Single-site beta-diiminate zinc catalysts for the alternating copolymerization of CO2 and epoxides: Catalyst synthesis and unprecedented polymerization activity

Synthetic routes to zinc ss -diiminate complexes are reported. The synthesi s 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 st ructural data revealed that all zinc complexes examined exist as mu -X-brid ged dimers in the solid state, with the exception of the zinc ethyl and ami do complexes which were monomeric. Complexes of the form (BDI)ZnOR (R = alk yl, acyl) and (BDI)ZnN(SiMe3)(2) are highly active catalysts for the altern ating copolymerization of epoxides and CO2. Copolymerizations of cyclohexen e 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)], w here 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 n arrow molecular weight distributions (MWD similar to 1.1), indicating the c opolymerizations are living. Furthermore, ligand effects were shown to dram atically influence the polymerization activity as minor steric changes acce lerated or terminated the polymerization activity.