Molecular Structure of Co2(μ-Alkyne) Complex Containing Ph2PC5F6PPh2 Ligand

Oxidative-decarbonylation of Co2(CO) 6(μ-PhC≡CH) with Me3NO in the presence of an electron deficient ligand, Ph2PC5F6PPh2 (F6FOS), produces Co2 (CO) 4 (μ-PhC≡CH)(F6FOS), (1). The metrical values of 1 have been compared to those of the closely related cobalt carbonyl alkyne compound A containing (Z)-Ph2PCH=CHPPh2 (Z-dppe) ligand. Strikingly anomalous is an alkyne C≡C bond (1.34(1) Å in 1, which is somewhat elongated compared to A (1.31(1) Å). When taking a strong electron-withdrawing power of fluoride atom into account, F6FOS ligand appeared to reduce the π-back-donation ability of cobalt atom, making this bond shortened in comparison to the same bond in A. Bond lengthening in the alkyne C≡C bond in 1 is attributed to the enhanced electron donor ability of F6FOS compared to Z-dppe and can be understood by examining resonance structures of F6FOS ligand.