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‘2NCH−C6H4−(H)N−C6H2R2}2 (o-C6H4) are prepared. Successive additions of Me2Zn and SO2 gas to the bis(anilido-aldimine) compounds afford quantitatively dinuclear μ-methylsulfinato zinc complexes, o-C6H4{(C6H2R2NCH−C6H4−N(C6H3R‘2)-κ2-N,N)Zn(μ-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-C6H4{C6H2R‘2NCH−C6H4−N−C6H2R2-κ2-N,N)Zn(μ-OS(O)Me)}2 (o-C6H4) (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/CO2 copolymerization at low [Zn]/[monomer] ratio (1:5600), whereas the complex of mononucleating β-diketiminate {[(C6H3Et2)NC(Me)CHC(Me)N(C6H3Et2)]Zn(μ-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 (Mn) 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.