Terthienyl (HTTTH) forms part of the family of conjugated 5-membered heterocycles and although many novel conversions of thiophenes and their derivatives have been recorded, the coordination chemistry of terthienyl has been neglected. Dinuclear biscarbene complexes [(CO)5MC(OEt)TTTC(OEt)M(CO) 5l, and monocarbene complexes [M(CO) 5{C(OEt)TTTH}] of the transition metals Cr, Mo and W with terthienyl spacer units were prepared. The reactivity of these complexes with ammonia, their relative stability and their structural features were investigated. The study focuses on electron delocalization of the conjugated TTT moiety and the role of the TIT substituent in stabilizing the electrophilic carbene carbon. Terthienyl substrates are readily mono and dimetallated and the classical Fischer method for the synthesis of carbene complexes was used. Complexes were fully characterized and molecular structures were determined. A single crystal structure determination of the tungsten biscarbene complex indicated a planar configuration of the thienyl rings and partial de localization through the conjugated ring system. / Dissertation (MSc (Chemistry))--University of Pretoria, 2001. / Chemistry / unrestricted

The reactions of iodomethane, diiodomethane, and formaldehyde over stoichiometric, O-terminated, and Cl-terminated α-Cr₂O₃ surfaces, were studied by thermal desorption spectroscopy. Adsorbed formaldehyde forms dioxymethylene species on the nearly-stoichiometric surface that react primarily above 600 K. Dioxymethylene decomposes via a Cannizzaro-type process with dehydrogenation to formate, and hydrogenation to methoxide. Methoxide hydrogenation produces methane and methanol near 670 K. Formate decomposition occurs at 720 K, producing acetylene, carbon monoxide, carbon dioxide and formic acid. The site requirements for these reactions are a cation/anion site pair. When the surface cations are capped with Cl, the reactivity associated with dioxymethylene intermediates above 600 K is not observed. At higher coverages, polymerization to paraformaldehyde is observed on both surfaces, and decomposition to formaldehyde is observed at 400 K in thermal desorption. Iodomethane and diiodomethane are used as sources of methyl and methylene surface species, respectively. Methyl fragments on the stoichiometric surface dehydrogenate to surface methylene and hydrogen as a rate limiting step to produce ethylene and methane at 505 K. On the oxygen-terminated surface, the methyl fragments undergo dehydrogenation and coupling to ethylene at 425 K, undergo oxygen insertion to formaldehyde at 425 K, and produce carbon dioxide, formic acid, and water above 700 K from the dehydrogenation of formate. Methylene fragments on the stoichiometric surface undergo diffusion limited coupling to ethylene at 390 to 490 K and produce methane at 520 K from dehydrogenation. On the oxygen-terminated surface, methylene undergoes oxygen insertion to produce formaldehyde at 450 K, produce carbon monoxide, formaldehyde, and water at 695 K from dioxymethylene dehydrogenation, and produce carbon dioxide, formic acid, and water above 700 K from the dehydrogenation of formate. / Ph. D.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

D.Sc. / This study involves the preparation and characterization of new amino(thio) carbene complexes of gold(I) and gold(III). In addition the reactivity of bis(thiazolyl) aurate and the above mentioned carbene complexes are also described. Various thiazolyllithium reagents reacted with [AuCl(tht)] to yield bis(thiazolyl) aurate complexes of gold(I) which were isolated in crystalline form. These crystals contained solvent of crystallization and no structural determination of these aurates were possible. The latter compounds readily reacted with elemental sulphur by insertion of a sulphur atom into one of the Au-C bonds thereof Subsequent reaction with one molar equivalent of CF 3S03CH3 or CF3SO3H produced either carbene, [Au(CNRYS)(SC=NY§)] (Y = CCH 3=CH, C4H6; R = H, CH3), or thione, [Au(S=h‘TRY)(C=NYS)], complexes of gold(I) which spontaneously decomposed into gold(I) polymers ([Au(C=NYS)]. or [Au(S&=NY)].) and organic products (C=NYS or S=CNRYS). In an attempt to isolate the above-mentioned carbene or thione complexes bis(thiazolyl) aurate complexes were treated with two molar equivalents of CF3S03CH3 or CF3SO3H after sulphur insertion. Rather than the expected mixed carbene thione complexes, [Au(elsTRY§)(S=eNRY§)]CF 3S03, homoleptic rearrangement produced bis(carbene) complexes of gold(I) with unexpected counterions (Cl instead of CF 3SO3). Reaction of lithiated mercaptobenzothiazole with [AuCl(tht)] yielded a bis(thiolate) complex of gold(I), [Au(SC=NC 6H4 S-0)2]Li. Alkylation or protonation of this modified aurate complex resulted in the formation of gold polymers, [Au(S=NC 6H4 -0)]„, and organic products, S=§NRC6H4§-o, R=H, CH3 ). Oxidative addition of halogens to bis(thiazolyl) aurate complexes produced no isolable organometallic complexes. [AuC1 1]Li probably formed after repetitive oxidation addition (C1 2) and reductive elimination reaction (2-chlorothiazole). However, oxidation of these aurate complexes with SOC12 limited the reaction to one oxidative addition and one reductive elimination step to produce [AuCl(CNHYS)] (Y=CCH 3=CH, C6H4) after acidification. Reaction of the neutral mono(carbene) complex [Au(CNCCH 3=CHS)(C=NCCH3=CHS)] with C12, Br2 or 12 produced carbene complexes of gold(I), [AuX(6NHCCH 3=CH§)] (X=C1, Br, I), after reductive elimination of 2-halogeno-4-methylthiazole. Cationic bis(thiazolinylidene) complexes of gold(I) react readily with C1 2 and 12 to produce stable Ms(carbene) complexes of gold(III). However, oxidative addition on the same carbene complex by I2 is followed by a novel reductive elimination of (ICNii)cF SO to produce carbene complexes of gold(I), [AuI(CMN7- TTA )]. Alkylation (CF3SO3CH3) of 4-methylthiazole, bensothiazole and methylimidazole, followed by deprotonation (BuLi) produced free carbenes. These carbenes were trapped by reaction with [AuCl(tht)] to form carbene-chloro complexes of gold(I). Chloro(1,3- dimethylimidazolinylidene)gold(I) react readily with NaN 3 or AgNO3 to yield [AuX(CNCH3CH=CH1:TCH3)] (X = N3 or NO3 ). As part of this study the structures of several carbene complexes were determined, including five carbene complexes of gold(I) and one carbene complex of gold(III). Au-C bond lengths of between 1.92-2.13A were found with the largest Au-C separation in the carbene complex of gold(III), [Au(aNCH3CH=CHNCH3)2]CF3S03 . Certain complexes of gold(I) exhibit interesting Au...Au interactions (3.19-3.51A) resulting in the aggregation of gold atoms to form dimers and chains of gold(I) atoms. The structures of two related complexes of iron were also determined to investigate the effect of protonation on a neutral carbene precursor, [Fe(CO) 2Cp(C=CHCH=NNPh)], to form the cationic carbene complex, [Fe(C0) 2Cp(aCH=CHNHI:IPh)JCF3S03. Small changes in bond lengths and angles resulted upon carbene formation.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Graduation date: 1991

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

The central focus of this dissertation pertains to the synthesis and study of novel N-Heterocyclic carbene architectures. This pursuit has led to advances in carbine structure and bonding, and application of NHCs in materials chemistry in the role of monomer and catalyst / text

Not available / text

A unifying theme of the chemistry presented is the synthesis, study, and application of a novel N-heterocyclic carbenes. Pursuit of these materials has resulted in new advances in carbene structure and bonding, the discovery of highly-efficient reactions, and the development of new polymers with unusual properties. / text