SYNTHESIS AND REDOX CHEMISTRY OF 1,1'-BIS(DIPHENYLPHOSPHINO) FERROCENE DERIVATIVES OF R(2)C(2)CO(2)(CO)(6) (R=MEO(2)C, CF3)

Fe(C(5)H(4)PPh(2))(2) (dppf) undergoes facile thermal substitution rea ctions with R(2)C(2)Co(2)(CO)(6) (R = MeO(2)C, CF3) to yield a variety of products. When R = MeO(2)C, initial coordination gives mu(2)-(MeO( 2)C)(2)C2Co2(CO)(5)(eta(1)-dppf); its crystal and molecular structure, monoclinic, P2(1)/c, a = 8.954(3), b = 20.211(2) c = 23.836(5)Angstro m, beta = 100.55(2)degrees, Z = 4, R1 = 0.0345 for 5764 reflections I > 2 sigma(I), confirms the monodentate coordination mode for dppf. At low dppf/alkyne-complex ratios, oligomeric products with dppf ligands linking up to five (mu(2)-MeO(2)C)(2)C2Co2 modules have been character ised but, as the proportion of the phosphine ligand increases, unstabl e products, which include a eta(1)-mu-eta(1) dppf configuration, are o btained as well. In contrast, for R = CF3, only [(CF3)(2)C-2]Co-2(CO)( 4)(eta(2)-dppf) is found in significant yield. A molecule with two dif ferent reduction centres, (2)C2Co2(CO)(5)](mu-dppf)[Co-3(mu(3)-CPh)(CO )(8)], was also characterised. Electrochemistry of the dppf complexes was characterised by fast ligand dissociation upon reduction of the (m u-alkyne)Co-2 redox centre and oxidation of coordinated dppf. There wa s no evidence for communication between redox centres.