Friedrich, Holger B.,Omondi, Bernard
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p. 63123 - 63129
(2015/08/06)
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- Catalytic Oxidation of Alkanes and Alkenes by H2O2 with a μ-Oxido Diiron(III) Complex as Catalyst/Catalyst Precursor
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A new μ-oxo diiron(III) complex of the lithium salt of the pyridine-based unsymmetrical ligand 3-[(3-{[bis(pyridin-2-ylmethyl)amino]methyl}-2-hydroxy-5-methylbenzyl)(pyridin-2-ylmethyl)amino]propanoate (LiDPCPMPP), [Fe2(μ-O)(LiDPCPMPP)2](ClO4)2, has been synthesized and characterized. The ability of the complex to catalyze oxidation of several alkanes and alkenes has been investigated by using CH3COOH/H2O2 (1:1) as an oxidative system. Moderate activity in cyclohexane oxidation (TOF = 33 h-1) and good activity in cyclohexene oxidation (TOF = 72 h-1) were detected. Partial retention of configuration (RC = 53%) in cis- and trans-1,2-dimethylcyclohexane oxidation, moderate 3/2 selectivity (4.1) in adamantane oxidation, and the observation of a relatively high kinetic isotope effect for cyclohexane oxidation (KIE = 3.27) suggest partial metal-based oxidation, probably in tandem with free-radical oxidation. Low-temperature UV/Vis spectroscopy and mass spectrometric studies in the rapid positive detection mode indicate the formation of a transient peroxido species, [Fe2(O)(O2)(LiDPCPMPP)2]2+, which might be an intermediate in the metal-based component of the oxidation process. A μ-oxido diiron(III) complex, [Fe2(μ-O)(LiDPCPMPP)2](ClO4)2, was synthesized and characterized. This complex was used as catalyst in C-H bond oxidation with CH3COOH-H2O2 as chemical oxidant. Reactivity studies indicate that the oxidation process goes through a metal-based mechanism concomitant with a radical process.
- Das, Biswanath,Al-Hunaiti, Afnan,Haukka, Matti,Demeshko, Serhiy,Meyer, Steffen,Shteinman, Albert A.,Meyer, Franc,Repo, Timo,Nordlander, Ebbe
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p. 3590 - 3601
(2015/08/06)
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- Regulation of Iron-Catalyzed Olefin Hydroboration by Ligand Modifications at a Remote Site
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An amide-derived N,N,N-Fe(II) complex catalyzes the hydroboration of alkenes at room temperature. Alkylation of a remote site on the ligand backbone was used as a late-stage modification to provide a more electrophilic complex as determined by electrochemical studies. The alkylated variant, compared to the parent complex, catalyzes olefin hydroboration with an increased reaction rate and exhibits distinct regioselectivity for internal alkene hydroboration. (Figure Presented).
- Tseng, Kuei-Nin T.,Kampf, Jeff W.,Szymczak, Nathaniel K.
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p. 411 - 415
(2015/04/27)
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- Co-oxidation of octane and benzaldehyde using molecular oxygen with Au-Pd/carbon prepared by sol-immobilisation
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The selective oxidation of linear alkanes with molecular oxygen under mild conditions remains a challenging topic in the field of catalysis. In this study we investigate the co-oxidation of C-H bonds in substrates with different relative reactivities, the aim being to couple the oxidised products in situ to form the corresponding esters. Initial attempts were made to co-oxidise octane with toluene to form octyl benzoate using Au-Pd catalysts. During the study the oxidation of octane in the presence of benzaldehyde, an oxidation product of toluene, was also investigated in order to demonstrate the potential feasibility of the reaction. This work summarises our attempts to show whether a co-oxidation system could be an effective way to oxidise linear alkanes.
- Peneau, Virginie,Shaw, Greg,Freakley, Simon J.,Forde, Michael M.,Dimitratos, Nikolaos,Jenkins, Robert L.,Taylor, Stuart H.,Hutchings, Graham J.
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p. 3953 - 3959
(2015/08/03)
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- Highly efficient alkane oxidation catalyzed by [MnV(N)(CN) 4]2-. Evidence for [MnVII(N)(O)(CN) 4]2- as an active intermediate
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The oxidation of various alkanes catalyzed by [MnV(N)(CN) 4]2- using various terminal oxidants at room temperature has been investigated. Excellent yields of alcohols and ketones (>95%) are obtained using H2O2 as oxidant and CF3CH 2OH as solvent. Good yields (>80%) are also obtained using (NH4)2[Ce(NO3)6] in CF 3CH2OH/H2O. Kinetic isotope effects (KIEs) are determined by using an equimolar mixture of cyclohexane (c-C6H 12) and cyclohexane-d12 (c-C6D12) as substrate. The KIEs are 3.1 ± 0.3 and 3.6 ± 0.2 for oxidation by H2O2 and Ce(IV), respectively. On the other hand, the rate constants for the formation of products using c-C6H12 or c-C6D12 as single substrate are the same. These results are consistent with initial rate-limiting formation of an active intermediate between [Mn(N)(CN)4]2- and H2O2 or CeIV, followed by H-atom abstraction from cyclohexane by the active intermediate. When PhCH2C(CH3)2OOH (MPPH) is used as oxidant for the oxidation of c-C6H12, the major products are c-C6H11OH, c-C6H10O, and PhCH2C(CH3)2OH (MPPOH), suggesting heterolytic cleavage of MPPH to generate a Mn=O intermediate. In the reaction of H2O2 with [Mn(N)(CN)4]2- in CF 3CH2OH, a peak at m/z 628.1 was observed in the electrospray ionization mass spectrometry, which is assigned to the solvated manganese nitrido oxo species, (PPh4)[Mn(N)(O)(CN)4] -·CF3CH2OH. On the basis of the experimental results the proposed mechanism for catalytic alkane oxidation by [MnV(N)(CN)4]2-/ROOH involves initial rate-limiting O-atom transfer from ROOH to [Mn(N)(CN)4]2- to generate a manganese(VII) nitrido oxo active species, [MnVII(N)(O) (CN)4]2-, which then oxidizes alkanes (R'H) via a H-atom abstraction/O-rebound mechanism. The proposed mechanism is also supported by density functional theory calculations.
- Ma, Li,Pan, Yi,Man, Wai-Lun,Kwong, Hoi-Ki,Lam, William W.Y.,Chen, Gui,Lau, Kai-Chung,Lau, Tai-Chu
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p. 7680 - 7687
(2014/06/10)
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- Coordination chemistry of Co complexes containing tridentate SNS ligands and their application as catalysts for the oxidation of n-octane
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The selective oxidation of saturated hydrocarbons to terminal oxygenates under mild catalytic conditions has remained a centuries long challenge in chemical catalysis. In an attempt to address this challenge, two series of tridentate donor ligands {2,6-bis(RSCH2)pyridine and bis(RSCH2CH2)amine [R = alkyl, aryl]} and their respective cobalt complexes {Co[2,6-bis(RSCH2)pyridine]Cl2 and Co[bis(RSCH2CH2)amine]Cl2} were synthesized and characterized. Crystal structures of Co[2,6-bis(RSCH2)pyridine]Cl2 [R = -CH3 (1), -CH2CH3 (2), -CH2CH2CH2CH3 (3) and -C6H5 (4)] are reported in which 1 crystallized as a homo-bimetallic dimer that incorporated two bridging chloride atoms in an octahedral geometry around each cobalt center, while 2, 3 and 4 crystallized as mono-metallic species characterized by trigonal bipyramidal arrangement of ligands around each cobalt center. As catalysts for the homogeneous selective oxidation of n-octane, the catalysts yielded ketones as the dominant products with a selectivity of ca. 90% for the most active catalyst Co[bis(CH2CH2SCH2CH2)amine]Cl2 (6) at a total n-octane conversion of 23%. Using tert-butyl hydroperoxide (TBHP) as an oxidant, optimization of reaction conditions is also reported.
- Soobramoney, Lynette,Bala, Muhammad D.,Friedrich, Holger B.
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p. 15968 - 15978
(2015/01/08)
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- Liquid phase oxidation of n-octane to C8 oxygenates over modified Fe-MOF-5 catalysts
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The Metal Organic Framework materials Fe4-MOF-5, Fe 2-Zn2-MOF-5 and Fe0.9-Zn3. 1-MOF-5 were prepared. The XRD results showed the expected pattern of MOF-5 with a very sharp peak at a 2θ value below 10° which indicate that the material is highly crystalline. The SEM and TEM images showed that the catalysts are cubic in shape. The synthesised Fe4-MOF-5, Fe 2-Zn2-MOF-5 and Fe0.9-Zn3. 1-MOF-5 were tested in the oxidation of n-octane using H 2O2 as an oxidant in acetonitrile as solvent. Conversions of 10.5, 4.2 and 3.6% were obtained for Fe4-MOF-5, Fe 2-Zn2-MOF-5 and Fe0.9-Zn3. 1-MOF-5 respectively. It was observed that primary carbon activation increased with decreasing Fe content, as C-1 selectivities of 9.5, 12.9 and 19.8% were achieved for Fe4-MOF-5, Fe2-Zn 2-MOF-5 and Fe0.9-Zn3.1-MOF-5 respectively. Only C8 oxygenate products were observed, which include 1-octanol, 2-octanol, 3-octanol, 4-octanol, octanal, 2-octanone, 3-octanone, 4-octanone and octanoic acid. Furthermore, these catalysts were tested in the oxidation of cyclohexane using H2O2 in acetonitrile. Selectivities of 48.3% for cyclohexanol, 47.1% for cyclohexanone and 4.6% for hydroperoxycyclohexane were recorded at a conversion of 40% using Fe 4-MOF-5 as a catalyst.
- Cele, Mduduzi N.,Friedrich, Holger B.,Bala, Muhammad D.
-
-
- Liquid phase oxidation of n-octane to C8 oxygenates over modified Fe-MOF-5 catalysts
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The Metal Organic Framework materials Fe4-MOF-5, Fe2-Zn2-MOF-5 and Fe0.9-Zn3.1-MOF-5 were prepared. The XRD results showed the expected pattern of MOF-5 with a very sharp peak at a 2θ value below 10° which indicate that the material is highly crystalline. The SEM and TEM images showed that the catalysts are cubic in shape. The synthesised Fe4-MOF-5, Fe2-Zn2-MOF-5 and Fe0.9-Zn3.1-MOF-5 were tested in the oxidation of n-octane using H2O2as an oxidant in acetonitrile as solvent. Conversions of 10.5, 4.2 and 3.6% were obtained for Fe4-MOF-5, Fe2-Zn2-MOF-5 and Fe0.9-Zn3.1-MOF-5 respectively. It was observed that primary carbon activation increased with decreasing Fe content, as C-1 selectivities of 9.5, 12.9 and 19.8% were achieved for Fe4-MOF-5, Fe2-Zn2-MOF-5 and Fe0.9-Zn3.1-MOF-5 respectively. Only C8 oxygenate products were observed, which include 1-octanol, 2-octanol, 3-octanol, 4-octanol, octanal, 2-octanone, 3-octanone, 4-octanone and octanoic acid. Furthermore, these catalysts were tested in the oxidation of cyclohexane using H2O2in acetonitrile. Selectivities of 48.3% for cyclohexanol, 47.1% for cyclohexanone and 4.6% for hydroperoxycyclohexane were recorded at a conversion of 40% using Fe4-MOF-5 as a catalyst.
- Cele, Mduduzi N.,Friedrich, Holger B.,Bala, Muhammad D.
-
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- Highly atom-efficient and chemoselective reduction of ketones in the presence of aldehydes using heterogeneous catalysts
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The first demonstration of a 100% atom-efficient selective reduction of less reactive ketones over aldehydes using heterogeneous catalysts is reported. Extremely high selectivities for intra- and intermolecular reductions of ketones over aldehydes were achieved. This system was also applicable to a column reactor, leading to a gram-scale synthesis.
- Takahashi, Yusuke,Mitsudome, Takato,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
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supporting information
p. 2695 - 2698
(2013/10/08)
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- Highly selective bis(imino)pyridine iron-catalyzed alkene hydroboration
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Bis(imino)pyridine iron dinitrogen complexes have been shown to promote the anti-Markovnikov catalytic hydroboration of terminal, internal, and geminal alkenes with high activity and selectivity. The isolated iron dinitrogen compounds offer distinct advan
- Obligacion, Jennifer V.,Chirik, Paul J.
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supporting information
p. 2680 - 2683
(2013/07/19)
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- Borenium ion catalyzed hydroboration of alkenes with N-heterocyclic carbene-boranes
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Treatment of alkenes such as 3-hexene, 3-octene, and 1-cyclohexyl-1-butene with the N-heterocyclic carbene (NHC)-derived borane 2 and catalytic HNTf 2 (Tf = trifluoromethanesulfonyl (CF3SO2)) effects hydroboration at room temperature. With 3-hexene, surprisingly facile migration of the boron atom from C(3) of the hexyl group to C(2) was observed over a time scale of minutes to hours. Oxidative workup gave a mixture of alcohols containing 2-hexanol as the major product. A similar preference for the C(2) alcohol was observed after oxidative workup of the 3-octene and 1-cyclohexyl-1-butene hydroborations. NHC-borenium cations (or functional equivalents) are postulated as the species that accomplish the hydroborations, and the C(2) selective migrations are attributed to the four-center interconversion of borenium cations with cationic NHC-borane-olefin π-complexes.
- Prokofjevs, Aleksandrs,Boussonniere, Anne,Li, Linfeng,Bonin, Helene,Lacote, Emmanuel,Curran, Dennis P.,Vedejs, Edwin
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supporting information; experimental part
p. 12281 - 12288
(2012/09/22)
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- A heterogenized vanadium oxo-aroylhydrazone catalyst for efficient and selective oxidation of hydrocarbons with hydrogen peroxide
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A hydrazone Schiff base ligand derived from salicylaldehyde and benzhydrazide has been synthesized and reacted with vanadium(IV) leading to the corresponding vanadium(V) complex. The complex has been anchored on the surface of functionalized silica gel by N,O-coordination to the covalently Si-O bound modified salicylaldiminato ligand. The supported complex has been evaluated as a catalyst for hydrocarbon oxidation with hydrogen peroxide in acetonitrile. The heterogeneous system proved to be an efficient catalyst and was able to activate hydrogen peroxide toward the oxidation of alkenes, alkanes, benzene, and alkylaromatic compounds with more than 2,500 h-1 activity. Springer Science+Business Media B.V. 2011.
- Monfared, Hassan Hosseini,Abbasi, Vahideh,Rezaei, Adineh,Ghorbanloo, Massomeh,Aghaei, Alireza
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experimental part
p. 85 - 92
(2012/08/28)
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- Tuning the regio- and stereoselectivity of C-H activation in n-octanes by cytochrome P450 BM-3 with fluorine substituents: Evidence for interactions between a C-F bond and aromatic π systems
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We employed the water- soluble cytochrome P450 BM-3 to study the activity and regiospecificity of oxidation of fluorinated n-octanes. Three mutations, A74G, F87V, and L188Q, were introduced into P450 BM-3 to allow the system to undergo n-octane oxidation. In addition, the alanine at residue 328 was replaced with a phenylalanine to introduce an aromatic residue into the hydrophobic pocket to examine whether or not van der Waals interactions between a C-F substituent in the substrate and the polarizable π system of the phenylalanine may be used to steer the positioning of the substrate within the active-site pocket of the enzyme and control the regioselectivity and stereoselectivity of hydroxylation. Interestingly, not only was the regioselectivity controlled when the fluorine substituent was judiciously positioned in the substrate, but the electron input into the iron-heme group became tightly coupled to the formation of product, essentially without abortive side reactions. Remarkable enhancement of the coupling efficiency between electron input and product formation was observed for a range of fluorinated octanes in the enzyme even without the A328F mutation, presumably because of interactions of the C-F substituent with the π system of the porphyrin macrocycle within the active-site pocket. Evidently, tightening the protein domain containing the heme pocket tunes the distribution of accessible enzyme conformations and the associated protein dynamics that activate the iron porphyrin for substrate hydroxylation to allow the reactions mediated by the high-valent FeIV=O to become kinetically more commensurate with electron transfer from the flavin adenine dinucleotide (FAD)/flavin mononucleotide (FMN) reductase. These observations lend compelling evidence to support significant van der Waals interactions between the CF2 group and aromatic π systems within the heme pocket when the fluorinated octane substrate is bound. Activation of F-octanes: Cytochrome P450 BM-3-A74GF87VL188Q (see figure) and the A328F variant regionselectively converted fluorinated C8 alkanes to the corresponding secondary alcohols. The pattern of reactivity, especially the unprecedented regio- and stereoselectivity, observed for 4,4-difluorooctane suggested that specific interactions of the fluorinated substituent with aromatic π systems within the active site could tune the reactivity. Copyright
- Wu, Li-Lan,Yang, Chung-Ling,Lo, Feng-Chun,Chiang, Chih-Hsiang,Chang, Chun-Wei,Ng, Kok Yaoh,Chou, Ho-Hsuan,Hung, Huei-Ying,Chan, Sunney I.,Yu, Steve S.-F.
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experimental part
p. 4774 - 4787
(2011/11/14)
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- Screening of a minimal enriched P450 BM3 mutant library for hydroxylation of cyclic and acyclic alkanes
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A minimal enriched P450 BM3 library was screened for the ability to oxidize inert cyclic and acyclic alkanes. The F87A/A328V mutant was found to effectively hydroxylate cyclooctane, cyclodecane and cyclododecane. F87V/A328F with high activity towards cyclooctane hydroxylated acyclic n-octane to 2-(R)-octanol (46% ee) with high regioselectivity (92%).
- Weber, Evelyne,Seifert, Alexander,Antonovici, Mihaela,Geinitz, Christopher,Pleiss, Juergen,Urlacher, Vlada B.
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body text
p. 944 - 946
(2011/02/25)
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- Tuning a P450 enzyme for methane oxidation
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A new spin: The addition of chemically inert perfluoro carboxylic acids (green; see picture) to P450 enzymes results in dramatic activation of their catalytic activity as a result of the conversion of the Fe/heme from a low-spin to a high-spin state, and the reduction of the binding-pocket size. Together these effects allow otherwise inert substrates such as propane and even methane to be oxidized. Copyright
- Zilly, Felipe E.,Acevedo, Juan P.,Augustyniak, Wojciech,Deege, Alfred,Reetz, Manfred T.
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supporting information; experimental part
p. 2720 - 2724
(2011/06/10)
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- Mild homogeneous oxidation of alkanes and alcohols including glycerol with tert-butyl hydroperoxide catalyzed by a tetracopper(II) complex
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The homogeneous catalytic system composed of the aqua-soluble tetracopper(II) triethanolaminate complex [O?Cu4{N(CH2CH2O)3}4(BOH)4][BF4]2 (1), t-BuOOH (TBHP), water and acetonitrile solvent (optional) has been applied for the mild oxidation of (i) linear and cyclic alkanes to the corresponding alkyl peroxides, alcohols and ketones, (ii) secondary or primary alcohols to ketones or aldehydes, respectively and (iii) glycerol (GLY) to dihydroxyacetone (DHA). Unusual regio-, bond and stereoselectivity parameters have been determined for the alkane oxygenations and discussed in terms of possible steric, hydrophobic and electronic effects. In alcohol oxidations, secondary alcohols are the most reactive substrates. Yields and TONs up to 82% and 1200, respectively, have been obtained in the oxidation of isopropanol to acetone. The selective oxidation of GLY to DHA by the 1/TBHP system has been also achieved, although providing lower conversions. The 1/H2O2 system for the GLY oxidation is particularly advantageous in terms of selectivity and oxidant efficiency. These systems constitute one of the first examples of a metal-catalyzed oxidation of glycerol under homogeneous conditions.
- Kirillova, Marina V.,Kirillov, Alexander M.,Mandelli, Dalmo,Carvalho, Wagner A.,Pombeiro, Armando J.L.,Shul'Pin, Georgiy B.
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scheme or table
p. 9 - 17
(2010/09/09)
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- Immobilization of P450 BM-3 monooxygenase on mesoporous molecular sieves with different pore diameters
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The immobilization of the isolated heme domain of P450 BM-3 (BM3H_F87A) on two mesoporous molecular sieves, MCM-41 (pore diameter 25. A) and SBA-15 (pore diameter 60. A and 133. A) was examined systematically, and the activity of the immobilized enzyme toward para-nitrophenoxydodecanoic acid (12-pNCA) and n-octane was determined. Hydrogen peroxide was utilized as source of electrons and oxygen to support the monooxygenase activity of BM3H_F87A. The mesoporous materials were characterized by X-ray diffraction and nitrogen adsorption analyses before and after immobilization. The results revealed that the immobilization efficiency of MCM-41 and SBA-15 after single immersion was strongly affected by the pH value of the enzyme solution, initial enzyme concentration and agitation conditions. By modelling the 3D structure in silico and performing electrostatic potential calculations, the pH-dependence of the enzyme immobilization could be explained and a possible orientation of the protein on mesoporous materials was predicted. The oxidizing activity of the immobilized enzyme was found to depend on pore diameter and accessibility of the substrate for the enzyme. The highest activity toward 12-pNCA of 830. nmol product/mg P450/min was observed with BM3H_F87A immobilized on SBA-15 with pore diameter 133. A. Enzyme activity toward n-octane was similar for the enzyme immobilized on SBA-15 of 60. A and 133. A, and was at least two-fold higher as compared to a system with free enzyme.
- Weber, Evelyne,Sirim, Demet,Schreiber, Tino,Thomas, Bejoy,Pleiss, Juergen,Hunger, Michael,Glaeser, Roger,Urlacher, Vlada B.
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experimental part
p. 29 - 37
(2010/11/02)
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- Alkane oxidation by the H2O2-NaVO3-H2SO4 system in acetonitrile and water
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A simple system is described, which oxidizes saturated hydrocarbons either in acetonitrile or (less efficiently) in water. The system consists of 50% aqueous hydrogen peroxide as an oxidant, sodium metavanadate, NaVO3, as a catalyst and sulfuric (or oxalic) acid as a co-catalyst. The reactions were carried out at 20-50 °C. In the oxidation of cyclohexane in acetonitrile, the highest yield (37% based on cyclohexane) and turnover number (TON=1700) were attained after 3 h at 50 °C. The corresponding parameters were 16% and 1090 for n-heptane oxidation under the same conditions. The oxidation of higher alkanes, RH, in acetonitrile gives almost exclusively the corresponding alkyl hydroperoxides, ROOH. Light alkanes (n-butane, propane, ethane, and methane) have been also oxygenated by the system under consideration. The highest TON (200) was attained for ethane and the highest yield (19%) was obtained in the case of n-butane. The selectivity parameters measured for the oxidation of linear and branched alkanes are low, the reaction with cis- and trans-1,2-dimethylcyclohexanes is not stereoselective. These facts lead us to conclude that the oxidation occurs with the formation of hydroxyl radicals in the crucial step.
- Shul'pina, Lidia S.,Kirillova, Marina V.,Pombeiro, Armando J.L.,Shul'pin, Georgiy B.
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experimental part
p. 2424 - 2429
(2009/07/25)
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- Alkane oxidation by the system 'tert-butyl hydroperoxide-[Mn 2L2O3][PF6]2 (L = 1,4,7trimethyl-1,4,7-triazacyclononane)-carboxylic acid'
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The kinetics of cyclohexane (CyH) oxygenation with terf-butyl hydroperoxide (TBHP) in acetonitrile at 50°C catalysed by a dinuclear manganese(IV) complex 1 containing 1,4,7-trimethyl-1,4,7-triazacyclononane and co-catalysed by oxalic acid have been studied. It has been shown that an active form of the catalyst (mixed-valent dimeric species 'MnIIIMnIV,) is generated only in the interaction between complex 1 and TBHP and oxalic acid in the presence of water. The formation of this active form is assumed to be due to the hydrolysis of the Mn - O - Mn bonds in starting compound 1 and reduction of one MnIV to MnIII. A species which induces the CyH oxidation is radical tert-BuO generated by the decomposition of a monoperoxo derivative of the active form. The constants of the equilibrium formation and the decomposition of the intermediate adduct between TBHP and 1 have been measured: k = 7.4mol-1dm3 and k = 8.4 × 10 -2s-1, respectively, at [H2O] = 1.5 mol dm -3 and [oxalic acid] = 10-2 mol dm-3. The constant ratio for reactions of the monomolecular decomposition of tert-butoxy radical (tert-BuO → CH3COCH3+ CH3) and its interaction with the CyH (terf-BuO + CyH → fert-BuOH + Cy) was calculated: 0.26 mol dm-3. One of the reasons why oxalic acid accelerates the oxidation is due to the formation of an adduct between oxalic acid and 1 (K ≈ 103 mol-1 dm3). Copyright
- Kozlov, Yuriy N.,Nizova, Galina V.,Shul'pin, Georgiy B.
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p. 119 - 126
(2008/09/20)
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- Hydroperoxidation of alkanes with hydrogen peroxide catalyzed by aluminium nitrate in acetonitrile
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The first example of alkane oxygenation with hydrogen peroxide catalyzed by a non-transition metal derivative (aluminium) is reported. Heating (70 °C) a solution of an alkane, RH, hydrogen peroxide (70% aqueous) and a catalytic amount of Al(NO3)3·9H2O in air for a few hours afforded the corresponding alkyl hydroperoxide, ROOH. With cyclooctane, the hydroperoxide yield attained 31% and the maximum turnover number was 150. It is proposed on the basis of measurements of the selectivity parameters for the oxidation of linear and branched alkanes and a kinetic study that the oxidation occurs with the participation of hydroxyl radicals.
- Mandelli, Dalmo,Chiacchio, Karyna C.,Kozlov, Yuriy N.,Shul'pin, Georgiy B.
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scheme or table
p. 6693 - 6697
(2009/04/07)
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- Evolved CYP102A1 (P450BM3) variants oxidise a range of non-natural substrates and offer new selectivity options
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The evolution of CYP102A1 variants with enhanced activity and altered specificity characteristics. The Royal Society of Chemistry.
- Whitehouse, Christopher J. C.,Bell, Stephen G.,Tufton, Henry G.,Kenny, Richard J. P.,Ogilvie, Lydia C. I.,Wong, Luet-Lok
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p. 966 - 968
(2008/09/21)
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- Engineering cytochrome P450 BM3 for terminal alkane hydroxylation
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Enzymes that catalyze the terminal hydroxylation of alkanes could be used to produce more valuable chemicals from hydrocarbons. Cytochrome P450 BM3 from Bacillus megaterium hydroxylates medium-chain fatty acids at subterminal positions at high rates. To engineer BM3 for terminal alkane hydroxylation, we performed saturation mutagenesis at selected active-site residues of a BM3 variant that hydroxylates alkanes. Recombination of beneficial mutations generated a library of BM3 mutants that hydroxylate linear alkanes with a wide range of regioselectivities. Mutant 77-9H exhibits 52% selectivity for the terminal position of octane. This regioselectivity is octane-specific and does not transfer to other substrates, including shorter and longer hydrocarbons or fatty acids. These results show that BM3 can be readily molded for regioselective oxidation.
- Meinhold, Peter,Peters, Matthew W.,Hartwick, Adam,Hernandez, Alisha R.,Arnold, Frances H.
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p. 763 - 772
(2007/10/03)
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- Catalytic hydroxylation in biphasic systems using CYP102A1 mutants
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Cytochrome P450 monooxygenases are biocatalysts that hydroxylate or epoxidise a wide range of hydrophobic organic substrates. Their technical application is, however, limited to a small number of whole-cell processes. The use of the isolated P450 enzymes is believed to be impractical due to their low stability, stoichiometric need of the expensive cofactor NAD(P)H and low solubility of most substrates in aqueous media. We investigated the behaviour of an isolated bacterial monooxygenase (mutants of CYP102A1) in a biphasic reaction system supported by cofactor recycling with the NADP +-dependent formate dehydrogenase from Pseudomonas sp 101. Using this experimental set-up cyclohexane, octane and myristic acid were hydroxylated. To reduce the process costs a novel NADH-dependent mutant of CYP102A1 was designed. For recycling of NADH an NAD+-dependent FDH was used. The stability of the monooxygenase mutants under the reaction conditions in the biphasic system was quite high as revealed by total turnover numbers of up to 12,850 in the NADPH-dependent cyclohexane hydroxylation and up to 30,000 in the NADH-dependent myristic acid oxidation.
- Maurer, Steffen C.,Kuehnel, Katja,Kaysser, Leonard A.,Eiben, Sabine,Schmid, Rolf D.,Urlacher, Vlada B.
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p. 1090 - 1098
(2007/10/03)
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- Dod-S-Me and methyl 6-morpholinohexyl sulfide (MMS) as new odorless borane carriers
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Odorless Dod-S-Me (1) and MMS (3) are developed as efficient borane carriers. The yields of hydroborations and reductions with borane complex 2 of 1 are very high and the recovery of 1 after the reaction is quantitative. The borane complexes 4 and 5 of 3 are also useful. In the latter case chromatographic separation is unnecessary when excess oxidizing agent (alkaline H2O2) is used after hydroboration.
- Patra, Pranab K.,Nishide, Kiyoharu,Fuji, Kaoru,Node, Manabu
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p. 1003 - 1006
(2007/10/03)
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- Immobilisation of P450 BM-3 and an NADP+ Cofactor Recycling System: Towards a Technical Application of Heme-Containing Monooxygenases in Fine Chemical Synthesis
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Cytochrome P450 monooxygenases are potentially a very useful class of hydroxylation catalysts; they are able to introduce oxygen at activated and non-activated carbon-hydrogen bonds and thus lead to regio- and/or stereochemically pure compounds. However, this potential is lowered by their intrinsic low activity and inherent instability. P450-catalysed biotransformations require a constant supply of NAD(P)H, making the process an expensive one. To render these catalysts more suitable for industrial biocatalysis, the immobilisation of P450 BM-3 (CYP 102A1) from Bacillus megaterium in a sol-gel matrix was combined with a cofactor recycling system based on NADP+-dependent formate dehydrogenase (EC 1.2.1.2) from Pseudomonas sp. 101 and tested for practical applicability. This approach was used for the conversion of β-ionone, octane and naphthalene to the respective hydroxy compounds with DMSO as cosolvent using sol-gel immobilised P450 BM-3 mutants.
- Maurer, Steffen C.,Schulze, Holger,Schmid, Rolf D.,Urlacher, Vlada
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p. 802 - 810
(2007/10/03)
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- Hydrogen hydroperoxide oxidation of ethane and other alkanes catalyzed by chromium compounds
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Chromium oxo derivatives (H2CrO4) catalyze the effective oxidation of ethane and other saturated hydrocarbons with hydrogen peroxide or tert-butyl hydroperoxide in an acetonitrile solution at 60°C. Alkyl hydroperoxides, ketones (aldehydes), and alcohols are formed as main products. The oxidation of ethane gives ethyl hydroperoxide, acetaldehyde, ethanol, and acetic acid. The turnover frequency reaches 620 h-1 in this case, and the product yield in terms of H2O2 consumed is 21%.
- Suess-Fink,Shul'Pin
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- Transition-metal-promoted hydroboration of alkenes: A unique reversal of regioselectivity
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When hydroboration of 1-octene is carried out in the presence of catalytic amounts of rhodium trichloride followed by the usual oxidation (hydrogen peroxide in aqueous alkali), only minor proportions of 1-octanol (2.4%) are formed accompanied by very significant amounts of 2- (17.4%), 3- (36.9%), and 4-octanol (43.3%). These product compositions are obtained in good overall yield when the borane-THF complex is slowly added to a stirred solution of 1-octene in THF solvent containing the rhodium trichloride. Isomerization of 1-octene to 2-, 3-, and 4-octene in the presence of rhodium trichloride alone is far too slow to account for the foregoing results. The mechanism likely involves multiple and reversible addition/elimination of a Rh-activated B-H species across the double bonds.
- Morrill, Terence C.,D'Souza, Christopher A.,Yang, Lu,Sampognaro, Anthony J.
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p. 2481 - 2484
(2007/10/03)
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