Single-Site β-Diiminate Zinc Catalysts for the Alternating Copolymerization of CO2 and Epoxides: Catalyst Synthesis and Unprecedented Polymerization Activity

Top Cited Papers
Publisher Website
Google Scholar
Abstract
Synthetic routes to zinc β-diiminate complexes are reported. The synthesis of 11 β-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, OiPr). X-ray structural data revealed that all zinc complexes examined exist as μ-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, OiPr, were attempted at 50 °C and 100 psi CO2. Complexes with X = OAc, N(SiMe3)2, OMe, OiPr all produced polycarbonate by the alternated insertion of CHO and CO2 with similar catalytic activities, comparable molecular weights, and narrow molecular weight distributions (MWD ∼ 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.

This publication has 37 references indexed in Scilit: