Titanium-mediated coupling of CO2 and ethylene to acrylate: mechanistic insights from Cp*2Ti complexes

Abstract

The coupling of CO₂ and ethylene to acrylate is a promising route for CO₂ utilization, yet known catalytic systems are limited by low activity and harsh reaction conditions. These limitations are closely linked to the difficulty of metallalactone intermediate formation in late transition metal systems. Here, we investigate titanium-mediated coupling of CO₂ and ethylene to acrylate using Cp*₂Ti complexes and elucidate the elementary steps that enable acrylate formation under mild conditions. The oxophilic titanium promotes CO₂/ethylene coupling with a low activation barrier, and the resulting Ti(IV) metallalactone is thermodynamically stabilized by strong Ti–O interactions. Subsequent conversion to acrylate is readily achieved through deprotonation by an alkoxide base, while the canonical β-hydride elimination pathway remains unfavorable. Despite the kinetic accessibility of acrylate formation, mechanistic studies reveal that catalytic turnover is limited by competing Ti(II)/Ti(IV) comproportionation. These findings outline the operative steps and current limitations of titanium-mediated acrylate synthesis and provide a basis for the design of early transition metal catalysts for carboxylation chemistry.