Synthetic and spectroscopic studies on heterometallic clusters of platinum
This Thesis describes the synthesis and structural characterisation of a range of heterometallic cluster compounds of platinum. Chapter 1 reviews the current knowledge in this area and gives examples of the kinds of cluster compounds which have been characterised, with some emphasis on their mode of synthesis and their structural and spectroscopic characterisation. The structures of the cluster compounds are rationalised in terms of the triangular Pt3 unit which dominates the cluster chemistry of platinum. The bonding in the simplest triplatinum cluster compounds is analysed and is used as a basis for understanding the interconversion of platinum cluster compounds and the formation of heterometallic platinum-gold cluster compounds. Chapter 2 describes the synthesis and characterisation of the homometallic platinum cluster compounds which are convenient precursors for the formation of heterometallic cluster compounds. A general synthetic route to the platinum carbonyl phosphine clusters has been developed and the exchange of bridging CO and S02 ligands in this type of cluster was investigated. The synthesis of a new type of anionic 44 electron triplatinum cluster, [Pt3(μ-S02)2(μ-X)(PR3)3]¯ described. The syntheses of heterometallic clusters from the trianguloplatinum cluster compounds are reported in Chapter 3. The use of [AuPR3] as a capping fragment generates clusters with a tetrahedral Pt3Au framework. The synthesis and characterisation of two novel "sandwich" compounds are reported in which a gold or copper atom is coordinated between two parallel triplatinum units. A full single crystal X-ray crystallographic study has been carried out on each of these compounds and their geometric parameters contrasted. Chapter 4 describes the reactions of the platinum-sulphide complex [Pt2(μ-S)(CO)(PPh3)3]. This compound is found to be chemically robust. The pt-Pt bond has so far proved resistant to insertion reactions and only the ligands trans to the sulphur atom are readily exchanged. The bridging sulphido- group appears to have an extensive coordination chemistry which has lead to the synthesis of some heterometallic complexes. This property does not, as yet, provide a route into cluster formation but instead produces complexes which are aggregates of metal atoms. The application of 31P and 195Pt NMR studies to the characterisation of platinum cluster compounds is discussed in Chapter 5. The solution NMR spectra of compounds synthesised in the course of this research are described and analysed in detail. A large amount of NMR data for homometallic triplatinum clusters has been gathered and it has been possible to characterise a number of such compounds having relatively low symmetry. The heterometallic complexes described in Chapters 3 and 4 have also been characterised using NMR spectroscopy by considering the extra MPR3 fragments as perturbations on the spectra of the compounds from which they were derived. Analysis of the complex spectra obtained for such compounds was greatly assisted by the use of computer simulation techniques.