Alan C. Sentman,Szilárd Csihony,
Robert M. Waymouth,* andJames L. Hedrick*
IBM Almaden Research Center, 650 Harry Road,
San Jose, California 95120, and Department of Chemistry,
Stanford University, Stanford, California 94305
waymouth@stanford.edu; hedrick@almaden.ibm.com
Received August 18, 2004
Abstract:
N-Heterocyclic carbene (NHC) complexes with silver were
investigated as sources of unsaturated NHC carbene catalysts via thermal decomposition. The NHC complex (1-ethyl-3-methylimidazol-2-ylidene)silver(I) chloride is an ionic
liquid, and was found to catalyze the ring-opening polymerization of lactide at elevated temperatures to give narrowly
dispersed polylactide of predictable molecular weight. Silver-carbene complexes can also be used for the catalysis of small
molecule transesterification reactions. Thermolysis of the
silver complexes in the presence of CS2 yielded the zwitterionic CS2 adducts of the carbene, implicating the intermediacy of the free carbene in these reactions.
and
