Dinuclear pentafluorophenyl compounds of rhodium(III) with anionic bridging ligands. Molecular structures of [P(CH2Ph)Ph3]2[{Rh(C6F5)3}2(µ-SCN)2] and [P(CH2Ph)Ph3]2[{Rh(C6F5)3}2(µ-CO3)]

Abstract

Homodinuclear anionic rhodium(III) complexes of formula [{Rh(C₆F₅)₃}₂(µ-X)₂]^2–(X = Br 2, I 3, SCN 4, MeCO₂7, CF₃CO₂8 or NO₃9) or [{Rh(C₆F₅)₃}₂(µ-C₂O₄)]^2–10 have been prepared by treating the anionic derivative [{Rh(C₆F₅)₃}₂(µ-Cl)₂]^2–1 with the appropriate alkali-metal or silver salt. Complex 4 has also been obtained from [Rh(C₆F₅)₅]^2– and AgSCN, at 0 °C in CH₂Cl₂. The reaction between [Rh(C₆F₅)₅]^2– and the solvated species [Rh(C₆F₅)₃(Et₂O)_x] rendered [{Rh(C₆F₅)₃}₂(µ-OH)₂]^2–6 which reacts with CO₂ giving [{Rh(C₆F₅)₃}₂(µ-CO₃)]^2–11. The tetranuclear [{Rh(C₆F₅)₃}₄(µ-CN)₄]^4– complex 5 has been prepared by the reaction of [Rh(C₆F₅)₅]^2– with AgCN. The structures of 4 and 11 have been established by single-crystal X-ray diffraction studies: 4, triclinic, space group P, a= 11.954(2), b= 13.053(2), c= 15.236(3)Å, α= 89.94(1), β= 100.33(1), γ= 104.89(2)°, Z= 1, R=R′= 0.052 for 3692 observed reflections; 11, monoclinic, space group C2/c, a= 28.306(4), b= 13.413(2), c= 45.245(7)Å, β= 101.42(1)°, Z= 8, R= 0.069 and R′= 0.070 for 6142 observed reflections. Both anionic complexes are dinuclear with two Rh(C₆F₅)₃ units linked through a centrosymmetric double thiocyanate bridge in 4 or a tridentate bridging CO₃^2– group in 11, co-ordinated in an unusual µ-1 : 2κ²O, 1κO′, 2κO″ fashion. In both complexes the five co-ordinated metal centres exhibit square-pyramidal arrangements of the ligands with a slight asymmetry in the bonding mode of the basal C₆F₅ groups which gives rise to short interatomic Rh ⋯o-F distances.