First Example of a Gold(I) <i>N</i>‐Heterocyclic‐Carbene‐Based Initiator for the Bulk Ring‐Opening Polymerization of <scp>L</scp>‐Lactide

Abstract

Abstract 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 (SMe 2 )AuCl. Silver complex 1b was synthesized by the treatment of 3‐( N ‐ tert ‐butylacetamido)‐1‐(2‐hydroxycyclohexyl)imidazolium chloride ( 1a ) with Ag 2 O. Compound 1a 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 Au 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. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2006)