FORMATION AND CHARACTERIZATION OF A HYDRIDOTANTALACYCLOPROPANE COMPLEX FROM THE PHOTO-INDUCED β-HYDRIDE ELIMINATION OF DI-η5-CYCLOPENTADIENYLETHYL(CARBONYL)TANTALUM

Article abstract of DOI:10.1016/0022-328X(84)85077-9

A reaction between Cp2TaCl2 and 2 equivalents of C2H5MgBr in refluxing dimethoxyethane has produced the hydrido-ethylene complex Cp2Ta(C2H4)H in 62percent yield.Acid hydrolysis of Cp2Ta(C2H4)H yields Cp2TaCl2 and ethane, whereas the ethylene ligand can be displaced by PEt3 under photochemical conditions to yield Cp2Ta(PEt3)H.A reaction between Cp2Ta(C2H4)H and carbon monoxide in toluene at 80 deg C results in CO-induced insertion of the ethylene ligand into the Ta-H bond, and formation of Cp2Ta(CO)C2H5 in 56percent yield.Photolysis of Cp2Ta(CO)C2H5 in hydrocarbon solventsgenerates Cp2Ta(C2H4)H as well as Cp2Ta(CO)H by a process of CO dissociation and β-hydride elimination. 1H NMR studies on Cp2Ta(C2H4)H demonstrate that the ethylene ligand does not rotate in solution up to 120 deg C. 1H and 13C NMR studies indicate a configuration for Cp2Ta(C2H4)H in which the ethylene C=C axis lies in the symmetry plane of the molecule, and together with the chemical degradation data are consistent with a tantalacyclopropane formulation for this molecule.