L2Zn and LZnX complexes bearing half-salphen ligands and their catalysis of ring-opening polymerization of ε -caprolactone

Abstract

Zinc complexes L2Zn and LZnX were prepared by template synthesis from ZnX2, N1,N1-dimethylbenzene-1,2-diamine and substituted salicylaldehyde (SA). A systematic exploration of this synthetic route revealed the subtle role of choice of Zn source and SA substitution pattern on the reaction stoichiometry and enabled synthesis of pure Zn complexes. Use of poorly coordinating counterions (such as CF3SO3−) and apolar substituents on the SA component favours formation of pentacoordinate L2Zn, while more coordinating counterions tend to produce LZnX, (LZnX)2 or even binuclear LZn(O2CR)Zn(O2CR)2 not reported before. The complexes (LZnX)2 and LZn(O2CR)·Zn(O2CR)2 (L = L2 or L4) could be activated with BnOH/LiMe for ring-opening polymerization of ε-caprolactone; bis(ligand) complexes L2Zn show low or vanishing activity when activated either by BnOH or BnOH/LiMe.