Cobalt-Catalyzed Asymmetric Hydrogenation of Vinylsilanes with a Phosphine–Pyridine–Oxazoline Ligand: Synthesis of Optically Active Organosilanes and Silacycles

Zuo, Ziqing; Xu, Songgen; Zhang, Lei; Gan, Lan; Fang, Huaquan; Liu, Guixia; Huang, Zheng

doi:10.1021/acs.organomet.9b00067

Cited by 29 publications

(17 citation statements)

References 65 publications

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“…As a result, employing PNN-L20 in the Ir-catalyzed ADH reaction only gave moderate enantioselectivity. In the same year, Huang and Liu 122 reported a chiral phosphine-oxazoline ligand (PNN-L21) that shares the same skeleton with PNN-L16. PNN-L21 was effective in Co-catalyzed ADH of vinylsilanes.…”

Section: Pnn-type Ligandsmentioning

confidence: 99%

Chiral Tridentate Ligands in Transition Metal-Catalyzed Asymmetric Hydrogenation

2021

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Asymmetric hydrogenation (AH) of double bonds has been one of the most effective methods for the preparation of chiral molecules and for the synthesis of important chiral building blocks. In the past 60 years, noble metals with bidentate ligands have shown marvelous reactivity and enantioselectivity in asymmetric hydrogenation of a series of prochiral substrates. In recent years, developing chiral tridentate ligands has played an increasingly important role in AH. With modular frameworks and a variety of functionalities on the side arms, chiral tridentate ligand complexes enable both reactivities and stereoselectivities. Although great achievements have been made for noble metal catalysts with chiral tridentate ligands since the 1990s, the design of chiral tridentate ligands for earth abundant metal catalysts has still been in high demand. This review summarizes the development of chiral tridentate ligands for homogeneous asymmetric hydrogenation. The philosophy of ligand design and the reaction mechanisms are highlighted and discussed as well.

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Section: Pnn-type Ligandsmentioning

confidence: 99%

Chiral Tridentate Ligands in Transition Metal-Catalyzed Asymmetric Hydrogenation

2021

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“…In the area of cobalt chemistry, reports from several groups have described the catalytic hydrogenation activity of well-defined cobalt catalysts featuring pincer ligands. − These catalysts have been applied successfully for the hydrogenation of olefins and semi-hydrogenation of alkynes, with several systems displaying impressive stereoselectivities. Despite this success, no unified mechanistic picture has arisen comparable to the better understood features of H 2 activation and olefin insertion at play with heavier Group 9 metals.…”

Section: Introductionmentioning

confidence: 99%

Catalytic Hydrogenation of Alkenes and Alkynes by a Cobalt Pincer Complex: Evidence of Roles for Both Co(I) and Co(II)

2021

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The Co(I) complex, [Co(N 2 )( Cy PNP)] ( Cy PNP = anion of 2,5-bis-(dicyclohexylphosphinomethyl)pyrrole), is active toward the catalytic hydrogenation of terminal alkenes and the semi-hydrogenation of internal alkynes under 2 bar of H 2 (g) at room temperature. The products of alkyne semi-hydrogenation are a mixture of E-and Z-alkenes. By contrast, use of the related cobalt(I) precatalyst, [Co(PMe 3 )-( Cy PNP)], results in formation of exclusively Z-alkenes. A semi-stable Co(II) species, [CoH( Cy PNP)], can also be generated by treatment of degassed solutions of [Co(N 2 )( Cy PNP)] with H 2 . The Co II -hydride displays activity toward both alkene hydrogenation and isomerization, but its instability hampers implementation as a catalyst. Several species relevant to potential catalytic intermediates have been isolated and detected in solution. These compounds include alkene and alkyne adducts of Co(I) as well as a Co(III) dihydride species. Catalytic results with the compounds examined are most consistent with a process involving shuttling between Co(I) and Co(III) states. However, generation of small quantities of Co(II) during catalytic turnover appears to be responsible for the isomerization observed for alkyne semi-hydrogenation. The interplay of cobalt oxidation states within the same catalyst system is discussed in the context of mechanistic scenarios for catalytic hydrogenation.

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“…The asymmetric hydrogenation of prochiral vinyl boronates is an attractive alternative for the preparation of enantioenriched building blocks and has been explored previously, principally with precious metal catalysts. , Such transformations can be powerful given the array of transformations for the preparation of vinyl boronates . Most recently, Lu described a class of sequential asymmetric hydrometalation–hydrogenation reactions utilizing C 1 -symmetric, enantioenriched cobalt dihalide complexes activated in situ by borohydride reagents .…”

Section: Introductionmentioning

confidence: 99%

A Boron Activating Effect Enables Cobalt-Catalyzed Asymmetric Hydrogenation of Sterically Hindered Alkenes

et al. 2020

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Unsymmetric 1,1-diboryl alkenes bearing one −[BPin] (BPin = pinacolatoboryl) and one −[BDan] (BDan = 1,8diaminonaphthalatoboryl) substituent each were hydrogenated in high yield and enantioselectivity using C 1 -symmetric pyridine-(diimine) (PDI) cobalt complexes. High activities and stereoselectivities were observed with an array of 2-alkyl-, 2-aryl-, and 2boryl-substituted 1,1-diboryl alkenes, giving rise to enantioenriched diborylalkane building blocks. Systematic study of substrate substituent effects identified competing steric and electronic demands in the key activating role of the boron substituents, whereby sterically unencumbered boronates such as −[BDan], −[BCat] (BCat = catecholatoboryl), and −[Beg] (Beg = ethylene glycolatoboryl) promote the hydrogenation of trisubstituted alkenes by enabling irreversible α-boron-directed insertion pathways to achieve otherwise challenging hydrogenations of trisubstituted alkenes. Deuterium-labeling studies with 1,1-diboryl alkenes support an insertion pathway generating a chiral intermediate with two different boron substituents and cobalt bound to the same carbon.

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Cobalt-Catalyzed Asymmetric Hydrogenation of Vinylsilanes with a Phosphine–Pyridine–Oxazoline Ligand: Synthesis of Optically Active Organosilanes and Silacycles

Cited by 29 publications

References 65 publications

Chiral Tridentate Ligands in Transition Metal-Catalyzed Asymmetric Hydrogenation

Chiral Tridentate Ligands in Transition Metal-Catalyzed Asymmetric Hydrogenation

Catalytic Hydrogenation of Alkenes and Alkynes by a Cobalt Pincer Complex: Evidence of Roles for Both Co(I) and Co(II)

A Boron Activating Effect Enables Cobalt-Catalyzed Asymmetric Hydrogenation of Sterically Hindered Alkenes

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