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

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

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

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

Five tri- and tetra-substituted electron-poor olefins containing a β-leaving group, initiated cationic polymerization of p-methoxystyrene with widely varying results. As the electrophilicity of the electron-poor olefins increased, the yields and molecular weights of the polymers formed decreased. The same was true when the excellent leaving group, trifluoromethanesulfonate, was replaced by the poorer leaving group, chloride. Another series of tri-substituted olefins was prepared and reacted with p-methoxystyrene in the presence of excess methyl methacrylate or styrene. Terpolymer was formed as a major product when the electron-poor olefin used contained an α-ester group. The yield of the terpolymer increased with the increasing electrophilicity of the electron-poor olefin. The reactions of methyl α-cyanoacrylate with a number of electron-rich olefins were also studied and found to give new types of adducts, such as Diels-Alder adducts and pyrans. All these reactions were suggested to go through the formation of a tetramethylene intermediate, a resonance hybrid of a zwitterion and spin paired biradical.

No description available.

This thesis describes a new catalytic activity of a commonly used metathesis catalyst and demonstrates the viability of directly coupling two powerful C-C bond forming strategies: cross-metathesis and ylide transformations, both proceeding via metal-catalysed carbene transfer. Catalytic C-C bond formation reactions are highly significant; my studies focus on such transformations involving metallocarbenes. Grubbs' 2^nd generation Ru catalyst is the most commonly used catalyst in olefin metathesis to generate thermodynamically preferred trans-olefms. During the course of my studies, I established that Grubbs 2^nd generation catalyst (0.5 mol%) can also dimerise diazoacetates to give cis-enediesters (maleates) in good to excellent yields (74-99%) with high stereoselectivity (Z:E>95:5). The reaction between two different diazoacetates, catalysed by Grubbs catalyst gave access to unsymmetrical cis-enediesters with high stereoselectivity (Z:E>95:5, generally 99:1). The catalyst was found to retain its alkene metathetical activity during diazo coupling; building on this latter observation a novel route to access dienyl dilactones by head-to-head dimerisation of unsaturated diazoacetates was developed. Cross-metathesis was found to be chemoselective in the presence of diazo functionality (when flanked by two carbonyl groups), allowing the functionalisation of tethered olefin. The elaborated diazocarbonyl olefms were subjected to Rh₂(OAc)₄ catalysed ylide formation and subsequent transformations. Significantly, one-pot cross-metathesis/ylide transformations (1,3-dipolar cycloaddition and [2,3]-simgatropic rearrangement) also proved to be viable, establishing that the spent Ru catalyst following metathesis does not affect the subsequent Rh(II)-catalysed transformation.