The open d-shell enforces the active space in 3d metal catalysis: highly enantioselective chromium(<scp>ii</scp>) pincer catalysed hydrosilylation of ketones

Schiwek, Christian H.; Vasilenko, Vladislav; Wadepohl, Hubert; Gade, Lutz H.

doi:10.1039/c8cc05172k

Cited by 20 publications

(9 citation statements)

References 48 publications

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“…The spin density distribution in the four-coordinate, divalent iron complex with a 1,3-bis(2pyridylimino)isoindolines ligand was examined by means of 13 C NMR spectroscopy. 208 Iron, cobalt, and manganese complexes with this family of ligands were utilized in enantioselective ketone reduction, 209 enantioselective ketone hydrosilylation, 210,211 and enantioselective ketone hydroboration. 212,213 2.1.3.…”

Section: Privileged Pincer Platformsmentioning

confidence: 99%

First-Row Transition Metal (De)Hydrogenation Catalysis Based On Functional Pincer Ligands

2018

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The use of 3d metals in de-/hydrogenation catalysis has emerged as a competitive field with respect to 'traditional' precious metal catalyzed transformations. The introduction of functional pincer ligands that can store protons and/or electrons as expressed by metal-ligand cooperativity and ligand redox-activity strongly stimulated this development as conceptual starting point for rational catalyst design. This reviews aims at providing a comprehensive picture of the utilization of functional pincer ligands in first-row transition metal hydrogenation and dehydrogenation catalysis and related synthetic concepts relying on these such as the hydrogen borrowing methodology. Particular emphasis is put on the implementation and relevance of cooperating and redox-active pincer ligands within the mechanistic scenarios.

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Section: Privileged Pincer Platformsmentioning

confidence: 99%

First-Row Transition Metal (De)Hydrogenation Catalysis Based On Functional Pincer Ligands

2018

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“…In conclusion, we have demonstrated the existence of redox non‐innocence of hfac − through the spontaneous reduction by Cr II . Cr II complexes are well‐known to be highly efficient catalysts for example, the arylation and hydrosilylation of ketones, hydrogenation of polycyclic aromatic hydrocarbons, and C−C cross‐couplings . Unfortunately, the unknown exact chemical nature of most of these catalyst complexes and the intermediates preclude an evaluation of their electronic structures.…”

Section: Figurementioning

confidence: 99%

Evidence for Non‐Innocence of a β‐Diketonate Ligand

Vinum

Voigt

Bell

et al. 2020

Chemistry A European J

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β‐Diketonates, such as acetylacetonate, are amongst the most common bidentate ligands towards elements across the entire periodic table and are considered wholly redox‐inactive in their complexes. Herein we show that complexation of 1,1,1,5,5,5‐hexafluoroacetylacetonate (hfac−) to CrII spontaneously affords CrIII and a reduced β‐diketonate radical ligand scaffold, as evidenced by crystallographic analysis, magnetic measurements, optical spectroscopy, reactivity studies, and DFT calculations. The possibility of harnessing β‐diketonates as electron reservoirs opens up possibilities for new metal–ligand concerted reactivity in the ubiquitous β‐diketonate coordination chemistry.

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“…In agreement with experimental data, [Cr(POCOP-tBu)(NO)(κ 2 -BH4)] (4) adopts a doublet rather than a quintet ground state. Since a Cr(II) alkyl complex was recently shown to be catalytically active for the hydrosilylation of ketones, 15 we begun to investigate the potential the Cr(II) PCP alkyl complex 6 as catalyst for this transformation. Complex 6 (0.5 mol % based on ketones) was reacted with both aromatic and aliphatic ketones and (MeO)3SiH (1.2 equiv) in toluene (3 mL) at 25 °C.…”

Section: Scheme 2 Synthesis Of Complexes 3 Andmentioning

confidence: 99%

Cr(II) and Cr(I) PCP Pincer Complexes: Synthesis, Structure, and Catalytic Reactivity

et al. 2019

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In the current investigation, the reaction of [Cr(CO)6] with the ligand precursor PO(C-Br)OP-tBu (1) was investigated. When a suspension of [Cr(CO)6] and 1 in toluene was transferred into a sealed microwave glass vial and stirred for 3 h at 180 o C the square-planar Cr(II) complex [Cr(POCOP-tBu)Br] (2) was obtained. Treatment of 2 with 1 equiv of Li[HBEt3] in THF led to the formation of the borohydride complex [Cr(POCOP-tBu)(κ 2-BH4)] (3). Exposure of a toluene solution of 3 to NO gas (1 bar) at room temperature affords the Cr(I) complex [Cr(POCOP-tBu)(NO)(κ 2-BH4)] (4). Alternatively, 4 was also obtained by reacting [Cr(POCOP-tBu)(NO)(Br)] (5) with Li[HBEt3]. Based on magnetic and EPR measurements as well as DFT calculations, compounds 4 and 5 adopt a low-spin d 5 configuration and feature a nearly linear bound NO ligand suggesting Cr I NO + rather than Cr II NO • character. The reaction of 2 with 1 equiv of LiCH2SiMe3 in toluene afforded the square planar alkyl complex [Cr(POCOP-tBu)(CH2SiMe3] (6) in 57% yield. This compound is catalytically active for the hydrosilylation of ketones at room temperature with a catalyst loading of 0.5 mol%. X-ray structures of all complexes are presented.

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The open d-shell enforces the active space in 3d metal catalysis: highly enantioselective chromium(ii) pincer catalysed hydrosilylation of ketones

Cited by 20 publications

References 48 publications

First-Row Transition Metal (De)Hydrogenation Catalysis Based On Functional Pincer Ligands

First-Row Transition Metal (De)Hydrogenation Catalysis Based On Functional Pincer Ligands

Evidence for Non‐Innocence of a β‐Diketonate Ligand

Cr(II) and Cr(I) PCP Pincer Complexes: Synthesis, Structure, and Catalytic Reactivity

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