No description available.

A series of closely related lithium aryl thiolates with pyridine as a donor ligand have been prepared. X-ray structure determination (Dr. W. Clegg) has shown that [PKSLi.(NC(_5)H(_5))] crystallises as an infinite chain polymer. Insertion of a methylene group between the phenyl ring and sulphur as in (PhCH(_2)SLi .NC(_5)H(_5). ] (_oo) produced an infinitely folded ladder polymer with Li-S rungs, while introduction of an 0-methyl group produces the monomeric complex [o-MeC(_6)H(_4)SLi .(NC(_5)H(_5))(_3)].The unusual symmetrical complex [Li(_14) (SCH(_2)Ph)(_12) S(TMEDA.)(_6)] has been prepared, in which a central sulphur atom is surrounded by a distorted cube of lithium atoms, each edge of which is bridged by a benzyl thiolate group such that the twelve S atoms form a cubo- octahedron: a further six Li atoms form a larger outer octahedron. When TMEDA is present in excess it appears that both PhSLi and PhCH(_2)SLi form dimeric compounds with a central Li(_2)S(_2) ring but structure determination of these complexes is incomplete.[PhOOSLi.TMEDA](_2)has been prepared and crystallises as a centrosymmetric dimer containing a chair shaped central eight membered (OOSLi)(_2) ring with the Li atoms out of the (COS)(-2), molecular plane. Lithiation of the related acids PhOOOH and PhCSSH has been carried out in the presence of TMEDA but crystal growth has so far been unsuccessful. Ab initio m.o. calculations on related model compounds are included. A preliminary study has been carried out on the lithiation of the thio-oxime (Ph(_2) C-NSH). Results were encouraging but detailed investigation is needed. The reaction of S(_4) N(_4) with BI(_3) produces, not the expected adduct, S(_4)N(_4) .BI(_3) , but an intractable polymer, empirical formula, S(_3)N(_3)BI. Other adducts of S(_4).N(_4) and (PhCN_2) S(_2))(_2), were prepared but were unsuitable for further reactions. The reaction of lithium borohydride and sulphur in THF to produce sulphurated lithium borohydride has been modified to give a controllable reaction. Further reaction with TMEDA gives clear orange crystals of a complex the composition of which is still unknown.

Thesis (Ph. D.) in Chemistry--University of Maine, 2003. / Includes vita. Includes bibliographical references (leaves 181-196).

No description available.

Different metals and metal complexes have been used as catalysts in many industries such as commodity petrochemicals, fine and specialty chemicals, polymers, environmental services, agrochemicals and pharmaceuticals. Although these catalysts allow for increased reaction rates and selectivity, they can also be toxic, expensive and of limited supply (cf. Pt group metals). This has led researchers to the intensive study of first row metal catalysts, with nickel standing out as the most widely studied to date. As found for other first row metal catalysts, nickel’s easy access to oxidation states 0-3 allows for a number of different one- and two-electron mechanisms and novel transformations. In Chapter 2 we use a phosphine-free, tridentate N,N,N ligand to generate an active catalyst for the C-N cross-coupling reaction of aryl halides with amines. The catalyst demonstrated excellent turnover numbers (up to 484) for the amination reactions that are proposed to proceed through a Ni(I)-Ni(III) cycle. In Chapter 3 we investigate the Ni coordination chemistry of a biomimetic SNS thiolate ligand. Protonation of the Ni bis(thiolate) complex, Ni(-SNS)2, removes one SNS ligand, affording crystals of a thiolate-bridged dimer dication, {[Ni(--SNS)]2}2+ that exhibits unique anionic tridentate ligand dynamics. Dissolving these crystals, even in weakly-coordinating solvents such as dichloromethane, gives a mixture of ‘naked’ Ni2+ and paramagnetic, trinuclear {[Ni(--SNS)2]2Ni}2+. Although this equilibrium lies far to the right (no diamagnetic dication visible in NMR), addition of ancillary ligands proceeds smoothly to provide several mono- and dinuclear Ni thiolate products, [Ni-SNS)L]n – potential bifunctional catalysts for further studies. In Chapter 4 we demonstrate using chemical and electrochemical techniques that one-electron reduction of Ni(-SNS)2 triggers quantitative imine C-C bond coupling, forming [Ni(S2N2)]- with a redox-active ligand. Spectroelectrochemical studies indicated reversible oxidation and reduction steps give three stable redox states, ([Ni(S2N2)]0/-/2-), that were characterized by NMR, EPR and UV-Vis spectroscopy, X-ray diffraction and computational chemistry. While the Ni(0) dianion (and not the Ni(I) anion) reacted reversibly with phenol and carbon dioxide, results from Chapter 5 showed that reactions with strong electron-acceptor fluoroalkenes proceeded more cleanly with the Ni(I) anion. The latter reactions afforded a mixture of fluoroalkenyl and fluoroalkyl products resulting from C-F bond activation and electron transfer/H atom abstraction, respectively. In Chapter 6 we discuss our results in the context of the current state of the art and suggest some avenues for future development.

This theses presents the synthesis and characterization of Cd(II)-, Pb(II)- and Hg(II)-aminoethanethiolates in aqueous media. 2-Aminoethanethiolate, a versatile sulfur andnitrogen (S/N) based ligand was used due to its resemblance to the naturally occurringamino acid, cysteine. The work is presented in four major parts: first, backgroundinformation on the versatile structural chemistry of Cd, Pb and Hg-thiolates with S/Ncontaining ligands; second, synthesis and characterization of Cd(II) with 2-aminoethanethiolates; third, synthesis and characterization and structural chemistry ofPb(II) with 2-aminoethanethiolates; and fourth, synthesis and characterization of Hg(II)-2-aminoethanethiolates in solution- and solid-state with emphasis on the mechanisticpathways for the formation of clusters.The compounds reported here are synthesized by direct addition of the metal saltsand the ligand in deionized water. For Cd(II)-thiolates, insoluble products (77 - 80 and 82- 84) due to the formation of oligomers and polymers were obtained. In Pb(II)-thiolates(85 - 89), the structural chemistry is variable due to the extensive array of coordinationenvironments Pb can acquire. This can be related to the stoichiometry of the reaction aswell as the reaction conditions. The structural trends in Cd(II)- and Pb(II)-thiolates arenot observed in the Hg(II)-thiolates. Rather the halide influences the formation ofmolecular as well as non-molecular structures. Systematic pathways for the formation ofthe compounds based on a variety of commonly observed structural 'building blocks' arepresented. For Cl, Br derivatives, a four-coordinate intermediate, [Hg(SR)2X2] (88 - 96)and for I derivatives three-coordinate intermediates, [HgI(SR)2] and [HgI2(SR)] (97 -100) can be considered as building units. The compounds were characterized withIR/Raman, NMR, MS, Uv-Vis and X-ray crystallography.

Les nanoparticules d'or de petite taille (< 5 nm) sont des matériaux qui présentent une bonne activité catalytique dans des réactions d'oxydation, et ce dans des conditions relativement douces. Cependant, il est difficile d'obtenir des nanoparticules monodisperses et de taille inférieure à 5 nm. En ce sens, les clusters d'or sont intéressants, car ce sont des composés atomiquement définis avec une formulation propre. Cela signifie que dans un cluster, le nombre d'atomes d'or et de ligands le stabilisant est déterminé. Comme ils peuvent être isolés purs, ils constituent donc une classe de nanoparticules parfaitement monodisperses. Nous nous sommes intéressés, dans le cadre de cette thèse, à la synthèse de clusters d'or et à leur assemblage afin d'avoir des catalyseurs atomiquement définis. Les nanoparticules d'or sont souvent utilisées après dépôt sur un support, résultant en la perte de surface accessible. Nous voulons donc utiliser ces clusters (i) comme espèces moléculaires déposées sur un support et (ii) comme briques moléculaires pour l'assemblage de réseaux tridimensionnels où la porosité permettrait la diffusion des réactifs/produits pour s'affranchir des effets de supports. Notre étude porte donc sur la synthèse de clusters d'or et nous nous sommes également intéressés aux polymères de coordination d'or (I), un intermédiaire de réaction important dans la synthèse de clusters et à ses propriétés photophysiques. Afin d'avoir des clusters avec une fonction externe permettant de les assembler ou de les déposer sur un support, nous avons développé une nouvelle voie de synthèse de clusters stabilisés par des ligands de type thiophénolates para-substitués. Nous avons ainsi isolé de nouveaux clusters stabilisés par des ligands hétérotopiques comme [Au25(SPh-pNH2)17]. Ces composés ont ensuite été déposés sur un support mésoporeux (SBA-15) et utilisés comme catalyseurs dans différentes réactions d'oxydation. Nos résultats montrent que les clusters d'or sont donc des précurseurs moléculaires permettant de préparer des catalyseurs efficaces, ayant une petite taille de particules (1-2 nm) et présentant des activités catalytiques très élevées comparativement aux matériaux de référence / Small gold nanoparticles (< 5 nm) are materials presenting a good catalytic activity in oxidations reactions, especially under soft conditions of temperature and pressure. However, it can be difficult to obtain monodisperse particles with a diameter less than 5 nm. In this sense, gold clusters are interesting, because they are atomically defined compounds, presenting a proper formulation. This means that the number of gold atoms and of stabilizers in the clusters are defined and, as they can be isolated pure, they constitue a novel class of perfectly monodisperse nanomaterials. Therefore, we are interested, in this thesis, in the synthesis and assembly of gold clusters. Indeed, gold nanoparticles are usually deposited on a support, resulting in the loss of accessible area. We therefore wanted to use gold clusters as (i) molecular species deposited on a support and (ii) as building blocks to assemble and organize tridimensional networks where the porosity permits the substrates/products diffusions and avoid the support effects. Our study deals with the synthesis of gold clusters, and we are also interested in the gold (I) coordination polymers, which are important reaction intermediates formed during the clusters synthesis and to its photophysical properties. In order to have clusters presenting external functions enabling their assembly or deposition on a support, we developed a novel synthesis suitable for para-substituted thiophenolates. We managed to isolate new clusters stabilized by heterotopic ligands such as [Au25(SPh-pNH2)17]. Those compounds have been deposited on a mesoporous support and used as oxidative catalysts. Our results show that gold clusters are molecular precursors that permit to prepare effective catalysts with narrow particle size (1-2 nm) and presenting high catalytic activity compared to the one exhibited by reference materials

Ce projet concerne la synthèse et caractérisation de nouveaux matériaux composites à base de nanoclusteurs de thiolates d’or Au25(SR)18 (tGNCs), supportés sur divers polymères de coordination (MOFs), ainsi que sur ZrO2. L’activité catalytique de ces matériaux a été évaluée sur la transformation de différents substrats. Les tGNCs sont des matériaux atomiquement bien définis et connus pour être actifs dans des réactions d’oxydation. Les nanoparticules de MOFs sont des matériaux pouvant servir de support pour des tGNCs avec de bonnes dispersions. Certains MOFs sont connus pour avoir des propriétés acides et peuvent être actifs en catalyse. Parmi eux, MIL-101 (Cr), UiO-66 (Zr) et ZIF-8 (Zn) on été choisis en raison de leur propriétés acides et/ou de stabilité thermique. La synergie entre les tGNCs et les MOFs a été évaluée à travers la conversion catalytique de différents substrats tels le glucose, le fructose, l’alcool benzylique et le furfural, impliquant des étapes nécessitant un caractère acide et/ou oxydant. Globalement, il n’a pas été observé d’impact de la présence d’or sur la réactivité de ces substrats, et les tendences catalytiques sont celles obtenues avec les MOFs seuls. Cela est certainement dû à la stabilité thermique non suffisante des MOFs qui prévient une calcination efficace des tNGCs. Lorsque ces clusters sont déposés sur ZrO2, il a été possible de les calciner à différentes températures pour étudier l’effet du ligand et de la taille de particules, pour des réactions d’oxydation en phase liquide. Ainsi, il a été montré par exemple que la température de calcination a un impact significatif sur le comportement catalytique de ces composites, qui ont donné de bonnes activités pour l’oxydation de l’alcool benzylique en benzaldéhyde dans le toluène et en conditions douces, et pour l’esterification oxydante du furfural en furoate de méthyle / This research project reports the synthesis and characterization of new composite materials based on Au25(SR)18 thiolate gold nanoclusters (tGNCs), supported over a range of metal organic frameworks (MOFs), and ZrO2. The synthesized composite materials were tested for catalytic transformations of various substrates. tGNCs are atomically well defined materials known to be active in oxidation reactions. MOFs nanoparticles are materials suitable for high dispersion of tGNCs. Some MOFs are known to have acidity and can be active as catalysts. Among them, MIL-101 (Cr), UiO-66 (Zr) and ZIF-8 (Zn) were chosen due to their acidic and/or thermal stability properties. The synergy between tGNCs and MOFs has been tested through catalytic conversions of different substrates like glucose, fructose, benzylalcohol and furfural, involving steps requiring acidic and oxidative features. Globally, no impact of the presence of Au clusters was observed, and the composite materials showed the same catalytic trends as those obtained with the MOFs alone. This is mainly due to the not sufficient thermal stability of the MOFs that prevents efficient calcination of the tGNCs. In contrast, when deposited on ZrO2 it was possible to calcine Au25(SG)18 nanoclusters at different temperatures to study the ligand and particle size effects in liquid phase oxidation reactions. For example, the calcination temperature had a significant impact on the catalytic behaviour of this composite materials, which showed good activity for the oxidation of benzyl alcohol into benzaldehyde in toluene under mild conditions, and of furfural oxidative esterification into methyl-2-furoate

Controlled synthesis of functional nanostructures is of paramount interest due to their novel properties and efficient functionalities. The size and morphology of each particle in the nanoscale contribute to their optical and electronic properties. Also, the collective arrangement of these nanostructures in 3D space maximizes active sites available for the cost-effective catalysis. Recent advances in the field show a vast range of nanostructures with unique designs that affect their catalytic properties. In this dissertation, utilizing silver halides as a unique platform to develop high-performance catalysts were discussed with their respective synthesis strategies, structural evolution, and structure-related properties. Initially, we synthesized well-defined silver chlorobromide (AgCl0.5Br0.5) nanostructures investigating the effects of various reaction parameters on the synthesis. Simple reaction parameters were overlooked to gain additional controllability on determining the morphology of the nanocrystals regardless of the composition. Thus, the influence of the size and exposed surface facets was investigated towards photocatalytic activity performing methylene blue degradation on AgCl0.5Br0.5 with different sizes and morphologies, under visible light. Then, the ability to use these AgCl0.5Br0.5 nanocubes were investigated as a reactive and sacrificial template for the synthesis of nanoplates and nanoshells. As an example, fast precipitation reaction between Ag+ and benzenethiol (BT–) results in an uncontrollable growth leading to aggregated structures. The low solubility and the planer surfaces of the silver halide cubes were utilized to reduce the reaction rate and promote the growth of layered AgBT as plates, which can be organized into hollow nanostructures. Time-dependent microscopic and spectroscopic measurements showed the structural evolution and associated kinetics of the conversions. Developing a comprehensive understanding enabled generalizing the procedure to synthesize other silver-based hollow nanostructures. Mechanistic studies showed two different hollowing mechanisms involving, that depends on the anion being exchanged. The degree of nucleation and the crystal structure of silver-sulfur compounds determined the relative diffusion of ions leading to their overall size and morphology. The hollow morphology was shown to have higher stability with a large surface area relative to its aggregated solid counterpart. Next, highly porous Ag nanostructures were synthesized electrochemically, using silver thiolate nanocages. High porosity and their arrangement as plates enhanced available active sites and mass transport for CO2 electroreduction. Furthermore, the strategy was extended to design bimetallic nanostructures with enhanced bimetallic boundaries where selectivity of ethanol formation from CO2 electroreduction can be increased. Overall, the study explores the novel approaches to utilize chemical and physical properties of silver halides for various material designs that determines their enhanced performance. / Chemistry

Small molecule Zn(II) complexes containing N- and S- donor environments may serve as appropriate models for mimicking Zn protein sites, and thus, their reactions with heavy metal ions such as Pt(II) and W(0) may provide insight into possible adduct formation and zinc displacement. To study such possible interactions between zinc finger proteins and platinum-bound DNA, the ZnN2S2 dimeric complex, N,N?-bis(2- mercaptoethyl)-1,4-diazacycloheptane zinc (II), [Zn-1?]2, has been examined for Znbound thiolate reactivity in the presence of Pt(II) nitrogen ? rich compounds. The reactions yielded Zn/Pt di- and tri- nuclear thiolate-bridged adducts and metalexchanged products, which were initially observed via ESI-mass spectrometry (ESI-MS) analysis of reaction solutions, and ultimately verified by comparison to the ESI-MS analysis, 195Pt NMR spectroscopy, and X-ray crystallography of directly synthesized complexes. The isolation of Zn-(?-SR)-Pt-bridged [(Zn(bme-dach)Cl)(Pt(dien))]Cl adduct from these studies is, to our knowledge, the first Zn-Pt bimetallic thiolatebridged model demonstrating the interaction between Zn-bound thiolates and Pt(II). Additional derivatives involving Pd(II) and Au(III) have been explored to parallel the experiments executed with Pt(II). The [Zn-1?]2 was then modified by cleavage with Na+[ICH2CO2]- to produce (N- (3-Thiabutyl)-N?-(3-thiapentaneoate)-1,4-diazacycloheptane) zinc(II), Zn-1?-Ac or ZnN2SS?O, and 1,4-diazacycloheptane-1,4-diylbis(3-thiapentanoato) zinc(II), Zn-1?-Ac2 or ZnN2S?2O2, monomeric complexes (where S = thiolate, S? = thioether). The [Zn-1?]2 di- and Zn-1?-Ac mono-thiolato complexes demonstrated reactivity towards labile-ligand tungsten carbonyl species, (THF)W(CO)5 and (pip)2W(CO)4, to yield, respectively, the [(Zn-1?-Cl)W(CO)4]- complex and the [(Zn-1?-Ac)W(CO)5]x coordination polymer. With the aid of CO ligands for IR spectral monitoring, the products were isolated and characterized spectroscopically, as well as by X-ray diffraction and elemental analysis. To examine the potential for zinc complexes (or zinc-templated ligands) to possibly serve as a toxic metal remediation agents, Zn-1?-Ac and Zn-1?-Ac2 were reacted with Ni(BF4)2. The formation of Zn/Ni exchanged products confirmed the capability of ?free? Ni(II) to displace Zn(II) within the N-, S-, and O- chelate environment. The Zn/Ni exchanged complexes were analyzed by ESI-MS, UV-visible spectroscopy, IR spectroscopy of the acetate regions, and X-ray crystallography. They serve as foundation molecules for more noxious metal exchange / zinc displacement products.