Abstract
Silver complexes of amido-functionalized and nonfunctionalized
N-heterocyclic carbenes have been synthesized and structurally characterized. These complexes efficiently catalyze the ring-opening polymerization (ROP) of
l-lactide under solvent-free melt conditions.
Synthetic, structural and catalysis studies of two silver complexes namely, {[1-(2,4,6-trimethylphenyl)-3-(
N-phenylacetamido)imidazol-2-ylidene]
2Ag}
+Cl
−
1b, supported over an amido-functionalized
N-heterocyclic carbene ligand, and [1-(
i-propyl)-3-(benzyl)imidazol-2-ylidene]AgCl
2b, supported over a non-functionalized
N-heterocyclic carbene ligand, are reported. Specifically,
1b, a cationic complex bearing 2:1 NHC ligand to metal ratio, was obtained from the reaction of 1-(2,4,6-trimethylphenyl)-3-(
N-phenylacetamido)imidazolium chloride
1a with Ag
2O in 52% yield. The corresponding
1a was synthesized by the alkylation reaction of 1-(2,4,6-trimethylphenylimidazole) with
N-phenyl chloroacetamide in 73% yield. The other silver complex
2b, a neutral complex bearing 1:1 NHC ligand to metal ratio, was obtained from the reaction of 1-(
i-propyl)-3-(benzyl)imidazolium chloride
2a with Ag
2O in 42% yield. The
2a was synthesized by the alkylation reaction of 1-(
i-propylimidazole) with benzyl chloride in 45% yield. The molecular structures of the imidazolium chloride,
1a, and the silver complexes,
1b and
2b, have been determined by X-ray diffraction studies. The silver complexes,
1b and
2b, successfully catalyze bulk ring-opening polymerization (ROP) of
l-lactides at elevated temperatures under solvent-free melt conditions producing moderate to low molecular weight polylactide polymers having narrow molecular weight distributions.