Two Components in a Molecule:  Highly Efficient and Thermally Robust Catalytic System for CO2/Epoxide Copolymerization

Salicylaldehyde compound containing an ammonium salt unit, 2- (HO) -3-tBu-5-Bu3N+ (CH2) 3Si (Me2) C6H2C (O) HBF4-, is prepared from which a Salen-type ligand and its cobalt (III) complex, (Salen-1) CoX (1: Salen-1 = trans-N, N‘-bis (3-tBu-5- (Bu3N+ (CH2) 3Si (Me2) -salicylidene) -1, 2-cyclohexanediamine) X2; X = 2, 4-dinitrophenolate), is prepared. Complex 1 shows high activity for CO2/ (propylene oxide) copolymerization even at a condition of high propylene oxide/catalyst ratio and high temperature up to 90 °C, at which conditions a typical binary system of (Salen) CoX/PPNCl does not yield any copolymer. A very high TOF (up to 3500 h-1) and TON (up to 14500) are achieved, which have never been attained with other catalytic systems. The high selectivity (>84%) for the formation of copolymer over cyclic carbonate and the high molecular weight of the obtained polymers (Mn = 53000−95000) are the other merits of the catalyst.