Asymmetric homogeneous hydrogenation catalyzed by a cobalt complex.  High enantiomeric excess via statistically designed experiments and mechanistic studies

Waldron, Richard W.; Weber, James H.

doi:10.1021/ic50171a049

Cited by 34 publications

(5 citation statements)

References 9 publications

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“…24, 25 Ohgo and Weber developed a cobalt–dioxime‐based system that catalyzed the asymmetric hydrogenation of benzil, but the substrate scope was limited to selected 1,2‐dicarbonyl compounds 26. 27 Thus, we were surprised to find that cobalt precatalyst 2 was quite active for hydrogenation of both aldehydes and ketones under mild conditions.…”

Section: Methodsmentioning

confidence: 99%

Mild and Homogeneous Cobalt‐Catalyzed Hydrogenation of CC, CO, and CN Bonds

2012

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The replacement of precious-metal catalysts with cheap and abundant metals is a major goal of sustainable chemistry. [1] Hydrogenation catalysts have diverse and widespread applications, including the production of biorenewable chemicals and fuels, commodity chemicals, and the synthesis of fine chemicals and pharmaceuticals. [2][3][4] Homogeneous rhodium, ruthenium, and iridium catalysts are also of critical importance in asymmetric hydrogenation. [5] Despite significant recent advances, the design of earth-abundant-metal hydrogenation catalysts has lagged behind, perhaps because of the tendency of 3d metals to engage in one-electron or radical chemistry. Several iron catalysts have been developed for the hydrogenation of ketones or alkenes, but they are typically chemoselective, reducing only one class of substrate. [6][7][8][9] Furthermore, iron catalysts are often quite sensitive to additional oxygen-and nitrogen-containing functional groups and water. [10] There is growing evidence that cobalt complexes can be effective catalysts for homogeneous hydrogenation. Cobalt(I) complexes, such as [Co(H)(CO) 4 ] and [Co(H)(CO)(PnBu 3 ) 3 ], are known to catalyze the hydrogenation of alkenes and arenes under hydroformylation conditions (> 120 8C, > 30 atm H 2 /CO). [11][12][13] Diiminopyridine cobalt complexes and the dinitrogen complex [Co(H)(N 2 )(PPh 3 ) 3 ] catalyze olefin hydrogenation at room temperature, [14,15] and an asymmetric hydrogenation of substituted styrenes was recently developed. [16] However, prior examples of cobalt hydrogenation catalysts have been quite limited in substrate scope, and nearly all have involved cobalt(I). [17,18] Herein, we report a cobalt-based catalytic system for the homogeneous hydrogenation of alkenes, aldehydes, ketones, and imines. The hydrogenation reactions take place under very mild conditions and require no base additives. The ability to hydrogenate multiple classes of substrates and broad functional-group tolerance make this cobalt system a significant advance over previously reported earth-abundant-metal hydrogenation catalysts.We synthesized cobalt(II) complexes of the tridentate ligand bis[2-(dicyclohexylphosphino)ethyl]amine (PNHP Cy ) (Scheme 1). Previous work by Fryzuk et al. had shown that a related pincer amidodiphosphine ligand stabilized a squareplanar 15-electron d 7 -cobalt(II)-alkyl complex, [19] and we were interested in exploring the reactivity of this type of unusual odd-electron cobalt-alkyl species. Reaction of PNHP Cy with [(pyr) 2 Co(CH 2 SiMe 3 ) 2 ] [20] (pyr = pyridine) afforded the new cobalt(II)-alkyl complex [(PNP Cy )Co-(CH 2 SiMe 3 )] (1) as dark-yellow crystals. In the solid state, paramagnetic complex 1 has a square-planar geometry, and solution-state magnetic-moment measurements are also consistent with a square-planar low-spin d 7 configuration (m eff = 2.2 m B ). [21,22] The solution-state magnetic moment of complex 1 is quite similar to that of the related square-planar complex [(N(SiMe 2 CH 2 PPh 2 ) 2 )Co(CH 2 SiMe 3 )] (2.

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Section: Methodsmentioning

confidence: 99%

Mild and Homogeneous Cobalt‐Catalyzed Hydrogenation of CC, CO, and CN Bonds

2012

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“…The mechanistic of the reaction was studied by Waldron and Weber 90 and essentially confirmed by Ohgo. 91 The Co(II) precatalyst splits H 2 homolytically to give a Co(III) hydride that is then deprotonated by the chiral base (quinine, Q).…”

Section: Scheme 18 Ohgo's Catalyst For the Direct Asymmetric Hydrogenmentioning

confidence: 91%

“…89 Further efforts to improve the enantioselectivity were unsuccessful, and the scope has never been expanded to substituted benzils. 90…”

Section: Metal-catalyzed Hemihydrogenation Of Benzilsmentioning

confidence: 99%

Catalytic Strategies to Enantiopure Benzoins: Past and Future

Luca¹,

Mezzetti

2019

Synthesis

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The catalytic strategies developed so far for the synthesis of enantiomerically pure benzoins are reviewed. Particular attention is given to their substrate scope and limitations. Finally, this short review highlights the advantages of more atom-economic methods that have been reported recently.1 Introduction2 Benzoin Condensation2.1 Nucleophilic Carbenes as Catalysts2.2 Homocondensation of Aromatic Aldehydes2.3 Cross-Benzoin Condensation2.4 Acyloin Condensation2.5 Biocatalytic Methods3 Organocatalytic Friedel–Crafts Reaction4 Oxidative Methods4.1 α-Hydroxylation of Ketones4.2 Ketohydroxylation of Alkenes4.3 Enantiospecific Oxidation of meso-Hydrobenzoins4.4 Kinetic Resolution of Racemic Hydrobenzoins4.5 Biocatalytic Dynamic Kinetic Resolution5 Asymmetric Hemireduction of Benzils5.1 Biocatalytic Reductions – A Brief Summary5.2 Piers Hydrosilylation of Benzils5.3 Photoreduction of Benzils to Benzoins5.4 Metal-Catalyzed Hemihydrogenation of Benzils6 Conclusion and Future Challenges

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“…The asymmetric hydrogenation of prochiral ketones is one of the most useful synthetic methods to prepare optically active alcohols. , However, only a few examples using a chiral cobalt catalyst for the asymmetric hydrogenation of ketones have been reported to date. Early work by Ohgo and co-workers as well as Waldron and Weber in the 1970s and early 1980s described the use of two analogous quadridentate N -coordinated cobalt complexes Co-95 and Co-115 (Scheme ), respectively, for the hydrogenation of diketone substrates (e.g., benzil) in the presence of the chiral alkaloid quinine. ,− Co-95 catalyzed the asymmetric reduction of benzil to benzoin in 62% ee under 1 atm of H 2 at room temperature, whereas Co-115 achieved a higher ee value of 79% for the same reaction under similar conditions. It was proposed that quinine associated with the diketone substrate, making it more susceptible to nucleophilic attack by the cobalt metal center.…”

Section: Cobalt-catalyzed Hydride Transfer Reactionsmentioning

confidence: 99%

Hydride Transfer Reactions Catalyzed by Cobalt Complexes

et al. 2018

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Cobalt has become increasingly attractive in homogeneous catalysis because of its unique characteristics and outstanding catalytic performance in addition to being cheap and earth-abundant. Hydride transfer processes are involved in a broad range of organic transformations that allow the facile preparation of various useful chemicals and synthetic building blocks. These reactions have continuously received great attention both from academia and industry. In this perspective, we review homogeneous cobalt-catalyzed hydride transfer reactions according to the classified reaction types and provide a comprehensive overview of the design, synthesis, and reactivity of cobalt catalysts, their catalytic applications, and reaction mechanisms.

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Asymmetric homogeneous hydrogenation catalyzed by a cobalt complex. High enantiomeric excess via statistically designed experiments and mechanistic studies

Cited by 34 publications

References 9 publications

Mild and Homogeneous Cobalt‐Catalyzed Hydrogenation of CC, CO, and CN Bonds

Mild and Homogeneous Cobalt‐Catalyzed Hydrogenation of CC, CO, and CN Bonds

Catalytic Strategies to Enantiopure Benzoins: Past and Future

Hydride Transfer Reactions Catalyzed by Cobalt Complexes

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