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 Co 2 (CO) 8 to [CoPy 6 ][Co(CO) 4 ] 2 followed by the formation of HCo(CO) 4 ( 3 ). The addition of 3 to 1 leads to CH 3 CH CHCH 2 Co(CO) 4 ( 4 ), which, depending on the conditions, can undergo facile CO insertion to yield CH 3 CH CHCH 2 COCo(CO) 4 ( 5 ) or reversible decarbonylation to form η 3 -C 4 H 7 Co(CO) 3 ( 7 ). Pyridine accelerates the conversion of 7 to methyl-3-pentenoate ( 2 ) and the methanolysis of 5 .