Zirconium-catalysed hydrosilylation of esters and depolymerisation of polyester plastic waste

Abstract

Schwartz's reagent, Cp2Zr(H)Cl, has traditionally been used as a stoichiometric reagent for the reduction of unsaturated organic molecules. Recently, methods to use Cp2Zr(H)Cl as a catalyst have been developed through turnover of the [Zr]-X intermediates, formed upon reaction with an organic substrate, by hydride reagents. Herein, we report the development of a new catalytic pathway for the reduction of esters that uses the bench-stable silane Me(OMe)2SiH (DMMS) as a mild stoichiometric reductant and Cp2Zr(H)Cl as the catalyst. This system exploits the regeneration of [Zr]-H through the σ-bond metathesis of [Zr]-OR with [Si]-H to achieve catalyst turnover. These reaction conditions tolerate a range of reducible functional groups (e.g. alkyne, alkene, and nitro) and give high yields of the corresponding alcohols (up to 91% isolated yield). This methodology also proved fruitful for the reductive depolymerisation of a variety of polyesters found in household plastic waste.