Pd-phosphite and Pd-Pd tetrazolyl paddlewheel complexes as catalysts for CO2 hydrogenation

Abstract

Hydrogenation of CO2 to products such as formic acid has gained attention in recent times as one of the means of addressing the environmental impact of CO2 as well as H2 storage. Herein we report the synthesis of a tetrazolyl ligands bearing PS bonds which undergoes a PS heterolysis during complexation with [PdCl2(MeCN)2] resulting in the accidental synthesis of palladium-tetrazolyl paddlewheel complexes and corresponding palladium phosphite complexes with P-OH bonds. This PS heterolysis depends on the nature of substituents present on the phosphorus atom present in the ligand since P^N bidentate coordination is possible. These palladium complexes were then evaluated as precatalysts for CO2 hydrogenation where TONs of around 564 were observed. Presence of proton responsive P-OH groups contribute towards catalytic activity as a result of an assisted H2 heterolysis. A plausible mechanism of action indicates bicarbonate coordinates to Pd followed by elimination of water which subsequently results in the generation of formate.