- Access to Unsymmetrically Substituted Diaryl Gold N-Acyclic Carbene (NAC) and N-Heterocyclic Carbene (NHC) Complexes via the Isonitrile Route
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A variety of unsymmetric diaryl gold N-acyclic carbene (NAC) complexes was synthesized via the isonitrile route by three different methods: (a) solvent free in a melt, (b) mechanochemically and (c) in THF at room temperature. The latter method can also be used to synthesize unsaturated gold NHC complexes. These methods overall offer access to a broad array of new complexes and remove one of the previous limitations of the isonitrile route to NAC and NHC complexes of gold, namely the inability to react with the less nucleophilic aromatic amines. The new complexes also proved to be successful as pre-catalysts in the gold-catalyzed phenol synthesis. (Figure presented.).
- Vethacke, Vanessa,Claus, Vanessa,Dietl, Martin C.,Ehjeij, Daniel,Meister, Arne,Huber, Jonas F.,Paschai Darian, Leon K.,Rudolph, Matthias,Rominger, Frank,Hashmi, A. Stephen K.
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supporting information
p. 536 - 554
(2021/10/20)
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- Tetracoordinate borates as catalysts for reductive formylation of amines with carbon dioxide
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We report sodium trihydroxyaryl borates as the first robust tetracoordinate organoboron catalysts for reductive functionalization of CO2. These catalysts, easily synthesized from condensing boronic acids with metal hydroxides, activate main group element-hydrogen (E-H) bonds efficiently. In contrast to BX3 type boranes, boronic acids and metal-BAr4 salts, under transition metal-free conditions, sodium trihydroxyaryl borates exhibit high reactivity of reductive N-formylation toward a variety of amines (106 examples), including those with functional groups such as ester, olefin, hydroxyl, cyano, nitro, halogen, MeS-, ether groups, etc. The over-performance to catalyze formylation of challenging pyridyl amines affords a promising alternative method to the use of traditional formylation reagents. Mechanistic investigation supports electrostatic interactions as the key for Si/B-H activation, enabling alkali metal borates as versatile catalysts for hydroborylation, hydrosilylation, and reductive formylation/methylation of CO2.
- Du, Chen-Xia,Huang, Zijun,Jiang, Xiaolin,Li, Yuehui,Makha, Mohamed,Wang, Fang,Zhao, Dongmei
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supporting information
p. 5317 - 5324
(2020/09/17)
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- A NHC-silyliumylidene cation for catalytic N?formylation of amines using carbon dioxide
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This study describes the use of a silicon(II) complex, namely, the NHC-silyliumylidene cation complex [(IMe)2SiH]I (1, IMe =:C{N(Me)C(Me)}2), to catalyze the chemoselective N-formylation of primary and secondary amines using CO2 and PhSiH3 under mild conditions to afford the corresponding formamides as a sole product (average reaction time: 4.5 h; primary amines, average yield: 95%, average TOF: 8 h?1; secondary amines, average yield: 98%, average TOF: 17 h?1). The activity of 1 and product yields outperform the currently available non-transition-metal catalysts used for this catalysis. Mechanistic studies show that the silicon(II) center in complex 1 catalyzes the C?N bond formation via a different pathway in comparison with non-transition-metal catalysts. It sequentially activates CO2, PhSiH3, and amines, which proceeds via a dihydrogen elimination mechanism, to form formamides, siloxanes, and dihydrogen gas.
- Leong, Bi-Xiang,Teo, Yeow-Chuan,Condamines, Cloe,Yang, Ming-Chung,Su, Ming-Der,So, Cheuk-Wai
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p. 14824 - 14833
(2020/12/21)
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- Photophysical processes in rhenium(I) diiminetricarbonyl arylisocyanides featuring three interacting triplet excited states
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We present a series of four transition-metal complexes based on the rhenium(I) tricarbonyl 1,10-phenanthroline (phen) template, with a lone ancillary arylisocyanide (CNAr) ligand to yield metal-organic chromophores of the generic molecular formula [Re(phen)-(CO)3(CNAr)]+ [CNAr = 2,6-diisopropylphenyl isocyanide (1), 4-phenyl-2,6-diisopropylphenyl isocyanide (2), 4-phenylethynyl-2,6-diisopropylphenyl isocyanide (3), and 4-biphenyl-2,6-diisopropylphenyl isocyanide (4)]. This particular series features varied degrees of π-conjugation length in the CNAr moiety, resulting in significant modulation in the resultant photophysical properties. All molecules possess long-lived [8- 700 μs at room temperature (RT)], strongly blue-green photoluminescent and highly energetic excited states λmax,em = 500-518 nm; Φ = 14-64%). Each of these chromophores has been photophysically investigated using static and dynamic spectroscopic techniques, the latter probed from ultrafast to suprananosecond time scales using transient absorption and photoluminescence (PL). Time-resolved PL intensity decays recorded as a function of the temperature were consistent with the presence of at least two emissive states lying closely spaced in energy with a third nonemissive state lying much higher in energy and likely ligand-field in character. The combined experimental evidence, along with the aid of electronic structure calculations (density functional theory and time-dependent density functional theory performed at the M06/Def2-SVP/SDD level), illustrates that the CNAr ligand is actively engaged in manipulating the excited-state decay in three of these molecules (2-4), wherein the triplet metal-to-ligand charge-transfer (3MLCT) state along with two distinct triplet ligand-centered (3LC) excited-state configurations (phen and CNAr) conspire to produce the resultant photophysical properties. Because the π conjugation within the CNAr ligand was extended, an interesting shift in the dominant photophysical processes was observed. When the CNAr conjugation length is short, as in 1, the phenanthroline 3LC state dominates, resulting in a configurationally mixed triplet excited state of both LC and MLCT character. With more extended π conjugation in the CNAr subunit (2-4), the initially generated 3LC(phen)/3MLCT excited state ultimately migrates to the CNAr 3LC state on the order of tens of picoseconds. Molecules 3 and 4 in this series also feature unique examples of inorganic excimer formation, as evidenced by dynamic self-quenching in the corresponding PL intensity decays accompanied by the observation of a short-lived low-energy emission feature.
- Favale, Joseph M.,Danilov, Evgeny O.,Yarnell, James E.,Castellano, Felix N.
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supporting information
p. 8750 - 8762
(2019/08/20)
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- Palladium-Catalyzed Diarylation of Isocyanides with Tetraarylleads for the Selective Synthesis of Imines and α-Diimines
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Using tetraaryllead compounds (PbAr4) as arylating reagents, isocyanides undergo selective diarylation in the presence of palladium catalysts such as Pd(OAc)2 or Pd(PPh3)4 to afford imines and/or α-diimines based on the isocyanide employed. With aliphatic isocyanides, imines are obtained preferentially, whereas α-diimines are formed in the case of electron-rich aromatic isocyanides. The differences in imine/α-diimine selectivity can be attributed to the stability of imidoylpalladium intermediates formed in this catalytic reaction. Compared with other arylating reagents, tetraaryllead compounds are excellent candidates for use in the selective transformations to imines and/or α-diimines, especially in terms of inhibiting the oligomerization of isocyanides, which results in a lower product selectivity in many transition-metal-catalyzed reactions of isocyanides.
- Tran, Cong Chi,Kawaguchi, Shin-Ichi,Kobiki, Yohsuke,Matsubara, Hitomi,Tran, Dat Phuc,Kodama, Shintaro,Nomoto, Akihiro,Ogawa, Akiya
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p. 11741 - 11751
(2019/10/02)
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- Diverse catalytic reactivity of a dearomatized PN3P?-nickel hydride pincer complex towards CO2 reduction
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A dearomatized PN3P?-nickel hydride complex has been prepared using an oxidative addition process. The first nickel-catalyzed hydrosilylation of CO2 to methanol has been achieved, with unprecedented turnover numbers. Selective methylation and formylation of amines with CO2 were demonstrated by such a PN3P?-nickel hydride complex, highlighting its versatile functions in CO2 reduction.
- Li, Huaifeng,Gon?alves, Théo P.,Zhao, Qianyi,Gong, Dirong,Lai, Zhiping,Wang, Zhixiang,Zheng, Junrong,Huang, Kuo-Wei
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supporting information
p. 11395 - 11398
(2018/10/20)
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- Porous Organic Polymers with Built-in N-Heterocyclic Carbenes: Selective and Efficient Heterogeneous Catalyst for the Reductive N-Formylation of Amines with CO2
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A series of porous organic polymers (POPs) based on N-heterocyclic carbene (NHC) building blocks has been prepared through an octacarbonyldicobalt complex [Co2(CO)8]-catalyzed trimerization of terminal alkyne groups. By changing the monomer ratio in the copolymerization, cross-linked POPs with tunable surface areas of 485–731 m2 g?1 and pore volumes of 0.31–0.51 cm3 g?1 were easily prepared. Compared with the analogues homogeneous NHC (SIPr) catalysts, the POPs exhibited an enhanced catalytic activity and high selectivity in the reductive functionalization of CO2 with amines. The extraordinary performance of the sample could be attributed to the combination of the gas enrichment (or storage) effect, enhanced in-pore concentrations of other substrates, and advantageous micropore structures of the porous polymers. Meanwhile, these catalysts can easily be separated and recycled from the reaction systems with only a slight loss of activity. This excellent catalytic performance and facile recycling of heterogeneous catalysts make them very attractive. These NHC-containing POPs may provide a new platform for catalytic transformations of CO2.
- Lv, Hui,Wang, Wenlong,Li, Fuwei
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p. 16588 - 16594
(2018/10/24)
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- Synthesis and structure elucidation of allyl Pd(II) complexes of NHC ligands derived from substituted imidazo[1,5-a]quinolin-1(2H)-ylidene
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Nine Pd(II) complexes involving N-heterocyclic carbenes (NHCs) derived from 2-substituted and 2- and 7-substituted imidazo[1,5-a]quinolin-1(2H)-ylidene with auxiliary allylic ligands were synthesized and characterized. The structure and configuration of the complexes were elucidated on the basis of combination of dynamic NMR and DFT studies. Conformational studies in respect of hindered rotation around Pd-C bond and η3-η1-η3 pseudo allyl rotation were performed. The results from dynamic NMR and DFT studies confirmed the mechanism of selective η3-η1-η3 isomerization, whose energy barriers are affected by steric hindrance of substituents at nitrogen atom. Energy barriers of isomerization (16.7–18.8 kcal/mol) are slightly influenced by the electronic nature of substituents at seventh position in imidazo[1,5-a]quinolin-1(2H)-ylidene moiety. The results from DFT calculations were in good agreement with the experimental energy barriers.
- Lyapchev, Rumen,Petrov, Petar,Dangalov, Miroslav,Vassilev, Nikolay G.
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p. 194 - 209
(2017/10/09)
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- Catalyst-free: N -formylation of amines using BH3NH3 and CO2 under mild conditions
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The catalyst-free N-formylation of amines using CO2 as the C1 source and BH3NH3 as the reductant has been developed for the first time. The corresponding formylated products of both primary and secondary amines are obtained in good to excellent yields (up to 96% of isolated yield) under mild conditions.
- Zhao, Tian-Xiang,Zhai, Gao-Wen,Liang, Jian,Li, Ping,Hu, Xing-Bang,Wu, You-Ting
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supporting information
p. 8046 - 8049
(2017/07/22)
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- Electrostatic Catalyst Generated from Diazadiborinine for Carbonyl Reduction
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Since the seminal discovery by van der Waals in the late 19th century that weak attractive forces exist between even electrically neutral atoms or molecules, a number of noncovalent interactions have been recognized. Among them, electrostatic interactions such as hydrogen bonds play pivotal roles in countless chemical processes and biochemical living systems. By mimicking biocatalysis, various organocatalysts equipped with hydrogen-bond functionality have been developed; however, a challenge has persisted in designing catalysts exploiting other types of noncovalent interactions. Here, we report metal-free hydroboration reactions of carbonyl compounds and CO2 catalyzed by aromatic diazadiborinine. A joint experimental and computational study on the reaction mechanism suggests that adducts of diazadiborinine with carbonyl and CO2 formed at the initial stage of the reactions serve as actual catalysts. The former stabilizes the transition state by using the electrostatic interaction between the hydride of borane and the polar, hole-shaped structure of the adduct.
- Wu, Di,Wang, Ruixing,Li, Yongxin,Ganguly, Rakesh,Hirao, Hajime,Kinjo, Rei
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supporting information
p. 134 - 151
(2017/07/17)
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- Chemoselective Schwartz Reagent Mediated Reduction of Isocyanates to Formamides
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Addition of the in situ generated Schwartz reagent to widely available isocyanates constitutes a chemoselective, high-yielding, and versatile approach to the synthesis of variously functionalized formamides. Steric and electronic factors or the presence of sensitive functionalities (esters, nitro groups, nitriles, alkenes) do not compromise the potential of the method. Full preservation of the stereochemical information contained in the starting materials is observed. The use of formamides in the nucleophilic addition of organometallic reagents (Chida-Sato allylation, Charette-Huang addition to imidoyl triflate activated amides, Matteson homologation of boronic esters) is briefly investigated.
- Pace, Vittorio,De La Vega-Hernández, Karen,Urban, Ernst,Langer, Thierry
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supporting information
p. 2750 - 2753
(2016/06/15)
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- Synthesis, characterization and catalytic activity of stable [(NHC)H][ZnXY2] (NHC?=?N-Heterocyclic carbene, X, Y?=?Cl, Br) species
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The synthesis and characterization of imidazol(in)ium-based zinc(II) halide salts are reported. These compounds present interesting structural features and exhibit high stability. Their catalytic activity was explored in the methylation of amines with CO2 and PhSiH3.
- Santoro, Orlando,Nahra, Fady,Cordes, David B.,Slawin, Alexandra M.Z.,Nolan, Steven P.,Cazin, Catherine S.J.
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- Biomass-derived γ-valerolactone as an efficient solvent and catalyst for the transformation of CO2 to formamides
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Efficient conversion of carbon dioxide (CO2) into valuable chemicals is a very attractive topic. Herein, we conducted the first work on the utilization of biomass-derived γ-valerolactone (GVL) as the solvent and catalyst for transformation of CO2 with various primary and secondary amines in the presence of phenylsilane (PhSiH3), and the corresponding desired formamides were produced with high yields without any additional catalyst. Systematic studies indicated that the lactone structure of GVL played a key role in the formation of the active silyl formates and the activation of N-H bonds in amines, thus leading to the excellent performance of GVL for the catalytic reactions.
- Song, Jinliang,Zhou, Baowen,Liu, Huizhen,Xie, Chao,Meng, Qinglei,Zhang, Zhanrong,Han, Buxing
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supporting information
p. 3956 - 3961
(2016/07/21)
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- Acyclic aminocarbene-like palladium complex-catalyzed Suzuki-Miyaura reaction at low catalyst loadings
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A series of air-stable aminocarbene-like palladium(II) complexes were easily prepared by the reaction of bis-aromaticisocyanide-dichloropalladium(II) with N-arylbenzamidines. 0.1 mol % of the optimal palladium complex 3a showed excellent catalytic activity for Suzuki-Miyaura cross-coupling reaction at room temperature and the desired products were isolated in up to 98% yields. Moreover, a large-scale reaction showed that 0.01 mol % 3a was enough to catalyze the coupling reaction efficiently at room temperature to give the desired product in 93% yield.
- Fang, Yi,Wang, Shun-Yi,Ji, Shun-Jun
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supporting information
p. 9679 - 9683
(2015/12/04)
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- Palladium-catalyzed direct coupling of 2-vinylanilines and isocyanides: An efficient synthesis of 2-aminoquinolines
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Palladium-catalyzed oxidative coupling of 2-vinylanilines and isocyanides constitutes a direct, facile, and efficient approach to 2-aminoquinolines. The procedure, employing palladium acetate and silver carbonate, is attractive in terms of assembly efficiency, functional group tolerance, and operational simplicity. A variety of 2-aminoquinolines were prepared in good to excellent yields.
- Wang, Lijie,Ferguson, Jamie,Zeng, Fanlong
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supporting information
p. 11486 - 11491
(2015/12/04)
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- N-heterocyclic carbene copper(i) catalysed N-methylation of amines using CO2
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The N-methylation of amines using CO2 and PhSiH3 as source of CH3 was efficiently performed using a N-heterocyclic carbene copper(i) complex. The methodology was found compatible with aromatic and aliphatic primary and secondary amines. Synthetic and computational studies have been carried out to support the proposed reaction mechanism for this transformation.
- Santoro, Orlando,Lazreg, Fama,Minenkov, Yury,Cavallo, Luigi,Cazin, Catherine S. J.
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p. 18138 - 18144
(2015/10/28)
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- Hydrophosphination of CO2 and Subsequent Formate Transfer in the 1,3,2-Diazaphospholene-Catalyzed N-Formylation of Amines
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Hydrophosphination of CO2 with 1,3,2-Diazaphospholene (NHP-H; 1) afforded phosphorus formate (NHP-OCOH; 2) through the formation of a bond between the electrophilic phosphorus atom in 1 and the oxygen atom from CO2, along with hydride transfer to the carbon atom of CO2. Transfer of the formate from 2 to Ph2SiH2 produced Ph2Si(OCHO)2 (3) in a reaction that could be carried out in a catalytic manner by using 5 mol % of 1. These elementary reactions were applied to the metal-free catalytic N-formylation of amine derivatives with CO2 in one pot under ambient conditions.
- Chong, Che Chang,Kinjo, Rei
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supporting information
p. 12116 - 12120
(2015/10/12)
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- From isonitriles to unsaturated NHC complexes of gold, palladium and platinum
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In a modular template synthesis, unsaturated NHC complexes of gold, palladium and platinum were synthesized from simple metal salts, isonitriles and amines with acetal or ketal groups. Upon the addition of amines with tethered acetal or ketal moieties to the metal-activated isonitrile, first nitrogen acyclic carbene (NAC) complexes are formed. These undergo ring closure and elimination to the unsaturated NHC complexes upon addition of acid. This simple strategy opens an attractive and fast approach to NHC complexes of gold, palladium and platinum. The modular approach allows a fast modification and is well-suited for the synthesis of unsymetrically and symmetrically substituted unsaturated NHC complexes.
- Riedel, Dominic,Wurm, Thomas,Graf, Katharina,Rudolph, Matthias,Rominger, Frank,Hashmi, A. Stephen K.
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supporting information
p. 1515 - 1523
(2015/05/19)
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- Method for Preparing Formamide Compounds
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The present invention relates to a method for preparing formamide compounds using carbon dioxide, and to the use of said method for manufacturing vitamins, pharmaceutical products, adhesives, acrylic fibres, synthetic leathers, pesticides and fertilisers. The invention also relates to a method for manufacturing vitamins, pharmaceutical products, adhesives, acrylic fibres, synthetic leathers, pesticides and fertilisers which includes a step of preparing formamide compounds by the method according to the invention.
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Paragraph 0126-0136
(2014/02/16)
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- Iron-catalyzed hydrosilylation of CO2: CO2 conversion to formamides and methylamines
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Catalytic hydrosilylation of CO2 is an efficient and selective approach to form chemicals. Herein, we describe the first iron catalysts able to promote the reductive functionalization of CO2 using hydrosilanes as reductants. Iron(ii) salts supported by phosphine donors enable the conversion of CO2 to formamide and methylamine derivatives under mild reaction conditions. This journal is the Partner Organisations 2014.
- Frogneux, Xavier,Jacquet, Olivier,Cantat, Thibault
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p. 1529 - 1533
(2014/06/09)
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- Generation of powerful tungsten reductants by visible light excitation
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The homoleptic arylisocyanide tungsten complexes, W(CNXy)6 and W(CNIph)6 (Xy = 2,6-dimethylphenyl, Iph = 2,6-diisopropylphenyl), display intense metal to ligand charge transfer (MLCT) absorptions in the visible region (400-550 nm). MLCT emission (λmax ≈ 580 nm) in tetrahydrofuran (THF) solution at rt is observed for W(CNXy)6 and W(CNIph)6 with lifetimes of 17 and 73 ns, respectively. Diffusion-controlled energy transfer from electronically excited W(CNIph) 6 (*W) to the lowest energy triplet excited state of anthracene (anth) is the dominant quenching pathway in THF solution. Introduction of tetrabutylammonium hexafluorophosphate, [Bun4N][PF 6], to the THF solution promotes formation of electron transfer (ET) quenching products, [W(CNIph)6]+ and [anth] ?-. ET from*W to benzophenone and cobalticenium also is observed in [Bun4N][PF6]/THF solutions. The estimated reduction potential for the [W(CNIph)6]+/ *W couple is -2.8 V vs Cp2Fe+/0, establishing W(CNIph)6 as one of the most powerful photoreductants that has been generated with visible light.
- Sattler, Wesley,Ener, Maraia E.,Blakemore, James D.,Rachford, Aaron A.,Labeaume, Paul J.,Thackeray, James W.,Cameron, James F.,Winkler, Jay R.,Gray, Harry B.
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supporting information
p. 10614 - 10617
(2013/08/23)
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- Recycling of carbon and silicon wastes: Room temperature formylation of N-H bonds using carbon dioxide and polymethylhydrosiloxane
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A highly active organocatalytic system based on N-heterocyclic carbenes has been designed for the formylation of N-H bonds in a large variety of nitrogen molecules and heterocycles, using two chemical wastes: CO2 and polymethylhydrosiloxane (PMHS).
- Jacquet, Olivier,Das Neves Gomes, Christophe,Ephritikhine, Michel,Cantat, Thibault
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supporting information; experimental part
p. 2934 - 2937
(2012/03/27)
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- N-Heterocyclic Carbene Complexes, Their Preparation And Use
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Described are N-heterocyclic carbene complexes of the formula I, where n is 0 or 1, M is a metal atom containing group, R1 is selected from hydrogen alkyl, cycloalkyl, heterocycloalkyl, aryl and hetaryl, R2 is selected from hydrogen, alkyl, cycloalkyl, heterocycloalkyl, aryl and hetaryl, wherein R1 and R2 do not both stand for hydrogen. Furthermore, also described are methods for their preparation and their use as catalysts employed in a C—C, C—O, C—N or C—H bond formation reaction.
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Page/Page column 25
(2012/05/07)
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- N-HETEROCYCLIC CARBENE COMPLEXES, THEIR PREPARATION AND USE
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N-heterocyclic carbene complexes of the formula (I) is disclosed, wherein the radicals have the meanings as defined in the invention. The preparation and the use as catalysts employed in a C-C, C-O, C-N or C-H bond formation reaction of said complexes are also disclosed.
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Page/Page column 63-64
(2012/05/19)
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- A short way to switchable carbenes
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A new, one-step route to N-heterocyclic oxo-carbene complexes (NHOCs), representatives of chemo-switchable NHC complexes, is reported. This simple procedure provides an easy access to gold, palladium and platinum complexes of these ligands. Copyright
- Hashmi, A. Stephen K.,Lothschuetz, Christian,Graf, Katharina,Haeffner, Tobias,Schuster, Andreas,Rominger, Frank
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supporting information; experimental part
p. 1407 - 1412
(2011/08/07)
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- Carbenes made easy: Formation of unsymmetrically substituted N-heterocyclic carbene complexes of palladium(II), platinum(II) and gold(I) from coordinated isonitriles and their catalytic activity
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From palladium(II) or platinum(II) bis(isonitrile) complexes and from gold(I) isonitrile complexes, both easily available from simple precursors, the corresponding mono-N-heterocyclic carbene (NHC) complexes could be obtained selectively in good yields under very mild conditions. The reagents are simple β-chloroammonium salts in the presence of a weak base. Unsymmetric NHC complexes are accessible. Thus over only two steps from simple metal precursors a broad variety of NHC complexes is available, the method is ideal to quickly assemble catalyst libraries. The palladium complexes are active pre-catalysts in Suzuki cross-coupling even with the additional isonitrile ligand on palladium. Copyright
- Hashmi, A. Stephen K.,Lothschuetz, Christian,Boehling, Constantin,Hengst, Tobias,Hubbert, Christoph,Rominger, Frank
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supporting information; experimental part
p. 3001 - 3012
(2011/03/20)
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- Synthesis and activity of ruthenium olefin metathesis catalysts coordinated with thiazol-2-ylidene ligands
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A new family of ruthenium-based olefin metathesis catalysts bearing a series of thiazole-2-ylidene ligands has been prepared. These complexes are readily accessible in one step from commercially available (PCy 3)2Cl2Ru=CHPh or (PCy3)Cl 2Ru=CH(o-iPrO-Ph) and have been fully characterized. The X-ray crystal structures of four of these complexes are disclosed. In the solid state, the aryl substituents of the thiazole-2-ylidene ligands are located above the empty coordination site of the ruthenium center. Despite the decreased steric bulk of their ligands, all of the complexes reported herein efficiently promote benchmark olefin metathesis reactions such as the ring-closing of diethyldiallyl and diethylallylmethallyl malonate and the ring-opening metathesis polymerization of 1,5-cyclooctadiene and norbornene, as well as the cross metathesis of allyl benzene with cis-1,4-diacetoxy-2-butene and the macrocyclic ring-closing of a 14-membered lactone. The phosphine-free catalysts of this family are more stable than their phosphine-containing counterparts, exhibiting pseudo-first-order kinetics in the ring-closing of diethyldiallyl malonate. Upon removing the steric bulk from the ortho positions of the N-aryl group of the thiazole-2-ylidene ligands, the phosphine-free catalysts lose stability, but when the substituents become too bulky the resulting catalysts show prolonged induction periods. Among five thiazole-2-ylidene ligands examined, 3-(2,4,6-trimethylphenyl)-and 3-(2,6-diethylphenyl)-4,5-dimethylthiazol-2- ylidene afforded the most efficient and stable catalysts. In the cross metathesis reaction of allyl benzene with cis-1,4-diacetoxy-2-butene increasing the steric bulk at the ortho positions of the N-aryl substituents results in catalysts that are more Z-selective.
- Vougioukalakis, Georgios C.,Grubbs, Robert H.
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p. 2234 - 2245
(2008/09/18)
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- Screw Sense Selective Polymerization of Achiral Isocyanides Catalysed by Optically Active Nickel(II) Complexes
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Poly(isocyanides), (RN=Cn, can be prepared from isocyanides, , by the catalytic action of nickel(II) compounds.The main chain of these polymers is a rigid helix.This helical conformation results from a restricted rotation around the single bonds that connect the main-chain carbon atoms.Polymerization of achiral isocyanides generally gives a racemic mixture of left- and right-handed helices, whereas polymerization of optically active isocyanides results in helices with an excess of one screw sense.We describe a procedure for obtaining poly(isocyanides) with predominantly one screw sense, starting from an achiral monomer.A catalyst is prepared by adding an optically active amine to a tetrakis(isocyanide)nickel(II) perchlorate complex.Polymerization of various achiral isocyanides with this catalist yields optically active polymers with an enantiomeric excess up to 83percent.
- Kamer, Paul C. J.,Nolte, Roeland J. M.,Drenth, Wiendelt
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p. 6818 - 6825
(2007/10/02)
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- A HIGHLY EFFICIENT AND GENERAL N-MONOMETHYLATION OF FUNCTIONALIZED PRIMARY AMINES VIA FORMYLATION -- BORANE:METHYL SULFIDE REDUCTION
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Formylation of functionalized primary aromatic and aliphatic amines with acetic formic anhydride (AFA) followed by borane:methyl sulfide reduction in the same pot affords the corresponding N-methylamines in excellent isolated yields, uncontaminated by bis alkylation; the reaction sequence is applicable to even very weakly basic and sterically hindered amines.
- Krishnamurthy, S.
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p. 3315 - 3318
(2007/10/02)
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