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 (²J_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 (⁴J_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)₅WNH₂Ph to give 2 is explained in terms of the substantial ligand conformation change required.