Studies of a reluctant ligand.: An X-ray crystallographic and NMR spectroscopic analysis of (OC)5W(η1-PPh2CH2PPh2) and its (OC)5W(μ-PPh2CH2PPh2)W(CO)5 derivative

Tungsten pentacarbonyl complexes, (OC)(5)W(eta(1)-PPh2CH2PPh2) (1) and (OC)(5)W(mu-PPh2CH2PPh2)W(CO)(5) (2), have been synthesized from (OC)(5)WNH2Ph and Ph2PCH2PPh2 in toluene, and their solid-state structures have been determined by single-crystal X-ray diffraction. The lone pair of electrons on the dangling phosphine in 1 is oriented toward the W(CO)(5) unit in the solid state, and C-13{H-1} and P-31{H-1} NMR data suggest that this conformation may also be dominant in solution. Phosphorus-phosphorus coupling in 1 ((2)J(PP) = 106 Hz) is significantly larger than in any previously reported complex of Ph2PCH2PPh2 and is highly dependent on changes in temperature and solvent. Also observed is an unprecedented long-range phosphorus-carbon coupling ((4)J(PC) = 3.0 Hz) between the dangling phosphine and the equatorial carbonyl carbons of 1, which is attributed to a conformational and/or "through-space" enhancement. On the basis of the structural and spectral data, the reluctance of 1 to react with (OC)(5)WNH2Ph to give 2 is explained in terms of the substantial ligand conformation change required.