Four- and five-coordinate complexes of rhodium and iridium containing trifluorophosphine

Article abstract of DOI:10.1021/ic50105a004

Trifluorophosphine displaces coordinated cyclooctene from the complex [RhCl(C₈H₁₄)₂]₂ at room temperature and pressure to give an almost quantitative yield of the dimeric, chloro-bridged complex [RhCl(PF₃)₂]₂, which was previously accessible in only 2.6% yield. Trifluorophosphine also reacts with [IrCl(C₈H₁₄)₂]₂ to give as the final product a five-coordinate complex IrCl(PF₃)₄, though there is evidence for intermediate mixed cyclooctene-trifluorophosphine complexes. Both these and IrCl(PF₃)₄ readily decompose on warming to give the new compound [IrCl(PF₃)₂]₂. Metal-metal bonded structures are proposed for [MCl(PF₃)₂]₂ (M = Rh or Ir) in the solid state. The preparation of mononuclear complexes such as M(acac)-(PF₃)₂ and π-C₅H₅Rh(PF₃)₂ is also described. Nmr studies indicate that there is rapid exchange between free and coordinated PF₃ at room temperature in planar rhodium(I) complexes but not in π-C₅H₅Rh(PF₃)₂. The complexes [RhCl(PF₃)₂]₂ (in the presence of PF₃) and IrCl(PF₃)₄ are reduced by potassium amalgam in ether giving initially the new metal-mercury bonded complexes Hg[M(PF₃)₄]₂ and finally the known salts K[M(PF₃)₂]. The latter react with [RhCl(PF₃)₂]₂-PF₃ or IrCl(PF₃)₄ to give the dimeric metal-metal bonded complexes Rh₂(PF₃)₈ and Ir₂(PF₃)₈, which probably are structurally similar to the isomer of Co₂(CO)₈ without bridging CO's. Cleavage of Rh₂(PF₃)₈ with H₂ (25°, 1 atm) gives HRh(PF₃)₄ quantitatively. Five-coordinate metal-metal bonded complexes of general formula RM(PF₃)₄ [M = Rh or Ir, R = (C₆H₅)₃Sn or (C₆H₅)₃PAu; M = Ir, R = (C₆H₅)₃Pb] can be made by reaction of [M(PF₃)₄]^- with RCl. However there is no reaction between M (PF₃)₄ and (C₆H₅)₃SiCl or (C₆H₅)₃GeCl, indicating that Rh(PF₃)₄^- and Ir(PF₃)₄^- are poorer nucleophiles than Co(CO)₄^-. A more general route to compounds containing bonds between rhodium or iridium and a group IV element is the reaction between M₂(PF₃)₈ and a group IV hydride: M₂(PF₃)₈ + RH → RM(PF₃)₄ + HM(PF₃)₄ [R = (C₆H₅)₃Si, (C₂H₅O)₃Si, Cl₃Si, or (C₆H₅)₃Ge]. With triphenylgermane there is a subsequent slow reversible reaction HM(PF₃)₄ + RH ? H₂ + RM(PF₃)₄, while with (C₂H₅O)₃SiH and HSiCl₃, this reaction goes to completion. Kinetic studies indicate both reactions to be bimolecular, the rates depending on the transition element (Rh > Ir), the group IV element (Ge > Si), and the substituents on the group IV atom (Cl ～ C₂H₅O > C₆H₅). The reactions are compared with those believed to occur in the hydrosilation of Co₂(CO)₈.