A Single Bioinspired Hexameric Nickel Catechol-Alloxazine Catalyst Combines Metal and Radical Mechanisms for Alkene Hydrosilylation.
Agnideep DasJules SchleinitzLydia KarmazinBruno VincentNolwenn Le BretonGuillaume RogezAurélie GuenetSylvie ChouaLaurence GrimaudMarine Desage-El MurrPublished in: Chemistry (Weinheim an der Bergstrasse, Germany) (2022)
Mechanisms combining organic radicals and metallic intermediates hold strong potential in homogeneous catalysis. Such activation modes require careful optimization of two interconnected processes: one for the generation of radicals and one for their productive integration towards the final product. We report that a bioinspired polymetallic nickel complex can combine ligand- and metal-centered reactivities to perform fast hydrosilylation of alkenes under mild conditions through an unusual dual radical- and metal-based mechanism. This earth-abundant polymetallic complex incorporating a catechol-alloxazine motif as redox-active ligand operates at low catalyst loading (0.25 mol%) and generates silyl radicals and a nickel-hydride intermediate through a hydrogen atom transfer (HAT) step. Evidence of an isomerization sequence enabling terminal hydrosilylation of internal alkenes points towards the involvement of the nickel-hydride species in chain walking. This single catalyst promotes a hybrid pathway by combining synergistically ligand and metal participation in both inner- and outer- sphere processes.