Abstract
AbstractAlkene hydrosilylation is amongst the largest industrial homogenous catalysis processes. Cobalt catalysis offers a sustainable alternative to commonly used platinum catalysts to achieve this transformation. Using two bisiminopyridine cobalt(II) catalysts the regiodivergent hydrosilylation of alkenes has been developed. Variation of pre‐catalyst activator and ligand substituents were investigated to enable the controlled, regiodivergent hydrosilylation of both aryl‐ and alkyl‐substituted alkenes with phenylsilane. In contrast to other regiodivergence strategies, excellent regioselectivity for either isomer was achieved using the same ligand class but differing by a single methyl group (ethyl vs isopropyl).
Highlights
Alkene hydrosilylation is one of the largest industrial applications of homogenous catalysis and enables fields as diverse as soft plastics and anti-foaming agents.[1,2] The most commonly used hydrosilylation catalysts remain platinum-based, with Speier’s and Karstedt’s complexes being key examples.[3,4] The high activity and ease of use of these platinum complexes have given these catalysts ubiquity over other transition-metal alternatives and outweighs the scarcity, volatile cost and sourcing of platinum
During the course of preliminary investigations into pre-catalyst activation using alkoxide salts, and akin to the report of Rajanbabu,[20] it was discovered that cobalt complexes containing the bisiminopyridine ligand framework (BIP) would give mixtures of linear and branched alkylsilane products in alkene hydrosilylation with improved selectivity over previous methods
A series of cobalt(II) bis(imino) pyridine ligands (BIP) complexes with differing steric environments were investigated (Table 1)
Summary
Alkene hydrosilylation is one of the largest industrial applications of homogenous catalysis and enables fields as diverse as soft plastics and anti-foaming agents.[1,2] The most commonly used hydrosilylation catalysts remain platinum-based, with Speier’s and Karstedt’s complexes being key examples.[3,4] The high activity and ease of use of these platinum complexes have given these catalysts ubiquity over other transition-metal alternatives and outweighs the scarcity, volatile cost and sourcing of platinum. During the course of preliminary investigations into pre-catalyst activation using alkoxide salts, and akin to the report of Rajanbabu,[20] it was discovered that cobalt complexes containing the bisiminopyridine ligand framework (BIP) would give mixtures of linear and branched alkylsilane products in alkene hydrosilylation with improved selectivity over previous methods. The most sterically hindered complex, iPrBIPCoCl2, which following the observed trend would have been expected to give improved Markovnikov selectivity, instead showed excellent selectivity for the antiMarkovnikov regioisomer to give the linear alkylsilane 3 a in high yield (Table 1, entry 4).
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