Bimetallic anilido-aldimine zinc complexes for epoxide/CO2 copolymerization

Acyclic o-phenylene-bridged bis(anilido-aldimine) compounds, o-C6H4{C6H2R2N=CH-C6H4(H)N(C6H3R'(2))}(2) and related 30-membered macrocyclic compounds, o-C6H4{C6H2R'N-2=CH-C6H4-(H)-N(C6H2R2}(2) (o-C6H4) are prepared. Successive additions of Me2Zn and SO2 gas to the bis(anilido-aidimine) compounds afford quantitatively dinuclear mu-methylsulfinato zinc complexes, o-C6H4{(C6H2R2N=CH-C6H4N(C6H3R'(2))-kappa(2)-N,N)Zn(mu-OS(O)Me)(2) (R = iPr and R' = Pr, 29; R = Et and R' = Et, 30; R = Me and R' = Me, 31; R = Me and R' = Pr, 32; R = Et and R' = Me, 33; R = Et and R' = Pr, 34; R = Pr and R' = Et, 35) and o-C6H4{C6H2R'N-2=CH-C6H4-N-C6H2R2-kappa(2)-N,N)Zn(mu-OS(O)Me)}(2) (o-C6H4) (R Et and R' = Et, 36; R = Me and R' = Me, 37; R = Pr and R' = Me, 38; R = Et and R' = Me, 39; R Me and R' = Pr, 40). Molecular structures of 34 and 40 are confirmed by X-ray crystallography. Complexes 30-35 show high activity for cyclohexene oxide/CO2 copolymerization at low [Zn]/[monomer] ratio (1:5600), whereas the complex of mononucleating beta-diketiminate {[(C6H3Et2)N=C(Me)CH=C(Me)N(C6H3Et2)]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.