Silver N-heterocyclic carbene complexes as initiators for bulk ring-opening polymerization (ROP) of l-lactides |
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Authors: | Manoja K Samantaray Keliang Pang Prasenjit Ghosh |
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Institution: | a Department of Chemistry, and Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India b Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India c Department of Chemistry, Columbia University, 3000 Broadway, New York, NY 10027, USA |
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Abstract: | 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 Ag2O 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 Ag2O 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. |
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Keywords: | Carbenes Functionalized NHC Organometallic complex Silver-NHC complex |
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