Photochemical generation of 16-electron [Rh(η5)-C5H5)-(PMe3)] and [Ir(η5-C5H5)(PMe3)] in low-temperature matrices: evidence for methane activation

Abstract

The photochemical reactions of [Rh(η⁵-C₅H₅)(PMe₃)(H)₂] and [Ir(η⁵-C₅H₅)(PMe₃)(H)₂] have been studied in Ar, CH₄, N₂ and CO-doped argon matrices by IR and UV/VIS spectroscopy. The UV photolysis in argon matrices results in the formation of the 16-electron complexes [M(η⁵-C₅H₅)(PMe₃)] with characteristic visible absorption maxima (M = Rh, λ_max 399 and 488 nm; M = Ir, λ_max, 436 and 526 nm). The reaction is partially reversed by long-wavelength photolysis. The conversion of [Rh(η⁵-C₅H₅)(PMe₃)(H)₂] to [Rh(η⁵-C₅H₅)(PMe₃)(Me)H] on photolysis in methane matrices is confirmed by extensive isotopie labelling studies and by the use of alternative precursors for the methyl hydride, viz.[Rh(η⁵-C₅H₅)(PMe₃)(η²-C₆F₆)] and [Rh(η⁵-C₅H₅)(PMe₃)(C₂H₄)], Evidence has also been obtained to show that irradiation of [Ir(η⁵-C₅H₅)(PMe₃)(H)₂] in methane yields [Ir(η⁵-C₅H₅)(PMe₃)(Me)H]. Photolysis of [M(η⁵-C₅H₅)(PMe₃)(H)₂]in N₂ and CO-doped Ar matrices generates [M(η⁵-C₅H₅)-(PMe₃)L](M = Rh or Ir, L = N₂ or CO).