Chemical/structural/theoretical studies of heterometallic gold-M carbonyl phosphine clusters (M=nickel, palladium, platinum)

Experimental/theoretical explorations have been carried out in attempts to systematically delineate reaction growth-patterns of CO, PR₃-ligated bimetallic Au-M clusters (M=Ni, Pd, Pt). These include: (1) Formation of Au-Ni clusters from reactions between Au(PPh₃)Cl and [Ni ₆(CO)₁₂]2− at different Ni₆Au(I) mol ratios in order to reveal stages through which a given reaction occurs as the Ni₆/Au(I) mol ratio is increased. ESI ToF mass spectrometric measurements and comparative analysis of reaction products revealed that low Ni₆/Au(I) mol ratios gave rise to the formation of segregated gold and nickel ligated clusters. Only when the Ni₆/Au(I) mol ratio was increased did the reactions afford Au-enriched Au-Ni carbonyl phosphine clusters that transformed into Ni-enriched Au-Ni clusters at higher Ni ₆/Au(I) ratios. This research resulted in isolation and stereochemical characterization of a new Au-Ni cluster, [Au₇Ni₇(CO) ₁₀(PPh₃)₆]−. (2) Designed reactions between small preformed palladium clusters and appropriate Au(I) precursors in the presence of TlPF₆ unexpectedly gave rise to the first example of a high-nuclearity thallium-palladium cluster, [Tl₂Pd ₁₂(CO)₉(PEt₃)₉]2+. Its Tl₂Pd₁₂ core was initially presumed to be Au₂Pd ₁₂ from incorrect “heavy-atom” labeling in X-ray crystallographic analysis. Based upon structure-to-synthesis approach, it was prepared in 90% yield from reaction of Au(SMe₂)Cl and TlPF₆ with Pd ₄(CO)₅(PEt₃)₄. Its true identity was subsequently established from its direct preparation from TlPF₆ with Pd₄(CO)₅(PEt₃)₄, its now interpretable 31P{lcub}1H{rcub} NMR spectrum, and its elemental analysis. (3) In ongoing work to expand Au-Pt chemistry, the low-yield preparation and structural/theoretical analysis of Au₂Pt ₇(CO)₈(PPh₃)₆ containing a heretofore unknown metal-core geometry are presented along with extensive preparative attempts to obtain a reproducible high-yield synthesis. (4) 31 P{lcub}1H{rcub} NMR spectra were used to monitor the reversible chemical interconversion between Pd₂₃(CO)₂₀(PEt ₃)₁₀ and Pd₂₃(CO)₂₀(PEt₃) ₈ with seemingly unrelated metal-core geometries. The occurrence of this reversible transformation was based on the observed correlation between metal-core structures of two clusters. (5) Gradient-corrected DFT calculations performed on model cluster systems resulted in interpretations that accounted for a proposed reaction pathway concerning the formation of the Tl₂Pd ₁₂ cluster, an understanding why this cluster is preferentially formed instead of the (as yet) unknown Au₂Pd₁₂ cluster, and the uniqueness of palladium metal cluster chemistry.