Preparation of carbonyltungsten(0) complexes of 2-pyridylphosphines showing a stepwise coordination pattern by way of monodentate to chelate mode

2-Pyridylphosphines, R2PyP (R=Ph, NMe2; Py=2-pyridyl), were allowed to react with W(CO)5(thf) to afford the monocoordinated tungsten(0) complexes on the phosphorus [R2PyP][W(CO)5] and their structures were confirmed by X-ray crystallography. No ligation of the 2-pyridyl groups was found but a considerable p-donating effect of the dimethylamino groups in (Me2N)2PyP was observed. The monocoordinated complexes were irradiated with light to afford the chelate complexes [R2PyP][W(CO)4] by loss of one CO from the pentacarbonyls. X-ray structural analysis and spectroscopic data of [R2PyP][W(CO)4] indicated that the electron-donating effect of the nitrogen atom in the 2-pyridyl group upon the carbonyls is slightly larger than that of the phosphorus atom in spite of the reluctant coordination at the early stage of ligation.