2,2′-Bibenzimidazolate anions as bridging ligands in cationic heteronuclear gold(I)–rhodium(I) complexes. Crystal structure of [(Ph3P)2Au2(µ-bbzim)Rh(cod)][ClO4]·CHCl3

Abstract

Heterobinuclear complexes of the general formula [LAu(µ-Hbbzim)RhR][ClO₄][L = P(OMe)₃ or PPh₃; R = cyclo-octa-1,5-diene (cod) or norborna-2,5-diene (nbd)] have been prepared by treatment of [Rh(Hbbzim)R] with Ag[ClO₄] and [AuClL]. Binuclear 2,2′-bibenzimidazolate gold(I)(bbzim = dianion of 2,2′-bibenzimidazole) complexes of the type [Au₂(bbzim)L₂][L = P(OMe)₃ or PPh₃; L₂= bis(diphenylphosphino)methane (dppm) or 1,2-bis(diphenylphosphino)ethane (dppe)] react with [Rh(cod)(OCMe₂)_x][ClO₄] to give new heterotrinuclear complexes of general formula [L₂Au₂(µ-bbzim)Rh(cod)][ClO₄]. Bubbling of carbon monoxide through solutions of the complexes generally leads to the formation of the corresponding dicarbonylrhodium species. Nonetheless, [(Ph₃P)Au(µ-Hbbzim)Rh(cod)][ClO₄] reacts with carbon monoxide to yield [(Ph₃P)₂Au₂(µ-bbzim)Rh(CO)₂][ClO₄] and [Rh(H₂bbzim)(CO)₂][ClO₄]. Other related monocarbonyls are also described. The structure of the chloroform solvate of the compound [(Ph₃P)₂Au₂(µ-bbzim)Rh(cod)][ClO₄] has been determined by X-ray methods; it crystallizes in the triclinic space group P with a= 20.972(14), b= 11.324(9), c= 14.425(10)Å, α= 64.00(7), β= 85.84(6), γ= 91.18(6)°, and Z= 2. The structure has been solved by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.078 for 2 460 observed reflections. The bbzim dianion co-ordinates to the metal atoms in an unsymmetrical tetradentate manner: it chelates to one Rh atom through two N atoms from both imidazole rings and is bonded to two Au atoms through the other two N atoms of the imidazole rings. The co-ordination at the Rh atom also involves a cod molecule interacting through the two double bonds. The co-ordination at the Au atoms is completed by a PPh₃ ligand and is essentially linear. A short intramolecular Au ⋯ Au contact [3.134(4)Å] is observed in the complex.