REVERSIBLE SKELETAL REARRANGEMENT IN A CARBIDO CARBONYL CLUSTER INDUCED BY LIGAND SUBSTITUTION - SYNTHESIS AND CRYSTAL-STRUCTURE OF THE ANION [RH12C2(CO)23(AUPPH3)]-

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 prod ucing 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 P2(1)/n, Z = 4, a = 13.4 99(2), b = 32.789(3), c = 14.923(3) angstrom, beta = 101.26(2)-degrees ]. The loss of a CO ligand and the addition of the gold fragment resul t in major rearrangements in the Rh12C2 cluster yielding an unpreceden ted layered aggregation in which three fused trigonal prisms (two cont aining the carbide atoms) are recognizable. The Au(PPh3)+ fragment bri dges a Rh4 butterfly-shaped face of the Rh-atom skeleton. Phosphorus-3 1 NMR spectra at low temperature show that the solution structure is s omewhat different with the gold bonded to a Rh(A)Rh(B)Rh(B) face. The CO ligands are distributed in such a way as to achieve a regular charg e distribution among the metal atoms.