Synthesis and Application of Bench-Stable Cobalt Catalysts toward Parahydrogen-Induced Polarization

The widespread application of first-row transition metal catalysts for parahydrogen-induced polarization (PHIP) is hindered by their air sensitivity and subsequent need for highly reactive, pyrophoric reductants to produce the active catalyst. Herein, we report a bench-stable cobalt(III) bis(acetate) precatalyst, (MesCCC)Co(OAc)2 (MesCCC = bis(2,4,6-trimethylphenylbenzimidazol-2-ylidene)phenyl), that overcomes these limitations. This complex undergoes clean in situ reduction to an active cobalt(I) species using mild tertiary silanes and heat, proceeding via proposed sequential σ-complex-assisted metathesis (σ-CAM) steps. The in situ-generated catalyst successfully mediates styrene hydrogenation with p-H2, demonstrating both hyperpolarization of the alkene and alkane. Ultimately, this robust, easily activated precursor provides a highly accessible platform for base-metal PHIP catalysis, simplifying experimental protocols and substrate expansion.