Chemistry of iridium carbonyl clusters. Synthesis and chemical characterization of the hexanuclear anions [Ir6(CO)15(CO2R)]–(R = Me or Et) and [Ir6(CO)14(CO2Me)2]2–. Crystal and molecular structure of [N(PPh3)2][Ir6(µ-CO)4(CO)11(CO2Me)]

Abstract

The anions [Ir₆(CO)₁₅(CO₂R)]^–(R = Me or Et) and [Ir₆(CO)₁₄(CO₂Me)₂]^2– have been prepared by reacting [Ir₆(CO)₁₆] with Na(OR) in dry alcohol under an atmosphere of carbon monoxide. The reaction of [Ir₆(CO)₁₅(CO₂Me)]^– with primary and secondary alcohols such as EtOH and PrⁱOH gives rise to specific alcoholysis. The anions [Ir₆(CO)₁₅(CO₂R)]^–( R = Me or Et) and [Ir₆(CO)_14–(CO₂Me)₂]^2– react with acids in tetrahydrofuran solution to give quantitatively [Ir₆(CO)₁₆]. The chemical and spectroscopic characterization of the hexanuclear anions is reported. Crystals of [N(PPh₃)₂][Ir₆(CO)₁₅(CO₂Me)] are triclinic, space group P, with unit-cell dimensions a= 10.813(3), b= 16.613(3), c= 16.061(2)Å, α= 97.96(1), β= 96.20(1), γ= 94.58(2)°, and Z= 2. The X-ray structure has been solved by the heavy-atom method and refined by least squares to a final conventional R of 0.033 for 5 291 independent observed reflections. The anion consists of a slightly distorted octahedron of iridium atoms with eleven terminal and four edge-bridging CO groups and a methoxycarbonyl group σ-bonded to a metal atom. The Ir–Ir bond lengths are in the range 2.703(1)–2.870(1)Å, with an average value of 2.793 Å. Other average bond distances are Ir–C_terminal 1.878 and C–O_terminal 1.135 Å.