Mechanistic Study of Alkene Hydrosilylation Catalyzed by a β-Dialdiminate Cobalt(I) Complex

Abstract

Alkene hydrosilylation is a large-scale process that typically uses precious-metal catalysts. A new generation of highly selective catalysts is based on inexpensive metals, which may have a high-spin electronic configuration and thus may follow novel mechanistic pathways. Here, we describe mechanistic studies on a high-spin cobalt(I) catalyst that performs rapid and regioselective alkene hydrosilylation. Using 1-hexene and PhSiH 3 as substrates, we elucidate features of the rate law, test for free radical intermediates with radical clock substrates, and use deuterium substitution to provide mechanistic insight. The resting state has PhSiH 3 bound η 6 through the phenyl group and evolves over the course of the reaction from a substrate-bound form to a product-bound form. This complicates analysis by variable time normalization analysis (VTNA) because the dependence of the rate on [PhSiH 3 ] is not constant throughout the reaction. Despite this challenge, the accumulated results are consistent with initial oxidative addition of PhSiH 3 , followed by alkene binding, and then insertion through the Chalk−Harrod or modified Chalk− Harrod mechanism to form the hydrosilylation product. Though the catalyst has a paramagnetic metal center, none of the data implicate radicals participating in the mechanism, and a conventional electron-pair mechanism is most consistent.

(NHC)Ni(0)-Catalyzed Branched-Selective Alkene Hydrosilylation with Secondary and Tertiary Silanes

“…Catalysts composed of base metals ,− like Ni, − Mn, − Co, − and Fe ,− have been developed for linear-selective alkene hydrosilylation. As a congener of Pt, Ni is especially promising as a base-metal candidate for alkene hydrosilylation.…”

Cobalt‐Catalysed, Ligand‐Controlled Regiodivergent Alkene Hydrosilylation

“…Although many first‐row metal catalysts have been used for hydrosilylation, mechanistic understanding for many of these systems remains elusive [9f] . Studies of cobalt‐catalysed hydrosilylation reactions using cobalt‐carbonyl [24] and cyclopentadienyl‐cobalt complexes [25] suggested a prevelance of a modified Chalk‐Harrod mechanism of alkene silyl‐metallation followed by carbon‐hydrogen bond forming reductive elimination [26] .…”

The synthesis of heterogenous Co‐MOFs and application in the catalytic hydrosilylation of alkenes

“…Based on the experiments and literatures, [33,34] a proposed mechanism was showed in Scheme 2. First, the cobalt catalyst precursor reacts with silane and NaBEt 3 H to provide low-valent [Co] + silyl species I; second, the species I then inserted into alkenes to generate cobalt alkyl intermediate II and forms to intermediates III; in the third step, the species III react with the silane to form the hydrosilylation adduct and the cobalt catalyst enter into the next catalytic cycle.…”