Synthesis, molecular structure, and molybdenum complexes of 1,1′-bis(diphenylphosphino)cobaltocene

The synthesis of 1,1′-bis(diphenylphosphino)cobaltocene (1), (C₅H₄PPh₂)₂Co, from TlC₅H₄PPh₂ and CoCl₂ is described. The ligand 1 coordinates to one Mo(CO)₄ fragment as a chelating bidentate ligand to form [Co(C₅H₄PPh₂)₂] [Mo(CO)₄] (2) and to two Mo(CO)₅ fragments as a bridging bidentate ligand to form [Co(C₅H₄PPh₂)₂] [Mo(CO)₅]₂ (3). Molecular structure determinations have been carried out on compounds 1 and 3. Compound 1 crystallizes in the monoclinic space group P2₁/c with cell dimensions a = 8.5966 (16) Å, b = 18.765 (4) Å, c = 8.8137 (15) Å, β = 99.702 (14)°, Z = 2, and ρ = 1.32 g cm^-3. The structure was solved from 1735 observed reflections (F > 6σ(F)) and refined to final residuals of R = 0.033 and R_w = 0.041. Compound 3 crystallizes in the monoclinic space group C2/c with a = 16.651 (5) Å, b = 12.669 (6) Å, c = 26.322 (9) Å, β = 99.42 (2)°, Z = 4, and ρ = 1.47 g cm^-3. The structure was solved from 1474 reflections (F > 6σ(F)) and refined to final residuals of R = 0.048 and R_w = 0.060. The puckering of the substituted cyclopentadienyl ring of 1 is interpreted with the aid of molecular orbital calculations. Cyclic voltammetry of 1 and Fe(C₅H₄PPh₂)₂ (4) and their complexes indicate that substitution of the cyclopentadienyl ring and coordination of 1 and 4 to molybdenum carbonyl fragments affects both the redox potential and electrochemical reversibility of electron-transfer processes occurring at cobalt and iron.