Exhaustive reduction of aromatic esters and carboxylic acids with a homogeneous cobalt catalyst

A one-step procedure to exhaustively reduce aromatic esters and carboxylic acids to their corresponding tolyl derivatives is a significant transformation in organic synthesis, which remains challenging in homogeneous catalysis. In this study, it's achieved by using the well-defined phosphinesulfonate chelated cobalt-based catalyst (Co(dppbsa)), along with NaBAr^F₄ as the basic additive and (MeO)₂MeSiH as the reductant. Particularly, this cobalt catalysis proceeds through ether intermediates. Experimental combined theoretical results support it follows an outer-sphere ionic hydrosilylation mechanism and the in situ formed cationic siloxane species are involved in the rate-limiting hydride transfer. The same system also enables the catalytic deoxygenation of aliphatic esters, aliphatic acids, and amides but terminating at the corresponding ethers, alkanols and secondary amines, respectively. These findings open up novel avenues for the catalytic application of phosphinesulfonate chelated complexes, potentially serving as the foundation for the exhaustive reduction of carboxylic skeletons with cobalt.