STUDIES OF A RELUCTANT LIGAND - AN X-RAY CRYSTALLOGRAPHIC AND NMR SPECTROSCOPIC ANALYSIS OF (OC)(5)W(ETA(1)-PPH2CH2PPH2) AND ITS (OC)(5)W(MU-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 pa ir 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. Phos phorus-phosphorus coupling in 1 ((2)J(PP) = 106 Hz) is significantly l arger than in any previously reported complex of Ph2PCH2PPh2 and is hi ghly 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 carbo ns of 1, which is attributed to a conformational and/or ''through-spac e'' 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.