Phosphine-Stabilized, Platinum-Gold And Palladium-Gold Cluster Compounds And Applications In Catalysis

This is a comprehensive review on the chemistry and spectroscopic properties of phosphine-stabilized, M-centered Au cluster compounds where M=platinum or palladium. The nuclearity of the clusters ranges from 3 (e.g. [Pt(NO3)(PPh(3))(2)(AuPPh(3))(2)](+)) to 25 (e.g. Pt2Ag13(AuPPh(3))(10)Cl-7). The latter consists of two Pt-centered icosahedral units sharing a common vertex, Many of the clusters contain additional metals such as Ag, Cu, or Hg in their periphery, Preparative methods are reviewed and organized by reaction type. Emphasis has been placed on reactions and transformations of preformed clusters so that the reader will acquire a useful knowledge of the reaction chemistry, Structural properties of the clusters are also described, The reactivity and structural properties of the clusters are rationalized in terms of an electron counting model and this is used throughout the review, Spectroscopic properties (e.g. nuclear magnetic resonance (NMR), fast atom bombardment mass, UV-visible, and X-ray photoelectron spectroscopy) of the clusters are described primarily for characterization; however, general trends are pointed out. Several applications in catalysis are also reviewed. Many of the clusters are good catalysts for Hz activation and can serve as potential models for bimetallic surfaces, Kinetic data for the H-2-D-2 equilibration reaction (H-2+D-2 reversible arrow 2HD) are given and discussed in terms of cluster composition and structure, The results provide some insight into the well-known synergism observed for Pt-Au and Pd-Au heterogeneous catalysts. The mechanism of catalytic H-2-D-2 equilibration under homogeneous conditions is also discussed. The cluster [Pt(AuPPh(3))(8)](2+) is an excellent catalyst for D-2(g)-H2O(1) isotope exchange in pyridine solution. This interesting and important reaction is described and kinetic results are related to other isotope exchange systems, A tentative mechanism is proposed based on NMR analysis of the reaction mixture. Finally, prospects for future studies are given, The recent discovery of the catalytic applications of these clusters provides renewed interest in this challenging field.