Synthesis, spectroscopic and structural studies on rhodium-(I) and -(III) and iridium-(I) and -(III) selenoether and telluroether complexes involving organometallic co-ligands

Low and medium oxidation state organometallic complexes with triseleno- and telluro-ether ligands have been prepared. Reaction of [M(COD)Cl](2) (M=Rh or Ir) with two molar equivalents of L-3 (L-3=MeC(CH2ER)(3), E=Se, R=Me; E=Te, R=Me or Ph) and two molar equivalents of NH4PF6 at room temperature in CH2Cl2 affords the species [M(COD)(L-3)][PF6]. These complexes, which represent the first seleno- or telluro-ether complexes of Rh-I or Ir-I, have been characterised by analysis, IR and multinuclear NMR spectroscopy. The crystal structures of [Rh(COD){MeC(CH2SeMe)(3)}]PF6, [Ir(COD){MeC(CH2SeMe)(3)}]PF6, [Rh(COD){MeC(CH2TeMe)(3)}]PF6 and [Ir(COD){MeC(CH2TePh)(3)}]PF6 reveal distorted square pyramidal geometries. The rhodium(III) and iridium(III) complexes [M(C5Me5)(L-3)][PF6](2) have been prepared via the reaction of [M(C5Me5)Cl-2](2) with 2 mol equivalents of L-3 and 4 of TlPF6 in refluxing MeOH. Comparisons of the spectroscopic and crystallographic data for the metal(I) complexes reveal superior sigma donation by the ligand MeC(CH2TeMe)(3) compared with its selenoether analogue. In contrast, the medium oxidation state metal(III) complexes show enhanced donation by the selenoether ligand. The reaction of the COD complexes with H-2 is also described.