Cooperative Initiation in a Dinuclear Indium Complex for CO2 Epoxide Copolymerization

Dinuclear indium complexes have been synthesized and characterized. These include neutral and cationic indium complexes supported by a Schiff base ligand bearing a binaphthol linker. The new compounds were investigated for alternating copolymerization of CO2 and cyclohexene oxide. In particular, the neutral indium chloride complex (+/-)-[(ONapNiN)InCl2]2 (4) showed high conversion of cyclohexene oxide and selectivity for poly(cyclohexene carbonate) formation without cocatalysts at 80 degrees C under various CO2 pressures (2-30 bar). Importantly, the reactivity of the dinuclear indium chloride complex 4 is drastically different from that of the mononuclear indium chloride complex (+/-)-(NNiOtBu)InCl2 (5), suggesting a cooperative initiation mechanism involving the two indium centers in 4.