The syntheses and reactivity of four- and five-membered metallacycles of platinum and palladium.

Chapter 1 reviews the literature concerning the synthesis and reactivity of oxodimethyl- enemethane metal complexes and their applications in organic synthesis. The preparation of metal-ureylene complexes and amino acid complexes of platinum are also discussed. Chapter 2 describes the synthesis of metallaphosphetane-3-oxide complexes of platinum and palladium, [M {lcub}CH(R)P(O)(Ph)CHR{rcub} L2]. Crystallographic and n.m.r. evidence for benzoyl substituted complexes, indicates that the four-membered rings are puckered, with the phosphoryl oxygen adopting an equatorial environment. The ligand substitution reactions of platinum analogues are also discussed. The preparation of new platina-2,4,3-diazaphosphetidine-3-oxide complexes, [Pt{lcub}N(R)P(O)(Ph)NR{rcub}L2] is presented in Chapter 3. An X-ray crystal structure determination on an N,N -diphenyl derivative indicates that the four-membered metalla-cyclic ring is almost planar, the nitrogen atoms of which show sp2 hybrid character. An investigation into the insertion reactions of the N,N'-dihydrogen derivatives with dimethyl acetylenedicarboxylate resulted in the isolation of six-membered platinacyclic products, characterised by n.m.r. and i.r. spectroscopy. Attempts to prepare a similar insertion product using hexafluorobut-2-yne, led only to the formation of an organic polymeric material. The formation of a novel four-membered ring species containing a phosphin-imine functionality [Pt{lcub}SP(=NPh)(Ph)NPh{rcub}L2] is also described in Chapter 3. The phos-phinimine group was shown to have Lewis base capabilities and also underwent Wittig-type reactions with C=O and C=S containing molecules to form [Pt{lcub}SP(O)(Ph)NPh{rcub}L2] and [Pt{lcub}SP(S)(Ph)S)L2] ring systems respectively. The formation and characterisation of phosphonato, phosphato and arsonato complexes of platinum(II) are described in Chapter 4. The molecular structure of a bis(phosphine)phos- phonato complex establishes the presence of a slightly puckered four-membered ring with the phosphoryl oxygen adopting an equatorial position. The decomposition in solution of a bis(benzyldiphenylphosphine) analogue led to the formation of the di-orthometallated product cis-[Pt{lcub}C6H4CH2PPh2{rcub}2], as shown by X-ray crystallography. Chapter 5 describes the synthesis of five-membered platinacycles containing amino acid derivatives, [Pt{lcub}N(R2)-CH(R1)-C(O)O{rcub}L2]. An X-ray crystal structure determination on an [N-acetylglycinato(2-)-N,O] complex, indicated the presence of an almost planar five- membered ring that contains substantial electron delocalisation within the carboxylate and amide functionalities. The reaction of these complexes in ethanol with carbon monoxide or sulphur dioxide led to the formation of bis(ethoxycarbonyl) or bis(ethylsulphonato) metal complexes respectively. The final Chapter investigates the syntheses of several new five-membered metallacyclic species which contain metal bonds to carbon, nitrogen, oxygen or sulphur. The isolation of the metallaoxacyclopentenone ring system [Pt{lcub}CH=C(NHCOMe)C(O)O{rcub}L2], formed via the rearrangement of an initially produced [Pt{lcub}N(COMe)C(=CH2)C(O)O{rcub}L2] species, was confirmed by a single crystal X-ray diffraction study. The natures of the other complexes were examined using n.m.r. and i.r. spectroscopy.