The rational design and synthesis of efficient catalyst systems, which mediate the copolymerization of epoxides and carbon dioxide to form polycarbonates

The formation of cyclic propylene carbonate formed from the backbiting reaction of poly(propylene carbonate) onto zinc phenoxide catalysts has been monitored by infra-red spectroscopy. A zinc phenoxide complex with two cyclic propylene carbonate ligands occupying the open sites of the zinc catalyst center (Zn(O-2,6-tBu2C6H 3)2(propylene carbonate)2) has been synthesized and characterized by 13C NMR, elemental analysis, and X-ray crystallography. The cyclic propylene carbonate molecule is thought to be an inhibitor in this copolymerization reaction. The solid state characterization by X-ray crystallography of Zn(O-2,4,6-Me3C6H3 )2(pyridine)2 has also been accomplished. Additional 13C NMR studies with the zinc phenoxide complexes dissolved in pyridine-d 5 solvent have shown that CO2 insertion into the Zn-O bond is a facile process when the oxygen lone pair of electrons are not sterically blocked.;The synthesis of a novel three-coordinate zinc phenoxide phosphine complex (Zn(O-2,6-tBu2(C6H3) 2(PCy3)) was accomplished and characterized by 31 P NMR, 13C NMR, elemental analysis, and X-ray crystallography. This complex was shown in previous work to be active in the copolymerization of cyclohexene oxide and CO2 while limiting the formation of polyether linkages within the copolymer backbone. A series of cadmium phenoxide phosphine complexes with one or two phosphine ligands was synthesized and characterized by 31P NMR, 113Cd NMR, 13C NMR, and elemental analysis. Data obtained from 31P NMR and 113Cd NMR of these complexes have given insight into the solution behavior of their zinc analogs. The complexes Cd(O-2,6-tBu 2C6H3)2(PCy3) and Cd(O-2,6- tBu2C6H3)2(PMe3) 2 were also characterized by X-ray crystallography. The solid state structures of the cadmium complexes were similar to their zinc analogs.;A series of salicylaldimine ligands was synthesized and reacted with ½ equivalent of Zn[N(SiMe3)2]2 in THF or pentane to form zinc bis(salicylaldiminato) complexes. These complexes were characterized by 1H NMR, 13C NMR, elemental analysis, and X-ray crystallography. The bis salicylaldiminato zinc complexes are active in the copolymerization of cyclohexene oxide and CO2. The activity is dependent on the steric and electronic effects of the ligands. The formation of cyclic propylene carbonate suggests that these complexes do not prevent the backbiting reaction in the copolymerization of propylene oxide and CO2.