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 L³ (L³ = 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)(L³)][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)(L³)][PF₆]₂ have been prepared via the reaction of [M(C₅Me₅)Cl₂]₂ with 2 mol equivalents of L³ and 4 of TlPF₆ in refluxing MeOH. Comparisons of the spectroscopic and crystallographic data for the metal(I) complexes reveal superior σ 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 H₂ is also described.