A stable acyl cobalt-based catalyst with exceptionally elevated activity for the carbonylation of epoxides into β-lactones

ABSTRACT

Polyhydroxyalkanoate (PHA), a well-known biodegradable polymer, features β-lactones as its monomers, which can be selectively synthesized through ring-expansion carbonylation of epoxides using well-defined [Lewis acid]⁺[Co(CO)₄]^– catalysts. However, the decomposition of [Co(CO)₄]^– species at temperatures exceeding 80 °C presents a hurdle for the development of commercially viable processes under high-temperature reaction conditions to reduce reaction time. Drawing insights from stable {(acyl)Co(CO)_n} intermediates involved in historical HCo(CO)₄-catalyzed hydroformylation processes, we sought to the high-temperature catalytic activity of epoxide ring-expansion carbonylation. The developed catalyst system, [(acetyl)Co(CO)₂dppp] and [(TPP)CrCl], exhibited exceptional catalytic performance with an unprecedented initial turnover frequency of 4700 h^–1 at 100 °C and a turnover numbers of 93000. Notably, the catalyst displayed outstanding stability, operating at 80 °C for 168 h while selectively generating β-lactones.