Zirconium-Catalysed Hydrosilylation of Esters and Depolymerisation of Polyester Plastic Waste

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, with 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 sigma bond metathesis of Zr–O and 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 alcohol (up to 91% isolated yield). We have also applied this methodology to the reductive depolymerisation of polyesters found in household plastic waste.