Benzannulated N-heterocyclic plumbylene: An efficient catalyst in ring opening polymerization of l-lactide

Abstract

Main-group metal-based catalysts have attracted considerable attentions due to their complementary reactivities to transition metals. In searching for the catalytic application of heavy divalent Group 14 derivatives, we came to discover that the benzannulated N-heterocyclic plumbylene (1) could serve as an effective catalyst for ring-opening polymerization of l-lactide (L-LA) at room temperature. In the presence of benzyl alcohol (BnOH), 97% conversion of L-LA was accomplished in 10 min under a catalyst loading of merely 0.3 mol% ([LA]:[1]:[BnOH] = 400:1.2:1.2, [1] = 1.2 mM). Compared to the polymeric plumbylene ([Pb(μ-OiPr)2]∞), the excellent catalytic activity of 1 at ambient temperature may be ascribed to the steric and electronic stabilizations of the Pb2+ center by the organic backbone. Thus, thermal activation is no longer required to expose the Lewis acidic metal center for polymerization.