Syntheses of Cationic Bis(Phosphine) Cobalt (III) and (I) Precatalysts and Performance in Alkene and Alkyne Hydrofunctionalization Reactions

Abstract

The functionalization of hydrocarbon feedstocks has applications in the fine chemicals, fuels, pharmaceutical, and flavor and fragrance industries. Two such hydrofunctionalization reactions, hydrosilylation and hydroboration reactions, are typically catalyzed by precious metal catalysts, such as Platinum, Ruthenium, Iridium, and Rhodium, which are expensive and not environmentally sustainable. As a result, motivation exists for the development of Earth-Abundant metal catalysts, such as Cobalt catalysts, as these catalysts are cheaper, more environmentally sustainable, and can promote the same or new hydrofunctionalization reactions with similar or higher activity. Previous research has shown an active Bis(Phosphine) Co(I) catalyst in these hydrofunctionalization reactions, but very little work has been done into the isolation and characterization of these complexes. In this work, I focused on the versatile synthesis of bench-stable Bis(Phosphine) Co(III) and Co(I) complexes, including activation of these complexes toward hydrosilylation and hydroboration. Using NMR spectroscopy I characterized seven viable Bis(Phosphine) Co(III) and Co(I) precatalysts, and further characterized four of these precatalysts by solid state X-Ray Crystallography. The successful hydrosilylation reactions with aliphatic alkenes resulted exclusively anti-Markovnikov product formation, while hydrosilylation with vinyl arenes resulted in a ratio of anti-Markovnikov to Markovnikov products. Hydroboration resulted in anti-Markovnikov products exclusively, and hydroboration of dienes resulted in a ratio of regioisomers that varied dependent upon the ligand used in the precatalyst.