Unusually Stable Chiral Ethyl Zinc Complexes: Reactivity and Polymerization of Lactide

Chiral diaminophenoxy proligands, H(NN R′ O R ), where R = t -Bu, H and R′ = Me, H, have been developed and their respective zinc ethyl complexes, (NN R′ O R )ZnEt, 3a (R = t -Bu, R′ = Me), 3b (R = H, R′ = Me), 3c (R = t -Bu, R′ = H), have been synthesized. The reactivity of 3a with alcohols was explored in detail and compared to a compound reported by Hillmyer, Tolman et al., LZnEt ( L = 2,4-di- tert -butyl-6-{[(2′-dimethylaminoethyl)methylamino]-methyl}phenolate). Unlike LZnEt, 3a was inert toward ethanol (as well as methanol, isopropanol, and water). It reacted with phenol and with hydrochloric acid to form (NN Me O tBu )ZnOPh, 4a, and (NN Me O tBu )ZnCl, 5a, respectively. Racemic and enantiopure forms of 4a, (±) -4a and ( R,R )- 4a, were synthesized. The phenoxide complex catalyzed the ring opening polymerization of lactide to atactic poly(lactic acid).