Indium-Catalyzed CO2/Epoxide Copolymerization: Enhancing Reactivity with a Hemilabile Phosphine Donor.

Group 13 metal complexes have emerged as powerful catalysts for transforming CO2 into added-value products. However, direct comparisons of reactivity between Al, Ga, and In catalysts are rare. We report aluminum (1), gallium (2), and indium (3) complexes supported by a half-salen H[PNNO] ligand with a pendent phosphine donor and investigate their activity as catalysts for the copolymerization of CO2 and cyclohexene oxide. In solution, the P-donor is dissociated for the Al and Ga complexes while for the In complex it exhibits hemilabile behavior. The indium complex shows higher conversion and selectivity than the Al or Ga analogues. The mechanism of the reaction was studied by NMR and FTIR spectroscopy experiments as well as structural characterization of off-cycle catalytic intermediate indium trichloride complex [(PNNO)InCl3][TBA] (4). This study highlights the impact of a hemilabile phosphine group on group 13 metals and provides a detailed analysis of the initiation step in CO2/epoxide copolymerization reactions.