Carbosilylation of alkenes can be an efficient approach to the synthesis of organosilicon compounds. However, few general methods of carbosilylation are known. Here, we introduce a strategy for arylsilylation of electron-deficient terminal alkenes by combining photoredox-catalyzed silyl radical generation, innate reactivity of silyl radical with alkene, and Ni-catalyzed aryl-alkyl cross-coupling. This cooperative photoredox and nickel catalysis operates under mild conditions. It employs readily available alkenes, aryl bromides, and silane as reagents, and it produces useful synthetic building blocks in a modular manner.

Conspectus Ligand development plays an essential role in the advance of homogeneous catalysis. Tridentate, meridionally coordinating ligands, commonly termed pincer ligands, have been established as a privileged class of ligands in catalysis because they confer high stability while maintaining electronic tenability to the resulting metal complexes. Pincer ligands containing “soft” donors such as phosphines are typically used for late transition-metal ions, which are considered “soft” acids. Driven by our interest to develop base-metal catalysis and in view of the “hard” character of base-metal ions, our group explored a pincer ligand containing only “hard” nitrogen donors. A prototypical nickel complex of this ligand, “Nickamine”, turned out to be an efficient catalyst in a wide range of organic reactions. Because of its propensity to mediate single-electron redox chemistry, Nickamine is particularly suited to catalyze cross-coupling of nonactivated alkyl halides through radical pathways. These coupling partners have been challenging substrates for traditional, palladium-based catalysts because of difficult oxidative addition and nonproductive β-H elimination. The high activity of Nickamine for cross-coupling leads to high chemoselectivity and functional group tolerance, even when reactive Grignard reagents are employed as nucleophiles. The scope of the catalysis is broad and encompasses sp3–sp3, sp3–sp2, and sp3–sp cross-coupling. The defined nature of Nickamine facilitated the mechanistic study of cross-coupling reactions. Experiments involving radical-probe substrates, presumed intermediates and dormant species, kinetics, and density functional theory computations revealed a bimetallic oxidative addition pathway. In this pathway, two Ni centers each provide one electron to support the two-electron activation of an alkyl halide substrate. The success of Nickamine motivated our systematic structure–activity studies aiming at improved activity in certain reactions through ligand modification. Indeed, better catalysts have been developed for cross-coupling of secondary alkyl halides as well as direct alkynylation of alkyl halides. The improvement is attributed to a more accessible Ni center in the new catalysts than in Nickamine. Surprisingly, the improvement could be obtained simply by replacing a dimethyl amino group in Nickamine with a pyrrolidino group. During the study of the catalytic cycle of Nickamine in cross-coupling reactions, we synthesized the corresponding Ni–H species. Consequently, we explored the catalytic application of Nickamine in Ni–H mediated reactions, such as hydrosilylation. To our delight, Nickamine is a chemoselective catalyst for hydrosilylation of alkenes while tolerating a reactive C=O group. An analogous Ni pincer complex was found to catalyze unusual hydrosilylation reactions using alkoxy hydrosilanes as surrogates of gaseous silanes.

Deracemization of racemic chiral compounds is an attractive approach in asymmetric synthesis,b ut its development has been hindered by energetic and kinetic challenges. Here we describe ac atalytic deracemization method for secondary benzylic alcohols which are important synthetic intermediates and end products for many industries.Driven by visible light only,t his method is based on sequential photochemical dehydrogenation followed by enantioselective thermal hydrogenation. The combination of ah eterogeneous dehydrogenation photocatalyst and ac hiral molecular hydrogenation catalyst is essential to ensure two distinct pathwaysfor the forwarda nd reverse reactions.T hese reactions convert al arge number of racemic aryl alkyla lcohols into their enantiomerically enriched forms in good yields and enantioselectivities.

Easily-assembled Ni MOFs are efficient and robust catalysts for alkene hydrosilylation.