The mixed-metal carbonyl cluster anion [Ru₃Ir(CO)₁₃]^– : synthesis, molecular structure, fluxionality, reactivity

The new cluster anion [Ru₃Ir(CO)₁₃]^–<b>1</b> was synthesized in high yield from [Ru₃(CO)₁₂] and [Ir(CO)₄]^–. The single-crystal X-ray structure analysis of the bis(triphenylphosphoranylidene)ammonium salt revealed the presence of two isomers, [Ru₃Ir(CO)₁₁(µ-CO)₂]^–<b>1a</b> and Ru₃Ir(CO)₉(µ-CO)₄]^–<b>1b</b> in the same crystal. Both <b>1a</b> and <b>1b</b> present a tetrahedral Ru₃Ir framework, differing only by the number of bridging carbonyl ligands. Variable-temperature ¹³C NMR spectroscopic studies of <b>1</b> revealed the fluxionality of the carbonyl ligands and the interconversion of both isomers in solution. Protonation of <b>1</b> gave the neutral cluster [HRu₃Ir(CO)₁₃] <b>2</b>, whereas reaction of <b>1</b> with molecular hydrogen yielded the anion [H₂Ru₃Ir(CO)₁₂]^–<b>3</b>. Either hydrogenation of <b>2</b> or protonation of <b>3</b> gave [H₃Ru₃Ir(CO)₁₂] <b>4</b>. The tetrahedral structure of the hydrido derivatives was confirmed by a single-crystal X-ray structure analysis of the bis(triphenylphosphoranylidene)ammonium salt of <b>3</b>.