Synthesis and redox chemistry of 1,1′-bis(diphenylphosphino)ferrocene derivatives of R2C2Co2(CO) 6 (R = MeO2C, CF3)

Article abstract of DOI:10.1016/S0022-328X(96)06590-4

Fe(C₅H₄PPh₂)₂ (dppf) undergoes facile thermal substitution reactions with R₂C₂Co₂(CO)₆ (R = MeO₂C, CF₃) to yield a variety of products. When R = MeO₂C, initial coordination gives μ²-(MeO₂C)₂C₂Co₂(CO)₅(η;¹-dppf); its crystal and molecular structure, monoclinic, P2₁/c, a = 8.954(3), b = 20.211(2) c = 23.836(5) A, β = 100.55(2)°, Z = 4, R1 = 0.0345 for 5764 reflections 1 > 2 σ (I), confirms the monodentate coordination mode for dppf. At low dppf/alkyne-complex ratios, oligomeric products with dppf ligands linking up to five (μ²-MeO₂C)₂C₂Co₂ modules have been characterised but, as the proportion of the phosphine ligand increases, unstable products, which include a η¹-μ-η¹ dppf configuration, are obtained as well. In contrast, for R = CF₃, only [(CF₃)₂C₂]Co₂(CO)₄(η²-dppf) is found in significant yield. A molecule with two different reduction centres, [μ²-(MeO₂C)₂C₂Co₂(CO)₅](μ-dppf)[Co₃(μ³-CPh)(CO)₈], was also characterised. Electrochemistry of the dppf complexes was characterised by fast ligand dissociation upon reduction of the (μ-alkyne)Co₂ redox centre and oxidation of coordinated dppf. There was no evidence for communication between redox centres.