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A number of novel cationic carbonyl complexes of ruthenium and rhodium have been synthesised and characterised. The work also investigates the attack of nucleophiles on such species and examines the feasibility of these reactions as a possible first step in the catalytic production of organic esters. Mono and dipositive species of ruthenium have been effectively prepared by the reaction of [RuCl 2 (CO) 2{PPh3) 2 ] with AgBF4. The cationic 2species [RuCl(CO) 2 (PPh3) 2 ] [BF4 ] . 1/2(CH2C1 2 ) and [Ru(CO) 2 (PPh3) 2 ] [BF4] 22£H2cl2jiave been prepared under nitrogea The compound [Ru(CO)3(PPh3)2] [BF4 ] 2 has been synthesised in the presence of CO. The compound, [RuCl(CO)2(PPh3)2] [BF4 ] . l/2(CH2Cl2) reacts with 0*30 under CO to give [RuCl(COOCH3J I (00)2^*13)2. The compounds [Ru(CO) 2 (PPh3 ) 2 r [BF4 ] 2.CH2C1 2 and [Ru(CO) 3 (PPh3 ) 2 ] [BP4 ] 2 effectively form cis-[Ru(COOCH3)2(CO)2(PPh3)2] by the reaction of CHsONa in the presence of CO at room temperature. This dialkoxycarbonyl compound preparation from the dipositive species are energetically more favourable than the cis-[RuCl2(CO)2(PPh3)2L where the2reaction takes place at CO high pressure. The compound [Ru(CO)2(PPh3)2] [BF4 ] 2. CH2C1 2 reacts with NaBH4, Nal, cone. HC1 and CHsCOONa to give the dihydrido, diiodo, dichloro and bisethanoato compounds respectively. Cationic complexes of rhodium have been synthesised by the reaction of trans-[RhCl(CO)(L)2], (L = PPhs, AsPhs, PCys) with AgBF4 in the absence and presence of CO to give [Rh(CO|(L)2]_[BF4]~. n CH2C12 [where n = 1/2 or 3/2] and trans- [Rh(CO) 2 (L) 2 ] [BF4J~ respectively. These cations react with PONa (R = CH3/ C2Hs) to give [Rh(OR) (CO) (L) 2 ] and [Rh(COOR)(CO)(L) 2 ], (R = CH3, L = PPh3/ PCy3 ). The alkoxycarbonyl compound, [Rh(COOR) (CO) 2 (L) 2 ] is formed by the reaction of sodium alkoxide in the presence of CO, (when R = CH3, C2Hs, C3H7, then L = PPh3 and when R = CH3 then L = AsPh3). The alkoxo compound, Rh(OCH3) (CO) (L) 2, (L = PPh3 ) oxidatively adds CH3I to give [Rh(OCH3) (CH3 )I(CO) (L) 2 ]. The cation [Rh(CO)(L) 2 ] , reacts with RCOONa to give the carboxylato compounds, trans-[Rh(CCCR) (CO) (L) 2 L when L = PPh3 then R = CH3, when L = AsPh3 then R = H, CH3, C2H5_and when L = PCys then R = CH3. The compound [Rh(CO) 2 (SbPh3)3] [BF4J . CH2C12 has been formed from [RhCl(CO)(SbPh3)aJ with AgBF4 in the _presence of CO. The cation [Ru(CO) 2 (PPh3) 2 ] reacts with CH^p in the presence of CO (10 atmospheres) to give [Ru(CO)3(PPh3)2) and a trace amount of dimethylcarbonate. The same compound is obtained by using triethylamine in methanol under CO (10 atmospheres) at 65-70 C. Dimethylcarbonate rapidly reacts with Cl^ONa in contact with air to form a white precipitate, suggested to be Na2COj. Homogeneous solutions of [RuCl 2 (CO) 2 (PPh3 ) 2 ], [Ru(CO) 2 (PPh3 ) 2 r and [Rh(CO) (PPh3 ) 2 ] in dichloromethane produce benzene in the presence of CI^ONa in air. The cationic complexes of rhodium [Rh(CO)(L) 2 l , where L = PPh3, AsPh3, PCy3 and ruthenium complex [RuCl(CO) 2 (PPh3) 2 ] are effective catalysts for the hydrogenation of alkenes under hydrogen at atmospheric pressure and ambient temperature. The compounds .-have been characterised by analysis, infrared, H-NMR, P-NMR and C-NMR spectres copy and the organic products have been characterised by gas chromatography and in one case, GC/MS.

In an effort to explore new metal mediated reactivity and further the versatility of metal pincer chemistry, research in the Turculet group has targeted the synthesis of novel bis(phosphino)silyl PSiP pincer complexes. In this context, the synthesis and reactivity of Group 10 complexes featuring [Cy-PSiP] ([Cy-PSiP] = [?3-(2-Cy2PC6H4)2SiMe]⁻) ligation is described herein. The central silyl donor is anticipated to promote the formation of electron rich metal species capable of diverse and challenging reactivity. In the course of this work, it was found that [Cy-PSiP] ligation supports the synthesis of square planar PtII alkyl complexes that can mediate Si-H and Si-Cl bond cleavage chemistry. A cationic PtII species was accessed by treatment of [Cy-PSiP]PtMe with B(C6F5)3. The latter complex underwent B-C bond cleavage in the [MeB(C6F5)3]⁻ counteranion to produce [Cy-PSiP]Pt(C6F5). Examples of Si-C bond cleavage reactions at Pt0 and PtII centers were also observed. Related alkyl complexes of Ni and Pd were observed to undergo rearrangement processes involving net Si-C(sp2) and Si-C(sp3) bond cleavage. In the case of Ni these Si-C bond cleavage steps are reversible on the NMR timescale. Attempts to prepare a terminal hydride complex of the type [Cy-PSiP]MH (M = Pd, Pt) resulted in the isolation of ?2-Si-H coordination complexes of the type [Cy-PSi(µ-H)P]M, which were shown to undergo insertion of CO2 to form the corresponding formate species. In the presence of B(C6F5)3, these ?2-Si-H complexes were capable of mediating the catalytic reduction of CO2 to CH4 using hydrosilanes as the reducing agent. The synthesis and characterization of terminal, monomeric Pt hydroxide and alkoxide complexes of the type [Cy-PSiP]Pt(OR) (R= H, Ph, tBu) was achieved, and these complexes were shown to readily deprotonate relatively acidic C-H bonds in phenylacetylene and acetonitrile. A rare example of hydrogenolysis of the Pt-OR linkage with H2 was documented, as was an unusual example of Si-H addition across the Pt-OR bond to form Pt silyl species. While terminal anilido Pt complexes of the type [Cy-PSiP]Pt(NHAr) (Ar = Ph, 2,6-Me2C6H3, 2,6-iPr2C6H3) proved readily isolable, related Ni and Pd anilido species underwent rearrangement processes similar to those observed in their alkyl analogues. Terminal phosphido complexes supported by [Cy-PSiP] ligation were successfully isolated and characterized for all Group 10 metals. Lastly, the Pt and Pd coordination chemistry of a new PSiN pincer derivative was explored, and the amino donor arm of this pincer ligand was demonstrated to exhibit hemilabile coordination to the metal center.

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This thesis describes investigations by the author into the preparation of the oxazole heterocyclic system, by the use of rhodium carbenoid methodology. Chapter 1 is a review of the literature on the formation of oxazoles, by the reaction between diazocarbonyl compounds and nitrites. The various conditions that have been employed in the reaction are detailed, as well as developments into the understanding of its mechanism. Chapter 2 reports the study into the preparation of 4-functionalised oxazoles. A series of 4- benzenesulfonyloxazoles, oxazole-4-phosphates and oxazole-4-carbonitriles were prepared by a rhodium(II)-catalysed reaction. The effect of varying the rhodium(II) catalyst on oxazole formation is detailed. The oxazole-4-carbonitrile methodology was extended to form bis-oxazoles. Attempts to extend this chemisiry towards tris-oxazoles is discussed. Chapter 3 describes the synthesis of the oxazolylindole alkaloids pimprinine, pimprinethine and WS-30581A. This was achieved by the reaction of tert-butyl 3-diazoacetylindole-1- carboxylate with the appropriate nitrile, under rhodium(II) catalysis, followed by deprotection. Studies into varying the substituents at the 2- and 4-positions of the oxazole ring is described. Chapter 4 relates investigations into the synthesis of the cytotoxic cyclic peptides, diazonamide A and B, isolated from the ascidian, Diazona chinensis. These investigations were centred on key skeletal features: an oxazolylindole moiety, an oxazole based around (S)-valine and a functionalised benzofuranol. Model studies towards the oxazolylindole and the valine oxazole sections were undertaken, utilising rhodium carbenoid methodology to prepare the azote heterocycle. Formation of the benzofuranol model involved a one step deprotection and cyclisation, the precursor being prepared via a Claisen rearrangement and an ozonolysis. Chapter 5 contains the experimental data, whilst Chapter 6 contains the references.

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