Single-Site β-Diiminate Zinc Catalysts for the Alternating Copolymerization of CO<sub>2</sub> and Epoxides:  Catalyst Synthesis and Unprecedented Polymerization Activity
                                
                                    
                                        作者:Ming Cheng、David R. Moore、Joseph J. Reczek、Bradley M. Chamberlain、Emil B. Lobkovsky、Geoffrey W. Coates                                    
                                    
                                        DOI:10.1021/ja003850n
                                    
                                    
                                        日期:2001.9.1
                                    
                                    Synthetic routes to zinc ss -diiminate complexes are reported. The synthesis of 11 ss -diimine [(BDI)H] ligands, with varying N-aryl substituents and bridging structures, is described. These ligands are converted to (BDI)ZnX complexes (X = OAc. Et. N(SiMe3)(2), Br, Cl, OH, OMe, (OPr)-Pr-i). X-ray structural data revealed that all zinc complexes examined exist as mu -X-bridged dimers in the solid state, with the exception of the zinc ethyl and amido complexes which were monomeric. Complexes of the form (BDI)ZnOR (R = alkyl, acyl) and (BDI)ZnN(SiMe3)(2) are highly active catalysts for the alternating copolymerization of epoxides and CO2. Copolymerizations of cyclohexene oxide (CHO) and CO2 with (BDI-1)ZnX [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)imino)-2-pentene)] and (BDI-2)ZnX [(BDI-2) = 2-((2,6-diethylphenyl)amido)-4-((2,6-diethylphenyl)imino)-2-pentene)], where X = OAc, Et, N(SiMe3)(2), Br, Cl, OH, OMe, (OPr)-Pr-i, were attempted at 50 degreesC and 100 Psi CO2. Complexes with X = OAc, N(SiMe3)(2), OMe, (OPr)-Pr-i all produced polycarbonate by the alternated insertion of CHO and CO2 with similar catalytic activities, comparable molecular weights, and narrow molecular weight distributions (MWD similar to 1.1), indicating the copolymerizations are living. Furthermore, ligand effects were shown to dramatically influence the polymerization activity as minor steric changes accelerated or terminated the polymerization activity.