Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Douglass F. Taber, Dept. of Chemistry and Biochemistry. Includes bibliographical references.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, August 1999. / Includes bibliographical references. Also available on the Internet.

Thesis (PhD)--University of Stellenbosch, 2005. / Bibliography. Also available via the Internet.

Thesis (MSc)--University of Stellenbosch, 2005. / Bibliography. Also available via the Internet.

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.

Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch,2005. / This study comprises the preparation and full characterisation of new carbene complexes of group 10 metals (Ni, Pd or Pt), the group 9 metal, rhodium, as well as group 6 metals (Cr and/or W). N-heterocyclic carbene (NHC) complexes of nickel and palladium were prepared via oxidative addition of the corresponding carbene precursors imidazolium-, imidazolinium-, pyridinium- and quinolinium chloride salts, to M(PPh3)4 (M = Ni or Pd). Three types of carbene complexes, namely the standard five-membered two-N carbene complexes, new six-membered NHC complexes and novel six-membered rNHC complexes received attention. In the rNHC complexes the heteroatom (N) is removed from the carbene carbon. These new square planar carbene complexes of the general formula trans-[(PPh3)2MCl(L)]X (M = Ni or Pd; X = BF4 or PF6) L = 1,3-dimethyl-2,3-dihydro-1Himidazol- 2-ylidene, 1,3-dimethyl-2,3,4,5-tetrahydro-1H-imidazol-2-ylidene, 1-methyl-1,2-dihydropyridin- 2-ylidene, 1-methyl-1,2-dihydro-quinolin-2-ylidene, 1,4-dimethyl-1,2-dihydro-quinolin-2- ylidene, 2-methoxy-1-methyl-1,4-dihydro-quinolin-4-ylidene, 1-methyl-1,4-dihydro-pyridin-4- ylidene) have been isolated and characterised. The preparation of the corresponding carbene complexes of platinum was complicated by the formation of [PtCl(PPh3)3]BF4 and the desired carbene complexes could not be isolated in pure form. The investigation of rNHC complexes was extended to include the synthesis of (CO)5M{CSC(CNCMe2CH2O)CHCH} (M = Cr and W). The molecular and crystal structures of thirteen of the new carbene complexes including the structures of both cis- (only formed below –20°C) and trans-chloro(1-methyl-1,2-dihydro-quinolin- 2-ylidene)bis(triphenylphosphine)palladium(II) tetrafluoroborate were determined. The metalcarbene bond distances in both the palladium and nickel carbene families do not differ significantly. The carbene ligands can be arranged in a series of increasing trans-influence, using the metalchloride bond distance as a guideline, as follows: 1,3-dimethyl-2,3-dihydro-1H-imidazol-2-ylidene and 1,3-dimethyl-2,3,4,5-tetrahydro-1H-imidazol-2-ylidene < 1-methyl-1,2-dihydro-pyridin-2- ylidene < 2-methoxy-1-methyl-1,4-dihydro-quinolin-4-ylidene, 1-methyl-1,4-dihydro-pyridin-4- ylidene. The crystal and molecular structures of two platinum compounds, cis-chloro(2-methoxy-1- methyl-1,4-dihydro-quinolin-4-ylidene)bis(triphenylphosphine)platinum(II) tetrafluoroborate and the byproduct [PtCl(PPh3)3]BF4 were also determined. Trans-chloro(2-methoxy-1-methyl-1,4-dihydro-quinolin-4-ylidene)bis(triphenylphosphine) palladium(II) tetrafluoroborate was found to be a very active catalyst, compared to simpler palladium carbene and phosphine complexes, in the Mizoroki-Heck and Suzuki-Miyaura coupling reactions. Quantum mechanical calculations indicated that the rNHC ligand in this complex is bound stronger to the palladium than a standard imidazole-derived NHC ligand. Further calculations suggested that the remote heteroatom carbene (rNHC) complexes of nickel(II) are significantly more stable when compared to the normal carbene (NHC) complexes. Energy decomposition analysis suggested that the rNHC ligands are strong s-donors and weak -acceptors. Unsymmetrical imidazolium-derived bis(carbene) complexes, [Rh(NHC)2COD]Br, bromomono( carbene) complexes, Rh(Br)COD(NHC), and chloro-mono(carbene) complexes, Rh(Cl)COD(NHC) where NHC = 1-R-3-methyl-2,3-dihydro-1H-imidazol-2-ylidene (R = ethyl, propyl or butyl), were formed in each reaction of the corresponding free carbene ligand with [Rh(Cl)COD]2. [Rh(Br)COD(NHC)] formed as a result of substitution of a chloride ligand by a Br-- anion. The carbonyl complexes, cis-[Rh(CO)2X(NHC)] (X = Br or Cl; NHC = 1-ethyl-3-methyl- 2,3-dihydro-1H-imidazol-2-ylidene) were isolated after the substitution of the COD ligand in Rh(X)COD(NHC) (X = Br or Cl) with CO. Isomerisation of these cis-carbonyl complexes to the trans isomers was observed. Cis-[(h4-1,5-cyclooctadiene)bis(1-butyl-3-methyl-2,3-dihydro-1H-imidazol-2-ylidene)rhodium(I)] bromide, bromo(h4-1,5-cyclooctadiene)(1-methyl-3-propyl-2,3-dihydro-1H-imidazol-2-ylidene) rhodium(I) and cis-[(h4-1,5-cyclooctadiene)bis(1-butyl-3-methyl-2,3-dihydro-1H-imidazol-2- ylidene)rhodium(I)]bromide were also characterised by single crystal X-ray diffraction. The synthesis and structural characterisation of a series of acyclic and heterometallacyclic Fischertype carbene complexes in which a soft donor atom (P) attached to the carbene side chain is either uncoordinated, (CO)5M=C(NMe2)CH2PPh2 (M = Cr or W), bonded to the original central metals (Cr or W) in four-membered chelates, (CO)4M=C(NMe2)CH2PPh2, or coordinated to a second M(CO)5 unit (only isolated for chromium) (CO)5Cr=C(NMe2)CH2P(Ph2)Cr(CO)5, were carried out. These compounds were produced by the reaction of the anionic Fischer-type aminocarbene complexes, [(CO)5Cr=C(NMe2)CH2]Li (M = Cr or W), with ClPPh2. The formation of the four-membered chelates, via cyclisation, occurs much faster for Cr than for W. The aminocarbene-phosphine chelates represent the first examples of structurally characterised, four-membered C,P-chelate carbene complexes.

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Please refer to fulltext for abstract. / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISCH ABSTRACT: Please refer to fulltext for abstract / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

The reactions of five trihalomethyl group substituted electron-deficient olefins with electron-rich olefins were studied in order to determine the effect of steric bulk upon the subsequent reactions of the tetramethylene intermediates initially formed. Reactions of β-trihalomethyl group substituted olefins yielded cyclobutane adducts, resulting from a gem dimethyl effect which accelerates the collapse of the tetramethylene intermediate. Reactions of α-trihalomethyl group substituted olefins gave both small molecule and polymeric products. Polymers were produced in reactions where steric interactions between the termini of the tetramethylene intermediates prevented ring formation. Ester substituted electron-deficient olefins reacted with electron-rich olefins to give both cyclobutane and 6-alkoxy-3,4-dihydro-2H-pyran derivatives. A transition from concerted to stepwise reaction was observed, resulting from steric hindrance in the transition state leading to [4+2] cycloaddition. Exploratory studies of ion-radical propagation and chain transfer in polymerization processes were also conducted. The acid catalyzed free radical polymerization of imines was attempted, along with chain transfer studies of zwitterion-radical intermediates.