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)H][BF4-], 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.