2-[Bis(diphenylphosphino)methyl]pyridine (PNP) Derivatives of Rhenium Carbonyl. Crystal and Molecular Structure of Re₂(μ-PPh₂)(μ-η¹, η⁴-CHPPh₂C₅H₄N)(CO)₇

Two new 2-[bis(diphenylphosphino)methyl]pyridine (PNP) complexes of rhenium have been synthesized. Re₂(η²,η²-PNP)(CO)₈ was synthesized from Re₂(CO)₈(μ-H)(μ-CH=CHC₄H₉) and an excess of PNP in CH₂Cl₂ solution. Re₂(η²,η²-PNP)(CO)₈ was characterized by IR, mass, and ¹H, ³¹P, and ¹³C NMR spectroscopies. The structure of Re₂(η²,η²-PNP)(CO)₈ is based on Re₂(CO)₁₀ in which one eq-CO on each Re has been replaced with phosphino groups from the bridging PNP ligand. The pyridyl group is not coordinated. Re₂(η²,η²-PNP)(CO)₈ thermally decarbonylates in toluene solution to afford Re₂(μ-PPh₂)(μ-η¹,η ⁴-CHPPh₂C₆H₄N)(CO)₇ in high yield. Re₂(μ-PPh₂)(μ-η¹,η ⁴-CHPPh₂C₅H₄N)(CO)₇ was characterized spectroscopically and by a single-crystal X-ray diffraction [P, a = 10.906 (10) Å, b = 18.164 (9) Å, c = 10.973 (6) Å, α = 98.56 (5)°, β = 119.12 (6)°, γ = 94.14 (8)°, Z = 2, D = 1.951 g cm^-3, R = 0.045]. The molecular structure was found to consist of two octahedral rhenium centers joined by a μ-PPh₂ ligand and a μ-C₅H₄NCHPPh₂ (PN) moiety. These two bridges are the fragments that result when the coordinated PNP in Re₂(η²,η²-PNP)(CO)₈ undergoes P-C bond activation. The PN group chelates in a bidentate manner to one Re and is σ-bonded via the methine C to the other Re. No Re-Re bond exists (4.189 Å).