Bimetallic Anilido-Aldimine Zinc Complexes for Epoxide/CO2 Copolymerization

Acyclic o-phenylene-bridged bis (anilido-aldimine) compounds, o-C (6) H (4) C (6) H (2) R (2) N=CH-C (6) H (4) - (H) N (C (6) H (3) R' (2) ) (2) and related 30-membered macrocyclic compounds, o-C (6) H (4) C (6) H (2) R' (2) N=CH-C (6) H (4) - (H) N-C (6) H (2) R (2) (2) (o-C (6) H (4) ) are prepared. Successive additions of Me (2) Zn and SO (2) gas to the bis (anilido-aldimine) compounds afford quantitatively dinuclear mu-methylsulfinato zinc complexes, o-C (6) H (4) (C (6) H (2) R (2) N=CH-C (6) H (4) -N (C (6) H (3) R' (2) ) -kappa (2) -N, N) Zn (mu-OS (O) Me) (2) (R = iPr and R' = iPr, 29; R = Et and R' = Et, 30; R = Me and R'= Me, 31; R = Me and R' = iPr, 32; R = Et and R' = Me, 33; R = Et and R' = iPr, 34; R = iPr and R' = Et, 35) and o-C (6) H (4) C (6) H (2) R' (2) N=CH-C (6) H (4) -N-C (6) H (2) R (2) -kappa (2) -N, N) Zn (mu-OS (O) Me) (2) (o-C (6) H (4) ) (R = Et and R'= Et, 36; R = Me and R' = Me, 37; R = iPr and R' = Me, 38; R = Et and R' = Me, 39; R = Me and R'= iPr, 40). Molecular structures of 34 and 40 are confirmed by X-ray crystallography. Complexes 30-35 show high activity for cyclohexene oxide/CO (2) copolymerization at low Zn/monomer ratio (1: 5600), whereas the complex of mononucleating beta-diketiminate (C (6) H (3) Et (2) ) N=C (Me) CH=C (Me) N (C (6) H (3) Et (2) ) Zn (mu-OS (O) Et) (2) shows negligible activity in the same condition. Activity is sensitive to the N-aryl ortho substituents and the highest activity is observed with 32. Turnover number up to 2980 and molecular weight (M (n) ) up to 284 000 are attained with 32 at such a highly diluted condition as Zn/monomer = 1: 17 400. Macrocyclic complexes 36-40 show negligible activity for copolymerization.