Trivalent Titanium Salen Complex: Thermally Robust and Highly Active Catalyst for Copolymerization of CO₂ and Cyclohexene Oxide

Abstract

A trivalent titanium complex combining salen ligand (salen-H2═N,N-bis(3,5-di-tert-butylsalicylidene)-1,2-benzenediamine) was synthesized as catalyst for copolymerization of CO2 and cyclohexene (CHO). In combination with onium salt [PPN]Cl, (Salen)Ti(III)Cl showed impressive activity and selectivity, yielding completely alternating copolymer without the formation of cyclohexene carbonate (CHC), with turnover frequency (TOF) of 557 h–1 at 120 °C, which was more than 10 times higher than that of our previously reported (Salalen)Ti(IV)Cl, and close to the Cr counterparts. In addition to the biocompatibility of Ti, thermally robust character resulting from the reducibility of trivalent Ti was industrially desirable.