Isonitrile-containing platinum-gold phosphine clusters

Abstract

PtAu-phosphine clusters with an isonitrile ligand on Pt or both Pt and Au can be synthesized from [Pt(AuPPh3)8]2+. The reaction of one equivalent of RNC (R = i-Pr,t-Bu) with [Pt(AuPPh3)8]2+ results in the addition of RNC to the central Pt, to form [Pt(RNC)(AuPPh3)8]2+. The addition of an excess of RNC results in the replacement of one of the Au-bonded PPh3 ligands to give [Pt(RNC)(AuRNC)(AuPPh3)7]2+. Treatment of [Pt(CO)(AuPPh3)8]2+ with an excess of RNC does not result in displacement of the Pt-bonded CO ligand but only one of the Au-bonded PPh3 ligands, to yield [Pt(CO)(AuRNC)(AuPPh3)7]2+. Ag adducts of all of these compounds can be prepared by the addition of one equivalent of AgNO3. The compounds have been characterized by IR and NMR (1H, 31P and 195Pt) spectroscopy and elemental analysis. The structures are thought to be isostructural with the reported [Pt(AgNO3)x(CO)y(AuPPh3)8](NO3)2 compounds, with x, y = 0, 1. NMR and IR data for these clusters are compared, and observed trends analysed in terms of σ-donor and π-acceptor considerations. A fragment molecular orbital analysis of [Pt(CO)(AuPPh3)8](NO3)2 is presented. The changes in bonding characteristics upon addition of CO to [Pt(AuPPh3)8](NO3)2 are examined and the decrease of the radial 2J(PtP) coupling constant is explained in terms of the results.