Thermolysis of Cp*W(NO)(CH₂CMe₃)₂ (2.1) in halo, methoxy, or phenylethynyl-substituted benzenes leads to the formation of the alkylidene intermediateCp*W(NO)(=CHCMe₃) which selectively activates ortho C-H bonds of the organicsubstrates. The ortho-regioselectivity diminishes as the size of the substituent increasesfrom F (97 %) to C-=CPh (51 %). In the solid-state structure of all complexes the ortho-substituent is not coordinated to the metal centre; rather, the metal centre is engaged inagostic interactions with a neopentyl methylene C-H bond. Mechanistic studies on the chlorobenzene reaction reveal that the ortho-C-H-activation product is preferentially formed via thermal isomerization from the meta / para-C-H-activation isomers. Reactions between Cp*W(NO)(CH₂EMe₃)Cl (E = C or Si) and a variety of bis(allyl)magnesium reagents lead to the expected formation of Cp*W(NO)(alkyl)(allyl)complexes. Cp*W(N0)(CH₂CMe₃)(η³-CH₂CHCH₂) (3.5), Cp*W(N0)(CH₂CMe₃)(η³-CH₂CMeCH₂) (3.6), Cp*W(N0)(CH₂CMe₃)(η³-CH₂CHCHMe) (3.7),Cp*W(N0)(CH₂CMe₃)(η³-CH₂CHCHPh) (3.8) and Cp*W(N0)(CH₂SiMe₃)(η³-CH₂CHCHMe) (3.9) have thus been synthesized in moderate yields. The solid-state molecular structures of 3.5 and 3.7-3.9 feature a σ-π distorted ally! ligand in the endoconformation. Complex 3.5 reacts with pyrrolidine at RT to form Cp*W(NO)(NC₄H8)(CHMeCH₂NC₄H8) (3.10), a nucleophilic-attack product. Complexes 3.6-3.9 effect the concurrent N-H and α-C-H activation of pyrrolidine at RT and form alkyl-amido complexes analogous to the previously known Cp*W(N0)(CH₂EMe)(NC₄H₇-2-CMe₂CH=CH₂) (3.12). Thermolysis of Cp*W(N0)(CH₂CMe₃)(η³-CH₂CHCHMe) (3.7) at RT leads to the loss of neopentane and the formation of the η²-diene intermediate Cp*W(N0)(η²-CH₂=CHCH=CH₂) (A) which has been isolated as a PMe₃ adduct. In the presence of saturated organic substrates, C-H activation occurs exclusively at the methyl positions of the molecule. Reactions between intermediate A and unsaturated substrates lead to coupling between the coordinated η²-diene and the unsaturation on the organic molecule.Treatment of Cp*W(N0)(n-C₅H₁₁)(η³-CH₂CHCHMe) (4.1) with I₂ at -60 °C produces n-C₅H₁₁ I in moderate yields. Thermolysis of Cp*W(N0)(CH₂CMe₃)(η³-CH₂CHCHPh) (3.8) in benzene at 75 °C for one day leads to the exclusive formation of Cp*W(N0)(H)(η³-PhCHCHCHPh) (5.1).Trapping, labelling, and monitoring experiments suggest that 5.1 is formed via 1) the loss of neopentane and the generation of the allene intermediate Cp*W(N0)(η²-CH₂=C=CHPh), 2) the C-H activation of benzene resulting in a phenyl phenylallyl complex, and 3) the thermal isomerization of this latter species to 5.1.

No description available.

Thesis (M.S.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (Ph.D.(Chemistry))--University of Pretoria, 2003. / Includes bibliographical references.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references. Also available in electronic version.

No description available.

This study focussed on two copper(II)-containing metal-organic frameworks (MOFs): Cu2Na(OH)B4C•7H2O and Cu2¼(OH)½B4C•8H2O (B4C = 1,2,4,5- benzenetetracarboxylate). They are both covalent, three-dimensional metalorganic framework polymers containing voids filled with water molecules. Both were characterised by elemental analysis, infrared spectroscopy, X-ray powder diffractometry (both in situ and regular), thermogravimetric analysis, differential scanning calorimetry and X-ray photoelectron spectroscopy. These two MOFs are essentially identical, with the only difference being the substitution of sodium by copper at every 4th site (disordered throughout the crystal). The guest inclusion properties of both MOFs were studied and compared. Although both structures collapse on dehydration, it was observed that Cu2Na(OH)B4C•7H2O is able to take up signifcant amounts of water, methanol and ethanol. All these processes are fully reversible. Car-Parrinello molecular dynamics studies suggest that it is a strong interaction between the oxygen atoms on these molecules with the sodium cation of the MOF that is responsible for this signifcant uptake. In contrast, Cu2¼ (OH)½ B4C•8H2O, the MOF without a sodium cation, did not demonstrate any methanol or ethanol uptake, but was able to take up some water. The uptake of water, however, is not a fully reversible process. The absence of sodium likely results in insuffcient energy to draw methanol and ethanol into the framework, while a subtle rotation of a carboxylate group on dehydration decreases the ability of the framework to form hydrogen bonds, thus reducing the ability to take up water. A series of hydrothermal syntheses were performed in order to develop a method of synthesis superior to the current gel-based synthesis that requires several months and has poor yields. The hydrothermal products were characterized by elemental analysis, infrared spectroscopy, X-ray powder diffractometry, thermogravimetric analysis and differential scanning calorimetry. It was shown that the MOF Cu2Na(OH)B4C•7H2O may be synthesised in almost 100% yield by using a temperature of 120°C over a period of 72 hours. It was not possible to synthesise Cu2¼ (OH)½ B4C•8H2O in a 100% yield - it was only obtained as a minor product.

M.Sc. / This study focussed on two areas of research in the field of organometallic chemistry. The first entails the preparation and characterisation of a number of Fischer-type carbene complexes of the general formula (C0) 5M(OR)(RI) (1 - 4). For the first group M = Cr, Mo or W, R = Et or Me and re = Ph or BiPh. A second, somewhat different group was prepared by deprotonating 4- methylthiazol-2-methyltlfioether, reacting it with M(CO) 6, where M = Cr or W, and neutralising the resulting anion with methyltriflate. Both metals afforded only one product which could be successfully purified and characterised as M(C0),{C(OCH3)(C=C(CH3)N=C(SCH3)S) (6,7). The crystal structure of the tungsten complex was solved by single crystal X-ray techniques. A similar carbene complex preparation was carried out with 5-methylthiophenilyl-2-thiomethylether and M(C0)6, M = Cr or W, as starting reagents. In addition to the expected carbene complexes M(CO)5 (C(OCH3)(CH2SHCH=C(CH3)S)), M = Cr and W (9a, 10a), deprotonation of a ring carbon yielded M(C0) 5{C(OCH3)(6=C(SCH3)SC(CH3)=CH)) M = Cr and W (9b, 10b), whereas unreacted starting material afforded the sulfide W(C0) 54-SC(SCH3)=CHCH=C(CH3) (11). The second part of the thesis describes the preparation of pentacarbonyl thione and iminocomplexes, as well as tricarbonyl imino-, sulphide and dinuclear re-sulphide complexes. 4- Methylthiazoly1-2-thiolate were used for nucleophilic attack on (C0) 5Cr--C(OR)(12. 1) (1 and 4) to yield the thione complex Cr(C0) 54-S=CN(CH3)C(CH3)=CHS (13) upon methylation. Two other products were also obtained from these reactions : Cr(C0) 54-NC=CHSCH=C(CH3) (12) and Cr(CO) 54-N=C(CH3)SCH=C(CH3) (14), which indicates incomplete reaction with sulfur during the formation of the mentioned thiolate. Three beautiful electron ligand systems were produced by reacting 4-methylthiazol-2-disulphide with (CO),W(THF) or Fe2(C0)) . A new "butterfly" bidentately coordinated tricarbonyl tungsten complex, [(C0)3 1/{N(S)SCH(CH3)) 2] (16) was obtained. The crystal structure of this complex shows many similarities to a known complex, (C0)3W(n2-PyS)2 that was prepared from ionic metalcarbonyl precursors. In addition to 16, a thione complex W(C0) 54-SHC(CIi )=CHS (17) also formed from the reaction with (CO) 5M(THF). The reaction between (CO),M(THF) and 4-methylthiazolyi-2-disulphide thus probably involves heterolytic bond cleavage and protonation on the silica gel. The reaction of Fe 2(CO)9 with the same disulphide resulted in the formation of the dinuclear compound Fe2(C0)6(SC=NC(CH3)=CHS)2 (18), possibly via the homolytic splitting of the disulphide bond. The crystal structure of this compound revealed the Fe-Fe-bond and eclipsed configuration, typical of this type of Fe-cluster complex. Finally, two thione complexesM(C0)54—S(SMe)(eHCH(Me)S), (M= Cr and W; 20,21) were found to isomerise in solution to their sulphide analogues of which only the chromium complex Cr(C0)54— SC(Me)=CHCH=C(C(=S)(SMe)) (22) could be characterised.

Olefin metathesis is a powerful tool for assembly of carbon-carbon bonds. Amines and related N-donors are problematic functional groups in Ru-catalyzed olefin metathesis - a well- documented, but poorly understood problem. The first part of this thesis focuses on amine-induced deactivation pathways; two of which are described in depth. Alkylidene abstraction, a previously unknown reaction for nitrogen nucleophiles, was observed for smaller and less Bronsted-basic amines. Deprotonation of the metallacyclobutane intermediate formed during catalysis is prominent for highly Bronsted basic or sterically bulky N-donors. Monosubstituted (and, by extension unsubstituted) metallacyclobutanes are particularly vulnerable to deprotonation. For each pathway, the fate of the alkylidene Ru=CHR functional group proved key in determining the nature of deactivation. Both pathways have been detected during catalysis, as evidenced by formation of diagnostic amine (RCH2NR2’) or substituted propene products. A combination of quantitative NMR and GC-MS analysis was used to identify these species on loss of the Ru-alkylidene functional group. The second part of this thesis focuses on incorporating amines into catalyst design – an under-utilized strategy in the context of Ru-catalyzed olefin metathesis. A modified Grubbs-type catalyst was developed featuring a bulky, relatively non-basic biaryldiamine ligand. Metathesis activity for this catalyst was comparable, and in some cases superior to the most widely-used homogeneous catalysts currently available. Several new, related Ru-benzylidenes were also prepared and fully characterized in conjunction with the mechanistic studies described above. Progress toward development of N-anion-containing metathesis catalysts is also discussed. Synthesis of Ru-hydride complexes originally intended for this purpose allowed for a fundamental study of the coordination chemistry and reductive elimination chemistry of the NPh2– anion.

The principle aims of this thesis have been to develop well-defined heterogeneous catalysts for potential applications in tandem hydrocarbon upgrading. Catalysts for olefin oligomerisation and metathesis of &alpsha;-olefins and transfer hydrogenation of alkanes based on tungsten mono-imido and PCP pincer iridium complexes have been synthesised and immobilised on solid supports. The reactivity of the immobilised catalysts has been tested and compared with the precursor complexes. Co-immobilisation of the two complexes on the same support has been undertaken. <b>Chapter One</b> provides a background to the olefin metathesis reaction and the development of highly active tungsten mono-imido and ruthenium alkylidene complexes. A summary of the implementation of the olefin oligomerisation reaction by industry and the development of highly active systems based on group 6 metals is discussed, along with a mechanistic discussion. The SOMC grafting procedure is considered and the immobilisation of catalysts for alkane and olefin metathesis and oligomerisation discussed; with focus on support materials: silica, sMAO and AMO-LDHs. Finally, tandem catalysis and its use in hydrocarbon upgrading and copolymerisation are presented. <b>Chapter Two</b> details the synthesis of W(NR)Cl₄(THF) complexes and their conversion to W(NR)Me₃Cl complexes employing TMA. The products are characterised by single crystal X-ray diffraction, NMR and FTIR spectroscopy. W(NR)Me₃Cl complexes are shown to be active for the selective dimerisation of ethylene to 1-butene. Attempted formation of possible intermediates in the reaction is presented, and efforts to form mimics for silica supported species are also discussed. <b>Chapter Three</b> describes the preparation of AMO-LDHs for use as catalyst supports. The effect on the surface hydroxyl content and structural properties of these materials by thermally treating them under vacuum is analysed. Their capability to act as supports for ethylene polymerisation after impregnation with MAO and (ⁿBuCp)₂ZrCl₂ is described. <b>Chapter Four</b> investigates the immobilisation and characterisation of synthesised tungsten mono-imido complexes on sMAO, AMO-LDHs and silica, utilising SSNMR, FTIR and X-ray absorption spectroscopy. The reactivity of the grafted complexes towards ethylene oligomerisation is discussed. For the immobilised species effects of varying the imido ligand, temperature and solvent medium are reported. Attempts to immobilise ruthenium carbene complexes on AMO-LDHs and sMAO is detailed. <b>Chapter Five</b> gives an account of the immobilisation of Ir(^tBuPCP)HCl on sMAO which is characterised by SSNMR and FTIR spectroscopy. Molecular analogues of the supported species are synthesised and reactivity for the hydrogenation of ethylene compared. Transfer hydrogenation reaction with sMAO-Ir(^tBuPCP)HCl and COA or ethane with TBE as a sacrificial H₂ acceptor are discussed. Finally, co-immobilisation of W{N(2,6-F-C₆H₃)}Cl₄(THF) and Ir(^tBuPCP)HCl on sMAO was carried out and the solid characterised by SSNMR spectroscopy. <b>Chapter Six</b> provides experimental details and characterising data for the preceding chapters. An <b>Appendices</b> with crystallographic data, and characterising spectra for each chapter is provided, while the <b>Electronic Appendix</b> contains a combined CIF and checkcif for all the molecular structures presented.