Thiocarbonyl and selenocarbonyl complexes of iridium
The results to be described and discussed in this thesis concern synthesis and reactivity of iridium(I) and (III) complexes containing thiocarbonyl or selenocarbonyl ligands. Chapter 1 comprises: a review of Vaska's compound, IrCl(CO) (PPh3)2 and related species, covering syntheses, structure and bonding and reactions of this very widely studied moiety; and brief reviews of metal-thiocarbonyl syntheses and reactions and metal-selenocarbonyl chemistry. These three reviews background the themes developed in this work; of preparations and reactions, particularly ligand reactions, of thiocarbonyl and selenocarbonyl analogues of Vaska's compound and species derived from IrCl(CE)(PPh3)2, E = S, Se. A new synthesis of IrCl(CS)(PPh3)2 is described in Chapter 2. The route employed involves preparation of dithioester complexes and facets of the reactivity of these species have been considered and a number of metallocycle derivatives prepared. Reductions of coordinated-thiocarbonyl groups have been considered; IrH(CS)(PPh3)3 was transformed into IrH2(SMe)(PPh3)3 by treatment with hydrogen, while the thiocarbonyl cation complexes [IrClX(CO)(CS)-(PPh3)2]+ were treated with borohydride to afford thioformyl species. Iridium alkyl, thiocarbonyl complexes have been prepared, and transformed by reaction with dithiocarbamate ion to yield monohapto-thioacetyl derivatives. The preparation of IrCl(CSe)(PPh3)2, the selenocarbonyl analogue of Vaska's compound is reported in Chapter 3. The synthesis utilizes carbon diselenide as the selenocarbonyl source, and involves a four-step conversion of a dihapto-carbon diselenide adduct complex to the iridium(I) selenocarbonyl species. Reactions of a range of iridium(I) complexes with carbon diselenide are described, including the preparation of a complex including three CSe2 groups. Reactions of IrCl(CSe)(PPh3)2 have been studied and several iridium(I) and (III) selenocarbonyl compounds prepared. The ready reduction of IrCl(CSe)(PPh3)2 (in the presence of phosphine) by borohydride to give IrH2(SeMe)(PPh3)3 is described and comparisons are drawn between the relative reactivities of iridium thiocarbonyl and selenocarbonyl groups, in analogous species, with nucleophiles. It is concluded the Ir-CSe system is more reactive under similar conditions. Metallocycle derivatives of iridium selenocarbonyl, diselenomethylester complexes have been characterised.