Hydrosilylation of Carbonyl Compounds Catalyzed by a Nickel Complex Bearing a PBP Ligand

Abstract

The efficient catalytic hydrosilylation of ketones and aldehydes has been investigated using a nickel pincer hydride complex supported by a diphosphino‐boryl ligand (PBP). It was found that the presence of the boryl group within the skeleton of the ligand has a beneficial effect on the catalytic activities observed for ketones compared to related pincer systems. The analysis of the reaction mechanism allows for the synthesis and characterization of a nickel alkoxide derivative by insertion of the carbonyl moiety into the Ni−H bond. Combined experimental and theoretical analysis (DFT) support a reaction mechanism that involves the initial formation of an alkoxide complex followed by reaction with the silane to release the corresponding silyl ether and regenerate the catalyst.

PCP Pincer Carbene Nickel(II) Chloride, Hydride, and Thiolate Complexes: Hydrosilylation of Aldehyde, Ketone, and Nitroarene by the Thiolate Complex

“…Further, the hydrosilylation of ketones by nickel pincer complexes has been scarcely studied. ,, The performance of complex 3 is greater than some of the reported complexes. For example, the secondary alcohol formation from acetophenone is much better (78%, 2.5 mol %, 8 h, 70 °C) than the activity of the reported complexes for the same product: [( i Pr POCOP)­NiH] (18%, 1.0 mol %, 24 h, 70 °C), [( t Bu PBP)­NiH] (56%, 5.0 mol %, 6 h, 70 °C), and [(Cp*-NHC Me )­NiO t Bu] (77%, 2.0 mol %, 24 h, 100 °C) . However, complex 3 exhibits less activity than does the platinum thiolate complex [{B­(NCH 2 P t Bu 2 ) 2 –1,2-C 6 H 4 }­Pt­(SH)] (90%, 0.01 mol %, 6 h, 65 °C) …”

“…The catalytic activity of complex 3 in the hydrosilylation of aldehydes is compared with the reported nickel pincer complexes to understand its efficiency. For example, benzyl alcohol formation from benzaldehyde is far better (98%, neat conditions, 25 °C, 2 h, Table 1, entry 14) compared to the precatalysts [( tBu PBP)NiH] (64%, 5 mol %, 9 h, 25 °C) reported by Rodri ́guez and coworkers 38 and [( tBu POCOP)-NiSH] (95%, 0.2 mol %, 18 h, 70 °C) reported by Chen and coworkers. 18 However, complex 3 performed less relative to the cyclopentadienyl bound nickel complex [(Cp*-NHC Me )-NiO t Bu] (89%, 1.0 mol %, 5 min, 25 °C) 39 and to the highly active nickel hydride [( iPr POCOP)NiH] reported by Guan and coworkers (79%, 0.2 mol %, 2 h, 25 °C).…”

“…37,38,40 The performance of complex 3 is greater than some of the reported complexes. For example, the secondary alcohol formation from acetophenone is much better (78%, 2.5 mol %, 8 h, 70 °C) than the activity of the reported complexes for the same product: [( iPr POCOP)NiH] (18%, 1.0 mol %, 24 h, 70 °C), 37 [( tBu PBP)NiH] (56%, 5.0 mol %, 6 h, 70 °C), 38 and [(Cp*-NHC Me )NiO t Bu] (77%, 2.0 mol %, 24 h, 100 °C). 39 However, complex 3 exhibits less activity than does the platinum thiolate complex [{B(NCH 2 P t Bu 2 ) 2 −1,2-C 6 H 4 }Pt(SH)] (90%, 0.01 mol %, 6 h, 65 °C).…”

Photoredox Synthesis of Silyl Ethers via Radical Coupling of Ketones with Hydrosilanes and [1, 2]‐Brook Rearrangement

“…Treatment of product 3 ba with tetrabutylammonium fluoride (TBAF) could afford the desilication product diphenylmethanol 4 in 95 % yield via the cleavage of silicon-oxygen bond (Scheme 4, 2a). [20] In addition, when silyl ether 3 ba was reacted with 1,3-dimethoxybenzene in the presence of AuCl 3 , Friedel-Crafts alkylation product 5 could be obtained in 81 % yield through the cleavage of carbon-oxygen bond (Scheme 4, 2b). [21] To glean further insights into the mechanism, control experiments and spectral analyses were performed.…”

Reactions of PNCNP and POCOP Pincer Platinum Hydride Complexes with Phenylacetylene and Carbon Disulfide: The Influence of the Pincer Backbone on the Structures of Unsaturated Auxiliary Ligands

“…Transition metal hydride complexes are of great importance in organometallic chemistry and catalysis . Particularly, those supported by pincer ligands have been extensively used as catalysts for various chemical transformations . Transition metal pincer complexes were first reported in the late 1970s .…”