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)5W(η1-PPh2CH2PPh2) (1) and (OC)5W(μ-PPh2CH2PPh2)W(CO)5 (2), have been synthesized from (OC)5WNH2Ph 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 13C{1H} and 31P{1H} NMR data suggest that this conformation may also be dominant in solution. Phosphorus−phosphorus coupling in 1 (2JPP = 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 (4JPC = 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)5WNH2Ph to give 2 is explained in terms of the substantial ligand conformation change required.