Mechanism of the Pyridine-Modified Cobalt-Catalyzed Hydromethoxycarbonylation of 1,3-Butadiene

The pyridine-modified cobalt-catalyzed hydromethoxycarbonylation of 1,3-butadiene (1) starts by the disproportionation of Co2(CO)8 to [CoPy6][Co(CO)4]2 followed by the formation of HCo(CO)4 (3). The addition of 3 to 1 leads to CH3CHCHCH2Co(CO)4 (4), which, depending on the conditions, can undergo facile CO insertion to yield CH3CHCHCH2COCo(CO)4 (5) or reversible decarbonylation to form η3-C4H7Co(CO)3 (7). Pyridine accelerates the conversion of 7 to methyl-3-pentenoate (2) and the methanolysis of 5.