Reversible skeletal rearrangement in a carbido carbonyl cluster induced by ligand substitution. Synthesis and crystal structure of the anion [Rh12C2(CO)23(AuPPh3)]–

Abstract

The mixed-metal carbido carbonyl cluster anion [Rh₁₂C₂(CO)₂₃(AuPPh₃)]^– has been obtained by reaction of [Rh₁₂C₂(CO)₂₄]^2– with [Au(PPh₃)Cl]. It is an intermediate species in the previously reported reaction producing the two related clusters [Rh₁₀C₂(CO)₁₈(AuPPh₃)₄] and [Rh₁₀C₂(CO)₂₀(AuPPh₃)₄] and reacts with CO regenerating the starting dianion. The molecular structure of the [NEt₄]⁺ salt has been determined by X-ray diffraction analysis [monoclinic, space group P2₁/n, Z= 4, a= 13.499(2), b= 32.789(3), c= 14.923(3)Å, β= 101.26(2)°]. The loss of a CO ligand and the addition of the gold fragment result in major rearrangements in the Rh₁₂C₂ cluster yielding an unprecedented layered aggregation in which three fused trigonal prisms (two containing the carbide atoms) are recognizable. The Au(PPh₃)⁺ fragment bridges a Rh₄ butterfly-shaped face of the Rh-atom skeleton. Phosphorus-31 NMR spectra at low temperature show that the solution structure is somewhat different with the gold bonded to a Rh_ARh_BRh_B face. The CO ligands are distributed in such a way as to achieve a regular charge distribution among the metal atoms.