Bimetallic fluorine-substituted anilido-aldimine zinc complexes for CO2/(cyclohexene oxide) copolymerization

Regioselective nucleophilic aromatic substitution of an o-fluorine occurs to afford fluorine-substituted o-phenylene-bridged bis(anilido-aldimine) compounds o-C6H4{(C6H2R2)N=CH-C6F4-( H) N(C6H3R'(2))}(2) when Li(H) N-C6H3R2 (R)' = iPr, Et, Me) is reacted with o-C6H4 {(C6H2R2) N = CH -C6F5}(2) (R) iPr, Et, Me) in a nonpolar solvent such as diethyl ether or toluene. Successive additions of Me2Zn and SO2 gas to the bis(anilido-aldimine) compounds afford quantitatively dinuclear mu-methylsulfinato zinc complexes o- C6H4 {[( C6H2R2) N = CH - C6F4 - N(C6H3R2)-k(2)N,N]Zn(mu-OS(O)Me)}(2) ( R= iPr, R ' = iPr, 3a; R = iPr, R ' = Me, 3c; R) Et, R) i Pr, 3d; R) Et, R) Et, 3e; R) Et, R) Me, 3f; R) Me, R) i Pr, 3g; R = Me, R ' = Et, 3h; R = Me, R = Me, 3i). The molecular structure of 3c was confirmed by X- ray crystallography. Fluorine- substituted complexes 3a-i show significantly higher TOF (turnover frequencies) than the unfluorinated analogues for CO2/(cyclohexene oxide) copolymerization. The TOF is highly sensitive to the substituents R and R, and the highest TOF (2480 h(-1)) is obtained with 3g ( R = Me, R ' iPr). Complex 3g is less sensitive to the residual protic impurities present in the monomers and shows activity at such a low catalyst concentration as [Zn]:[cyclohexene oxide]) 1:50 000, at which the unfluorinated analogue is completely inactive. By realizing the activity at such an extremely low [Zn]:[cyclohexene oxide]ratio, we achieve a high TON (turnover number) up to 10 100. High-molecular-weight polymers (M (n), 100 000-200 000) are obtained with a rather broad molecular-weight distribution (M-w/M-n, 1.3-2.5). The obtained polymers are not perfectly alternating, and variable carbonate linkages (65 -85%) are observed depending on the N-aryl ortho substituents R and R and the polymerization conditions.