First example of a gold(I) N-heterocyclic-carbene-based initiator for the bulk ring-opening polymerization of L-lactide

Synthesis, structure, and catalysis studies of two Au- and Ag-based initiators, namely, [3-(N-tert-butylacetamido)-1-(2-hydroxycyclohexyl)imidazol-2-ylidene]AuCl (1c) and [3-(N-tert-butylacetamido)-1-(2-hydroxycyclohexyl)imidazol-2-ylidene]AgCl (1b), for the bulk ring-opening polymerization Of L-lactide are reported. Specifically, gold complex 1c was obtained from silver complex 1b by the transmetalation reaction with (SMe2)AuCl. Silver complex 1b was synthesized by the treatment of 3-(N-tert-butylacetamido)-1-(2-hydroxycyclohexyl)imidazolium chloride (1a) with Ag2O, Compound la was synthesized directly from the reaction of N-tert-butyl-2-chloroacetamide, cyclohexene oxide, and imidazole. The molecular structures of 1a, 1b, and 1c have been determined by X-ray diffraction studies. The formation of neutral monomeric complexes with linear geometries at the metal centers was observed for both 1b and 1c. The An and Ag complexes 1c and 1b successfully catalyzed the bulk ring-opening polymerization of L-lactide at elevated temperatures under solvent-free melt conditions to produce moderate to low molecular weight polylactide polymers with narrow molecular weight distributions. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).