- Synthesis of mesoionic n-heterocyclic olefins and catalytic application for hydroboration reactions
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Mesoionic N-heterocyclic olefins have been developed, which feature high ylidic character. These compounds have been used as efficient catalysts for hydroboration of imines, nitriles, and N-heteroarenes.
- Yan, Xiaoyu,Zhang, Zengyu,Huang, Shiqing,Huang, Linwei,Xu, Xingyu,Zhao, Hongyan
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- Hydroboration of nitriles and imines by highly active zinc dihydride catalysts
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Eco-friendly zinc dihydrides stabilized by N-heterocyclic carbenes were demonstrated to be highly efficient catalysts for the double hydroboration of nitriles with pinacolborane, exhibiting turnover frequencies up to 3000 h-1 at room temperature under sol
- Wang, Xiaoming,Xu, Xin
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Read Online
- Hydroboration and reductive amination of ketones and aldehydes with HBpin by a bench stable Pd(ii)-catalyst
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A palladium(ii) complex [(κ4-{1,2-C6H4(NCH-C6H4O)2}Pd] (1) supported by a dianionic salen ligand [1,2-C6H4(NCH-C6H4O)2]2- (L) was synthesised and used as a molecular pre-catalyst in the hydroboration of aldehydes and ketones. The molecular structure of Pd(ii) complex 1 was established by single-crystal X-ray diffraction analysis. Complex 1 was tested as a competent pre-catalyst in the hydroboration of aldehydes and ketones with pinacolborane (HBpin) to produce corresponding boronate esters in excellent yields at ambient temperature under solvent-free conditions. Further, the complex 1 proved to be a competent catalyst in the reductive amination of aldehydes with HBpin and primary amines under mild and solvent-free conditions to afford a high yield (up to 97%) of corresponding secondary amines. Both protocols provided high conversion, superior selectivity and broad substrate scope, from electron-withdrawing to electron-donating and heterocyclic substitutions. A computational study based on density functional theory (DFT) revealed a reaction mechanism for Pd-catalysed hydroboration of carbonyl species in the presence of HBpin. The protocols also uncovered the dual role of HBpin in achieving the hydroboration reaction.
- Biswas, Bhaskar,Devadkar, Ajitrao Kisan,Gupta, Puneet,Joshi, Mayank,Mahato, Shreya,Panda, Tarun K.,Rawal, Parveen,Roy Choudhury, Angshuman
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supporting information
p. 1103 - 1111
(2022/02/11)
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- Catalytic Hydroboration and Reductive Amination of Carbonyl Compounds by HBpin using a Zinc Promoter
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The chemoselective hydroboration of aldehydes and ketones, catalyzed by Zinc(II) complexes [κ2-(PyCH=NR)ZnX2] [R=CPh3, X=Cl (1) and R=Dipp (2,6-diisoropylphenyl) and X=I (2)], in the presence of pinacolborane (HBpin) at ambient temperature and under solvent-free conditions, which produced the corresponding boronate esters in high yield, is reported. Zinc metal complexes 1 and 2 were derived in 80–90% yield from the reaction of iminopyridine [PyCH=NR] with anhydrous zinc dichloride in dichloromethane at room temperature. The solid-state structures of both zinc complexes were confirmed using X-ray crystallography. Zinc complex 1 was also used as a competent pre-catalyst in the reductive amination of carbonyl compounds with HBpin under mild and solvent-free conditions to afford a high yield (up to 97%) of the corresponding secondary amines. The wider substrate scope of both reactions was explored. Catalytic protocols using zinc as a pre-catalyst demonstrated an atom-economic and green method with diverse substrates bearing excellent functional group tolerance. Computational studies established a plausible mechanism for catalytic hydroboration.
- Kumar, Ravi,Rawal, Parveen,Banerjee, Indrani,Pada Nayek, Hari,Gupta, Puneet,Panda, Tarun K.
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supporting information
(2022/02/05)
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- Hydroborative reduction of amides to amines mediated by La(CH2C6H4NMe2-: O)3
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The deoxygenative reduction of amides to amines is a great challenge for resonance-stabilized carboxamide moieties, although this synthetic strategy is an attractive approach to access the corresponding amines. La(CH2C6H4NMe2-o)3, a simple and easily accessible lanthanide complex, was found to be highly efficient not only for secondary and tertiary amide reduction, but also for the most challenging primary reduction with pinacolborane. This protocol exhibited good tolerance for many functional groups and heteroatoms, and could be applied to gram-scale synthesis. The active species in this catalytic cycle was likely a lanthanide hydride.
- Gong, Mingliang,Guo, Chenjun,Luo, Yunjie,Xie, Hongzhen,Zhang, Fangcao
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p. 779 - 791
(2022/01/22)
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- Aza-Matteson Reactions via Controlled Mono-and Double-Methylene Insertions into Nitrogen-Boron Bonds
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Boron-homologation reactions represent an efficient and programmable approach to prepare alkylboronates, which are valuable and versatile synthetic intermediates. The typical boron-homologation reaction, also known as the Matteson reaction, involves formal carbenoid insertions into C-B bonds. Here we report the development of aza-Matteson reactions via carbenoid insertions into the N-B bonds of aminoboranes. By changing the leaving groups of the carbenoids and altering Lewis acid activators, selective mono- and double-methylene insertions can be realized to access various α- and β-boron-substituted tertiary amines, respectively, from common secondary amines. The derivatization of complex amine-containing bioactive molecules, diverse functionalization of the boronate products, and sequential insertions of different carbenoids have also been achieved.
- Xie, Qiqiang,Dong, Guangbin
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supporting information
p. 14422 - 14427
(2021/09/29)
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- Lithium compound catalyzed deoxygenative hydroboration of primary, secondary and tertiary amides
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A selective and efficient route for the deoxygenative reduction of primary to tertiary amides to corresponding amines has been achieved with pinacolborane (HBpin) using simple and readily accessible 2,6-di-tert-butyl phenolate lithium·THF (1a) as a catalyst. Both experimental and DFT studies provide mechanistic insight. This journal is
- Bisai, Milan Kumar,Gour, Kritika,Das, Tamal,Vanka, Kumar,Sen, Sakya S.
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supporting information
p. 2354 - 2358
(2021/03/03)
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- Reduction of Amides to Amines with Pinacolborane Catalyzed by Heterogeneous Lanthanum Catalyst La(CH2C6H4NMe2- o)3@SBA-15
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Hydroboration of amides is a useful synthetic strategy to access the corresponding amines. In this contribution, it was found that the supported lanthanum benzyl material La(CH2C6H4NMe2-o)3@SBA-15 was highly active for the hydroboration of primary, secondary, and tertiary amides to amines with pinacolborane. These reactions selectively produced target amines and showed good tolerance for functional groups such as -NO2, -halogen, and -CN, as well as heteroatoms such as S and O. This reduction procedure exhibited the recyclable and reusable property of heterogeneous catalysts and was applicable to gram-scale synthesis. The reaction mechanisms were proposed based on some control experiments and the previous literature. This is the first example of hydroborative reduction of amides to amines mediated by heterogeneous catalysts.
- Guo, Chenjun,Zhang, Fangcao,Yu, Chong,Luo, Yunjie
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supporting information
p. 13122 - 13135
(2021/08/31)
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- Progressing the Frustrated Lewis Pair Abilities of N-Heterocyclic Carbene/GaR3Combinations for Catalytic Hydroboration of Aldehydes and Ketones
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Exploiting the steric incompatibility of the tris(alkyl)gallium GaR3 (R = CH2SiMe3) and the bulky N-heterocyclic carbene (NHC) 1,3-bis(tert-butyl)imidazol-2-ylidene (ItBu), here we report the B-H bond activation of pinacolborane (HBPin), which has led to
- Bole, Leonie J.,Uzelac, Marina,Hernán-Gómez, Alberto,Kennedy, Alan R.,O'Hara, Charles T.,Hevia, Eva
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supporting information
p. 13784 - 13796
(2021/07/26)
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- FRUSTRATED LEWIS PAIR-IMPREGNATED POROUS MATERIALS AND USES THEREOF
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Described herein are compositions composed of frustrated Lewis pairs impregnated in porous materials such as, for example, metal-organic frameworks, and their uses thereof. These compositions may allow new applications of frustrated Lewis pairs in catalysis by sequestering and protecting the frustrated Lewis pair within the nanospace of the porous material. Also provided are methods of hydrogenating an organic compound having at least one unsaturated functional group comprising using the compositions described herein.
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Page/Page column 73; 78-80
(2021/01/23)
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- Iron-catalysed hydroboration of non-activated imines and nitriles: Kinetic and mechanistic studies
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Iron-catalysed hydroboration of imines and nitriles has been developed under low catalyst loading (1 mol%) in the presence of HBpin. A wide scope of substrate was found to smoothly undergo hydroboration, including electron releasing/withdrawing and haloge
- Bazkiaei, Adineh Rezaei,Wiseman, Michael,Findlater, Michael
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p. 15284 - 15289
(2021/05/19)
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- Hydroboration of carbonyls and imines by an iminophosphonamido tin(ii) precatalyst
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A novel three-coordinated tin(ii) chloride [Ph2P(NtBu)2]SnCl (1) supported by an N,N′-di-tert-butyliminophosphonamide having two phenyl groups on the phosphorus atom was synthesized by the reaction of the starting lithium iminophosphonamide [Ph2P(NtBu)2]L
- Nakaya, Kazuki,Takahashi, Shintaro,Ishii, Akihiko,Boonpalit, Kajjana,Surawatanawong, Panida,Nakata, Norio
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supporting information
p. 14810 - 14819
(2021/11/03)
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- Carbodiphosphorane-Catalyzed Hydroboration of Ketones and Imines
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We report the use of a cyclic carbodiphosphorane catalyst for ketone and imine hydroboration reactions. Ketone hydroboration reactions are particularly rapid, typically reaching completion within 15 min using a 1 mol % catalyst loading at 25 °C. To our knowledge, this represents the first use of a carbodiphosphorane as an organocatalyst. The carbodiphosphorane exhibited superior catalytic activity in comparison to other neutral carbon nucleophiles tested, including an N-heterocyclic carbene, an N-heterocyclic olefin, and phosphorus ylides.
- Aversa-Fleener, Cara R.,Chang, Daniel K.,Liberman-Martin, Allegra L.
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supporting information
p. 4050 - 4054
(2022/01/04)
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- Homoleptic Bis(trimethylsilyl)amides of Yttrium Complexes Catalyzed Hydroboration Reduction of Amides to Amines
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Homoleptic lanthanide complex Y[N(TMS)2]3 is an efficient homogeneous catalyst for the hydroboration reduction of secondary amides and tertiary amides to corresponding amines. A series of amides containing different functional groups such as cyano, nitro, and vinyl groups were found to be well-tolerated. This transformation has also been nicely applied to the synthesis of indoles and piribedil. Detailed isotopic labeling experiments, control experiments, and kinetic studies provided cumulative evidence to elucidate the reaction mechanism.
- Ye, Pengqing,Shao, Yinlin,Ye, Xuanzeng,Zhang, Fangjun,Li, Renhao,Sun, Jiani,Xu, Beihang,Chen, Jiuxi
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p. 1306 - 1310
(2020/02/22)
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- Synthesis and Reactivity of Fluorinated Triaryl Aluminum Complexes
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The addition of the Grignard 3,4,5-ArFMgBr to aluminum(III) chloride in ether generates the novel triarylalane Al(3,4,5-ArF)3·OEt2. Attempts to synthesize this alane via transmetalation from the parent borane with trimethylaluminum gave a dimeric structure with bridging methyl groups, a product of partial transmetalation. On the other hand, the novel alane Al(2,3,4-ArF)3 was synthesized from the parent borane and trimethylaluminum. Interestingly, the solid-state structure of Al(2,3,4-ArF)3 shows an extended chain structure resulting from neighboring Al···F contacts. Al(3,4,5-ArF)3·OEt2 was then found to be an effective catalyst for the hydroboration of carbonyls, imines, and alkynes with pinacolborane.
- Ould, Darren M. C.,Carden, Jamie L.,Page, Rowan,Melen, Rebecca L.
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supporting information
p. 14891 - 14898
(2020/10/02)
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- Alkali Metal–Promoted Facile Synthesis of Secondary Amines from Imines and Carbodiimides
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We present here an efficient method for the hydroboration of aldimines (-C=N-) with pinacolborane (HBpin) using an alkali metal catalyst, potassium benzyl. The reaction was accomplished with unprecedented catalytic efficiency under mild and solvent-free conditions to afford the high yield of the corresponding N-boryl amines up to 97percent. Various functionalities on aldimines were incorporated for hydroboration. The corresponding boryl amines were subjected to further hydrolysis to yield the corresponding secondary amines with good yields up to 89percent. This protocol for the reaction demonstrates an atom-economic and green method with diverse imines that bears excellent functional group tolerance. Chemoselective reduction of imines was also attained, with good yields of 74–89percent. We also propose the most plausible mechanism involving the formation of metal hydride as the active pre-catalyst.
- Panda, Tarun K.,Banerjee, Indrani,Sagar, Shweta
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- Application of three-metallocene rare earth complex in hydrogenation reaction of catalytic imine and borane
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The invention relates to application of a metal organic complex, in particular to application of a trimethyl cyclopentadienyl rare earth complex in catalysis of imine and borane hydrogenation reaction. A catalyst, borane and imine are mixed evenly in orde
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Paragraph 0028-0035
(2020/02/29)
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- Aluminum-Catalyzed Selective Hydroboration of Nitriles and Alkynes: A Multifunctional Catalyst
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The reaction of LH [L = {(ArNH)(ArN)-C=N-C=(NAr)(NHAr)}; Ar =2,6-Et2-C6H3] with a commercially available alane amine adduct (H3Al·NMe2Et) in toluene resulted in the formation of a conjugated bis-guanidinate (CBG)-supported aluminum dihydride complex, i.e., LAlH2 (1), in good yield. The new complex has been thoroughly characterized by multinuclear magnetic resonance, IR, mass, and elemental analyses, including single-crystal structural studies. Further, we have demonstrated the aluminum-catalyzed hydroboration of a variety of nitriles and alkynes. Moreover, aluminum-catalyzed hydroboration is expanded to more challenging substrates such as alkene, pyridine, imine, carbodiimide, and isocyanides. More importantly, we have shown that the aluminum dihydride catalyzed both intra- A nd intermolecular chemoselective hydroboration of nitriles and alkynes over other reducible functionalities for the first time.
- Sarkar, Nabin,Bera, Subhadeep,Nembenna, Sharanappa
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p. 4999 - 5009
(2020/05/01)
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- Method for preparing borate through hydroboration reaction
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The invention relates to a method for preparing borate by hydroboration reaction, which sequentially comprises the following steps: uniformly stirring and mixing a catalyst, borane and imine, reactingfor 1-2 hours, exposing in air to terminate the reactio
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Paragraph 0016-0020
(2020/07/13)
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- Erratum: Redox-Noninnocent Ligand-Supported Vanadium Catalysts for the Chemoselective Reduction of C=X (X = O, N) Functionalities (Journal of the American Chemical Society (2019) 141:38 (15230-15239) DOI: 10.1021/jacs.9b07062)
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Pages 15232, 15233, and 15236. In the original paper, the doublet wave functions for 21 and 21a/21b were incorrectly (Figure Presented). reported as spin-contaminated in sections 2.3 and 2.8 (Figure 3 and Scheme 9, respectively.) This comes from the incorrectly reported expected eigenvalue of 0.75 for the spin-squared operator ??2? for the antiferromagnetically coupled doublet |↓?L|↑↑?V state (originally given in the Supporting Information). The correct expected eigenvalue for the |↓?L|↑↑?V state should be 1.75. The wave functions for 21 and 21a/21b (eigenvalues 1.79 and 1.77/1.66, respectively) are therefore not spincontaminated. The corrected Figure 3 and Scheme 9 are presented below. A corrected Supporting Information file is also provided. The corrections do not affect any of the conclusions of the Article, but slightly decrease the gap between the quartet and doublet spin surfaces. Scheme 3 has been also corrected to reflect the fact that (CH3)3SiCH2 ? radicals can only react based on spin conservation.
- Zhang, Guoqi,Wu, Jing,Zheng, Shengping,Neary, Michelle C.,Mao, Jincheng,Flores, Marco,Trovitch, Ryan J.,Dub, Pavel A.
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supporting information
p. 16507 - 16509
(2020/10/14)
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- Catalyst-Free Reductive Coupling of Aromatic and Aliphatic Nitro Compounds with Organohalides
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A rare reductive coupling of nitro compounds with organohalides has been realized. The reaction is initiated by a partial reduction of the nitro group to a nitrenoid intermediate. Therefore, not only aromatic but also aliphatic nitro compounds are efficiently transformed into monoalkylated amines, with organohalides as the alkylating agent. Given the innate reactivity of the nitrenoid, a catalyst is not required, resulting in a high tolerance for aryl halide substituents in both starting materials.
- Rauser, Marian,Eckert, Raphael,Gerbershagen, Max,Niggemann, Meike
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supporting information
p. 6713 - 6717
(2019/04/14)
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- Unlocking the catalytic potential of tris(3,4,5-trifluorophenyl)borane with microwave irradiation
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The catalytic activity of tris(3,4,5-trifluorophenyl)borane has been explored in the 1,2-hydroboration reactions of unsaturated substrates. Under conventional conditions, the borane was found to be active only in the hydroboration of aldehyde, ketone and imine substrates, with alkenes and alkynes not being reduced effectively. The use of microwave irradiation on the other hand has permitted alkenes and alkynes to be hydroborated in good yields.
- Carden, Jamie L.,Gierlichs, Lukas J.,Wass, Duncan F.,Browne, Duncan L.,Melen, Rebecca L.
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supporting information
p. 318 - 321
(2019/01/09)
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- Catalyst-Free and Solvent-Free Facile Hydroboration of Imines
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A facile process for the catalyst-free and solvent-free hydroboration of aromatic as well as heteroaromatic imines is reported. This atom-economic methodology is scalable, compatible with sterically and electronically diverse imines, displaying excellent tolerance towards various functional groups, and works efficiently at ambient temperature in most of the cases, affording secondary amines in good to excellent yield after hydrolysis.
- Pandey, Vipin K.,Donthireddy, Siva Nagendra Reddy,Rit, Arnab
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supporting information
p. 3255 - 3258
(2019/09/17)
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- Application of p-methylaniline lithium in catalysis of hydroboration reaction of imine and borane
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The invention relates to an application of p-methylaniline lithium, and concretely relates to an application of p-methylaniline lithium in the catalysis of a hydroboration reaction of imine and borane. A catalyst, borane and imine are stirred and mixed un
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Paragraph 0016-0018; 0020
(2019/02/04)
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- Applications of anilino lithium in catalytic hydroboration reaction of imine and borane
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The invention relates to applications of anilino lithium, and more specifically relates to applications of anilino lithium in catalytic hydroboration reaction of imine and borane. According to a method, a catalyst, borane, and imine are stirred to be unif
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Paragraph 0012; 0015-0020
(2019/01/20)
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- Application of o-methylaniline lithium in catalysis of hydroboration reaction of imine and borane
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The invention relates to an application of o-methylaniline lithium, and concretely relates to an application of o-methylaniline lithium in the catalysis of a hydroboration reaction of imine and borane. A catalyst, borane and imine are stirred and mixed un
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Paragraph 0015-0019
(2019/02/08)
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- Application of 2,6-diisopropyl aniline lithium in catalyzing hydroboration of imine and borane
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The invention relates to an application of 2,6-diisopropyl aniline lithium and specifically relates to the application of 2,6-diisopropyl aniline lithium in catalyzing hydroboration of imine and borane. The application comprises the following steps: unifo
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Paragraph 0012; 0015-0020
(2019/02/04)
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- Catalytic Recycling of a Th-H Bond via Single or Double Hydroboration of Inactivated Imines or Nitriles
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The catalytic activity of the metallacycle thorium amide [(Me3Si)2N]2Th[κ2-(N,C)-CH2Si(CH3)2N(SiMe3)] (Th1) is presented for the selective dihydroboration of nitriles
- Saha, Sayantani,Eisen, Moris S.
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p. 5947 - 5956
(2019/06/17)
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- Metal-Organic Framework Anchored with a Lewis Pair as a New Paradigm for Catalysis
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Lewis pair (LP) chemistry has shown broad applications in the catalysis field. However, one significant challenge has been recognized as the instability for most homogeneous LP catalysts upon recycling, thus inevitably leading to dramatic loss in catalytic activity. Additionally, current heterogeneous LP catalysts suffer from low surface area, which largely limits their catalytic efficiency, thereby restricting their potential applications. In this work, we report the successful introduction of LPs, classical and frustrated, into a metal-organic framework (MOF) that features high surface and ordered pore structure via a stepwise anchoring strategy. Not only can the LP be stabilized by the strong coordination interaction between the LP and MOF, but the resultant MOF-LP also demonstrates excellent catalysis performance with interesting size and steric selectivity. Given the broad applicability of LPs, our work therefore paves a way for advancing MOF-LP as a new paradigm for catalysis. Lewis pairs (LPs), classical and frustrated, are excellent prospects in catalysis, organic syntheses, biology, and material sciences. However, the instability of most LP catalysts leads to a dramatic loss in activities, thereby largely restricting their industrial applications. As robust porous materials, metal-organic frameworks (MOFs) offer a platform to stabilize homogeneous catalysts. Here, we show a strategy that grafts the LP catalyst on the MOF to minimize loss of LPs during catalysis and recycling. Our work reveals the enormous potential of MOFs as an appealing paradigm for the construction of efficient heterogeneous catalysts with interesting steric and size selectivity worthy of exploration. In addition, the strategies for anchoring a LP into a MOF as contributed herein can be readily applied for the task-specific design of functional catalysis materials for various applications. Lewis pairs (LPs), classical and frustrated, have been successfully introduced into and stabilized in a metal-organic framework (MOF). Benefiting from the robust framework and tunable porous structure of MOFs, the resultant MOF-LP demonstrates not only great recyclability but also excellent performance in the catalytic reduction of imines and hydrogenation of alkenes. The combination of LP and MOF therefore lays a foundation for developing a MOF-LP as a new paradigm for catalysis, particularly heterogeneous catalysis.
- Niu, Zheng,Bhagya Gunatilleke, Wilarachchige D.C.,Sun, Qi,Lan, Pui Ching,Perman, Jason,Ma, Jian-Gong,Cheng, Yuchuan,Aguila, Briana,Ma, Shengqian
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p. 2587 - 2599
(2018/12/02)
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- Well-Defined Amidate-Functionalized N-Heterocyclic Carbene -Supported Rare-Earth Metal Complexes as Catalysts for Efficient Hydroboration of Unactivated Imines and Nitriles
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Four amidate-functionalized N-heterocyclic carbene (NHC) rare-earth metal amido complexes [(κ2-N,O-κ1-L)2REN(SiMe3)2] (L = 1-(C6H5CONCH2CH2)-3-(CH3)3C6H2(N(CH)2NC)) [RE = Er (1), Y (2), Dy (3), Gd (4)] were synthesized by one-pot reactions of 2 equiv of (1-(C6H5CONHCH2CH2)-3-(CH3)3C6H2-(N(CH)2NCH))Br (H2LBr) with 5 equiv of KN(SiMe3)3 followed by treatment with 1 equiv of RECl3 in tetrahydrofuran at -40 °C. These complexes were fully characterized, and their catalytic activities toward hydroboration of unactivated imines and nitriles were investigated, and it was found that these complexes displayed excellent activities as well as remarkable functional group compatibility for imine and nitrile substrates such as halo-, alkyl-, hydroxyl-, N,N-dimethylamino-, and nitro- substituents. Among those, the chemoselectivity for this reaction among the common unsaturated functional groups was achieved in the order CO CN > C=N > CO2Et > CC in the current catalytic system, which may facilitate their further application in synthetic chemistry.
- Huang, Zeming,Wang, Shaowu,Zhu, Xiancui,Yuan, Qingbing,Wei, Yun,Zhou, Shuangliu,Mu, Xiaolong
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supporting information
p. 15069 - 15078
(2018/12/14)
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- Highly efficient hydroboration of carbonyl compounds catalyzed by tris(methylcyclopentadienyl)lanthanide complexes
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Homoleptic lanthanide complexes coordinated by a Me-substituted Cp ligand [(MeCp)3Ln] demonstrate unprecedentedly high efficiency in catalyzing the hydroboration of aldehydes and ketones with pinacolborane. This protocol is also applicable for the hydroboration of aryl-substituted imines. In addition, broad functional group compatibility and excellent chemoselectivity is also achieved. DFT calculations are employed to shed light on the reaction mechanism.
- Yan, Dandan,Dai, Ping,Chen, Sufang,Xue, Mingqiang,Yao, Yingming,Shen, Qi,Bao, Xiaoguang
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p. 2787 - 2791
(2018/04/27)
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- Cobalt(II) Coordination Polymer as a Precatalyst for Selective Hydroboration of Aldehydes, Ketones, and Imines
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Highly effective hydroboration precatalyst is developed based on a cobalt(II)-terpyridine coordination polymer (CP). The hydroboration of ketones, aldehydes, and imines with pinacolborane (HBpin) has been achieved using the recyclable CP catalyst in the presence of an air-stable activator. A wide range of substrates containing polar C=O or C=N bonds have been hydroborated selectively in excellent yields under ambient conditions.
- Wu, Jing,Zeng, Haisu,Cheng, Jessica,Zheng, Shengping,Golen, James A.,Manke, David R.,Zhang, Guoqi
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p. 9442 - 9448
(2018/07/05)
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- P-N Cooperative Borane Activation and Catalytic Hydroboration by a Distorted Phosphorous Triamide Platform
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Studies of the stoichiometric and catalytic reactivity of a geometrically constrained phosphorous triamide 1 with pinacolborane (HBpin) are reported. The addition of HBpin to phosphorous triamide 1 results in cleavage of the B-H bond of pinacolborane through addition across the electrophilic phosphorus and nucleophilic N-methylanilide sites in a cooperative fashion. The kinetics of this process of were investigated by NMR spectroscopy, with the determined overall second-order empirical rate law given by ν = -k[1][HBpin], where k = 4.76 × 10-5 M-1 s-1 at 25 °C. The B-H bond activation process produces P-hydrido-1,3,2-diazaphospholene intermediate 2, which exhibits hydridic reactivity capable of reacting with imines to give phosphorous triamide intermediates, as confirmed by independent synthesis. These phosphorous triamide intermediates are typically short lived, evolving with elimination of the N-borylamine product of imine hydroboration with regeneration of the deformed phosphorous triamide 1. The kinetics of this latter process are shown to be first-order, indicative of a unimolecular mechanism. Consequently, catalytic hydroboration of a variety of imine substrates can be realized with 1 as the catalyst and HBpin as the terminal reagent. A mechanistic proposal implicating a P-N cooperative mechanism for catalysis that incorporates the various independently verified stoichiometric steps is presented, and a comparison to related phosphorus-based systems is offered.
- Lin, Yi-Chun,Hatzakis, Emmanuel,McCarthy, Sean M.,Reichl, Kyle D.,Lai, Ting-Yi,Yennawar, Hemant P.,Radosevich, Alexander T.
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p. 6008 - 6016
(2017/05/04)
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- BArF3-Catalyzed Imine Hydroboration with Pinacolborane Not Requiring the Assistance of an Additional Lewis Base
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The rarely used boron Lewis acid tris[3,5-bis(trifluoromethyl)phenyl]borane (BArF3) is found to be an excellent catalyst for metal-free hydroboration of imines. In the presence of 1.0 mol % of BArF3, several ketimines and aldimines undergo hydroboration with pinacolborane (HBpin) at room temperature without the aid of an external Lewis base. BArF3 is more reactive than other Lewis acidic boranes, including the often-used tris(pentafluorophenyl)borane (B(C6F5)3). The steric hindrance imparted by the six fluorine atoms ortho to the boron center in B(C6F5)3 accounts for this. Mechanistic control experiments indicate conventional Lewis acid catalysis involving imine activation and hydride transfer from HBpin.
- Yin, Qin,Soltani, Yashar,Melen, Rebecca L.,Oestreich, Martin
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supporting information
p. 2381 - 2384
(2017/07/17)
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- Tris(2,4,6-trifluorophenyl)borane: An Efficient Hydroboration Catalyst
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The metal-free catalyst tris(2,4,6-trifluorophenyl)borane has demonstrated its extensive applications in the 1,2-hydroboration of numerous unsaturated reagents, namely alkynes, aldehydes and imines, consisting of a wide array of electron-withdrawing and donating functionalities. A range of over 50 borylated products are reported, with many reactions proceeding with low catalyst loading under ambient conditions. These pinacol boronate esters, in the case of aldehydes and imines, can be readily hydrolyzed to leave the respective alcohol and amine, whereas alkynyl substrates result in vinyl boranes. This is of great synthetic use to the organic chemist.
- Lawson, James R.,Wilkins, Lewis C.,Melen, Rebecca L.
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supporting information
p. 10997 - 11000
(2017/08/22)
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- Transition metal free catalytic hydroboration of aldehydes and aldimines by amidinato silane
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The transition metal free catalytic hydroboration of aldehydes and ketones is very limited and has not been reported with a well-defined silicon(iv) compound. Therefore, we chose to evaluate the previously reported silicon(iv) hydride [PhC(NtBu)2SiHCl2], (1) as a single component catalyst and found that it catalyzes the reductive hydroboration of a range of aldehydes with pinacolborane (HBpin) under ambient conditions. In addition, compound 1 can catalyze imine hydroboration. DFT calculation was carried out to understand the mechanism.
- Bisai, Milan Kumar,Pahar, Sanjukta,Das, Tamal,Vanka, Kumar,Sen, Sakya S.
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p. 2420 - 2424
(2017/03/08)
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- Zinc hydridotriphenylborates supported by a neutral macrocyclic polyamine
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The zinc hydridotriphenylborates [(L)Zn(TMDS)][HBPh3] and [(L)ZnX][HBPh3] (L = Me4TACD, Me4[12]aneN4; TMDS = N(SiHMe2)2; X = Cl, Br, I) were synthesized by BPh3-mediated β-SiH abstraction and salt metathesis with KHBPh3, respectively. CO2 is rapidly inserted into the B-H bonds. [(L)Zn(TMDS)][HBPh3] catalyzes the hydroboration of polar substrates including CO2.
- Mukherjee, Debabrata,Wiegand, Ann-Kristin,Spaniol, Thomas P.,Okuda, Jun
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supporting information
p. 6183 - 6186
(2017/07/11)
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- Rhenium-catalysed hydroboration of aldehydes and aldimines
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The first examples for the rhenium-catalysed hydroboration of aldehydes, ketones and aldimines, including heteroaromatic quinoline, are reported herein. Reactions are remarkably chemoselective and tolerant of several functional groups. A wide array of rhenium complexes were efficient pre-catalysts for these hydroborations, including new low-valent complexes of the formula [Re(N-N)(CO)3(L)]X (N-N = bipy derivative, L = labile ligand/solvent, and X = [BArF4]- and [B(3,5-di-tBu-cat)2]-), which have been characterized fully including an X-ray diffraction study for [Re(bipy)(CO)3(quin)][BArF4] (2). A new silver spiroboronate ester Ag[B(3,5-di-tBu-cat)2](NCCH3)3 (3) was prepared and characterized fully, including an X-ray diffraction study, and used to make one of the new rhenium complexes.
- Arévalo, Rebeca,Vogels, Christopher M.,Macneil, Gregory A.,Riera, Lucía,Pérez, Julio,Westcott, Stephen A.
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supporting information
p. 7750 - 7757
(2017/07/11)
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- Metal-Organic Framework Nodes Support Single-Site Magnesium-Alkyl Catalysts for Hydroboration and Hydroamination Reactions
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Here we present the first example of a single-site main group catalyst stabilized by a metal-organic framework (MOF) for organic transformations. The straightforward metalation of the secondary building units of a Zr-MOF with Me2Mg affords a hi
- Manna, Kuntal,Ji, Pengfei,Greene, Francis X.,Lin, Wenbin
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p. 7488 - 7491
(2016/07/06)
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- Ni(bpy)(cod): A Convenient Entryway into the Efficient Hydroboration of Ketones, Aldehydes, and Imines
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The catalytic hydroboration of ketones, aldehydes, and imines with pinacol borane and Ni(bpy)(cod) has been demonstrated in benzene at room temperature and low catalyst loadings (0.03-0.3 mol-%). Spectroscopic and structural evidence support the formulati
- King, Amanda E.,Stieber, S. Chantal E.,Henson, Neil J.,Kozimor, Stosh A.,Scott, Brian L.,Smythe, Nathan C.,Sutton, Andrew D.,Gordon, John C.
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supporting information
p. 1635 - 1640
(2016/05/02)
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- Ruthenium-Catalyzed Selective Hydroboration of Nitriles and Imines
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Ruthenium-catalyzed hydroboration of nitriles and imines is attained using pinacolborane with unprecedented catalytic efficiency. Chemoselective hydroboration of nitriles over esters is also demonstrated. A simple [Ru(p-cymene)Cl2]2 complex (1) is used as a catalyst precursor, which upon reaction with pinacolborane in situ generates the monohydrido-bridged complex [{(η6-p-cymene)RuCl}2(μ-H-μ-Cl)] 2. Further oxidative addition of pinacolborane to intermediate 2 leading to the formation of mononuclear ruthenium hydride species is suggested. Mass spectral analysis of the reaction mixture and independent experiments with phosphine-ligated ruthenium complexes indicated the involvement of mononuclear ruthenium intermediates in the catalytic cycle. Consecutive intramolecular 1,3-hydride transfers from the ruthenium center to coordinated nitrile and boronate imine ligands, leading to the reduction and resulting in the formation of diboronate amines, are proposed as a plausible reaction mechanism.
- Kaithal, Akash,Chatterjee, Basujit,Gunanathan, Chidambaram
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p. 11153 - 11163
(2016/11/28)
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- Magnesium hydridotriphenylborate [Mg(thf)6][HBPh3]2: A versatile hydroboration catalyst
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Magnesium bis(hydridotriphenylborate), isolated as a solvent-separated ion pair [Mg(thf)6][HBPh3]2, effectively catalyzed the hydroboration of several unsaturated substrates including CO2.
- Mukherjee, Debabrata,Shirase, Satoru,Spaniol, Thomas P.,Mashima, Kazushi,Okuda, Jun
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supporting information
p. 13155 - 13158
(2016/11/09)
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- Reactivity of a Molecular Magnesium Hydride Featuring a Terminal Magnesium-Hydrogen Bond
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The reactivity of the molecular magnesium hydride [Mg(Me3TACD·AliBu3)H] (1) featuring a terminal magnesium-hydrogen bond and an NNNN-type macrocyclic ligand, Me3TACD ((Me3TACD)H = Me3[12]aneN4 = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane), can be grouped into protonolysis, oxidation, hydrometalation, (insertion), and hydride abstraction. Protonolysis of 1 with weak Br?nsted acids HX such as terminal acetylenes, amines, silanols, and silanes gave the corresponding derivatives [Mg(Me3TACD·AliBu3)X] (X = C=CPh, 3; HN(3,5-Me2-C6H3), 4; OSiMe3, 5; OSiPh3, 6; Cl, 7; Br, 8). Single-crystal X-ray diffraction of anilide 4 showed a square-pyramidal coordination geometry for magnesium. No correlation with the pKa values of the acids was detected. Oxidation of 1 with elemental iodine gave the iodide [Mg(Me3TACD·AliBu3)I] (9), and oxidation with nitrous oxide afforded the μ-oxo-bridged compound [{Mg(Me3TACD·AliBu3)}2(μ-O)] (10) with a linear Mg-O-Mg core, as characterized by single-crystal X-ray diffraction. The Mg-H bond reacted with benzaldehyde, benzophenone, fluorenone, and CO2 under insertion but not with the olefins 1,1,2-triphenylethylene, tert-butylethylene, and cyclopentene. The unstable formate, prepared also by salt metathesis of iodide 9 with potassium formate, revealed ?°O,?°O′ coordination in the solid state. Hydride abstraction with triphenylborane gave the ion pair [Mg(Me3TACD·AliBu3)(thf)][HBPh3] (16), which catalyzed the hydroboration of polar substrates by pinacolborane.
- Schnitzler, Silvia,Spaniol, Thomas P.,Okuda, Jun
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p. 12997 - 13006
(2016/12/26)
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- Magnesium catalysis of imine hydroboration
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The β-diketiminato magnesium alkyl complex [LMgnBu] (L=CH{CMe(NDipp)}2, Dipp=diisopropylphenyl) is shown to be a highly effective precatalyst for the hydroboration of alkyl and aryl substituted aldimines and ketimines with pinacol borane (HBpin). Catalysis is proposed to occur through a sequence of Mg-N/B-H metathesis and rate-determining Mg-H/N=C insertion steps, a proposal strongly supported by stoichiometric studies and kinetic analysis. The reactions are observed to proceed through the intermediacy of well-defined magnesium amides, two examples of which have been isolated and structurally characterized. Mechanistic investigations suggest that the catalytic rate-determining process occurs at an isolated magnesium center and requires the presence of two molecules of the imine substrate for effective turnover. This latter observation is rationalized as a requirement for the secondary substrate molecule to displace HBpin from the coordination sphere of the catalytic magnesium center.
- Arrowsmith, Merle,Hill, Michael S.,Kociok-Koehn, Gabriele
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p. 2776 - 2783
(2013/03/14)
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- Taking the F out of FLP: Simple lewis acid-base pairs for mild reductions with neutral boranes via borenium ion catalysis
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Discrete three-coordinate borenium salts 1c and 1d are accessed by cooperative Lewis acid-base pair-mediated heterolytic splitting of the B-H bond in pinacolborane by B(C6F5)3DABCO and Ph 3C+/DABCO, respectively. The resulting salts are competent catalysts in the reduction of a broad range of imines and can be generated in situ. Moreover, a mechanistic framework for borenium catalysis based on experimental evidence is proposed. The reaction is suggested to proceed by borenium activation of the imine substrate followed by counterintuitive hydride delivery from HBPin (with the assistance of DABCO) rather than from the HB(C6F5)3- anion, contrary to typical mechanisms of reduction in FLP systems.
- Eisenberger, Patrick,Bailey, Adrian M.,Crudden, Cathleen M.
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p. 17384 - 17387
(2013/01/15)
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