Reductive functionalization of carbon dioxide to methyl acrylate at zerovalent tungsten

摘要

Alkali metal reduction of tungsten tetrachloride in the presence of excess trimethylphosphite and ethylene affords moderate yields of trans- tetrakis(trimethylphosphite)tungsten bis(ethylene). This easily prepared species bearing inexpensive ancillary ligands promotes the oxidative coupling of carbon dioxide and ethylene at ambient temperature to produce two isomeric tetrakis(trimethylphosphite)tungsten acrylate hydride complexes. These isomers vary by the κ ~2-O,O and κ ~3-C,C,O coordination mode of the acrylate ligand, and swiftly interconvert in solution as detected by 2D NMR spectroscopy. The CO _2-derived acrylate fragment may be released from the tungsten coordination sphere by treatment with methyl iodide to afford modest quantities of free methyl acrylate.