The large number of new heteronuclear bidentate ligands recently reported in the literature has unveiled a new area of research, namely that the use of different heteroatoms in bidentate ligands has led to new avenues towards more selective processes especially in asymmetric transformations. Instead of employing the traditionally used bidentate bisphosphine ligands, the dual objective of this study was therefore to design and synthesise P-N based bidentate ligands, and to apply these in catalytic transformations. A general route towards the synthesis of different series of P-N based ligands was followed. This path involved, as initial step, the condensation of o-diphenylphosphinobenzaldehyde with a series of primary amines to afford a series of iminophosphine ligands. Upon subsequent reduction of the iminophosphine ligands, a series of secondary aminophosphine analogues was obtained, and upon alkylation of the latter in the presence of a base, their tertiary aminophosphine derivatives were isolated. In these three series of ligands, the oxidation state of the nitrogen atom, as well as the degree of alkylation on this atom, was varied. These ligands were further elaborated by the incorporation of a second phosphorus atom to the already bidentate P-N ligands. This was achieved by reacting the secondary aminophosphine ligands with a base and chloro-diphenylphosphine. In order to vary the electronic nature of the newly introduced second phosphorus atom, a method for the incorporation of a dicyclohexyl phosphine moiety was developed. By introducing this group into the P-N backbone of these ligands, it was thus possible to electronically distinguish between two different phosphorus atoms in one ligand. Apart from the nature of the nitrogen and phosphorus atoms in these ligands, the use of different R-groups derived from the primary amines, enabled further variance in the inherent characteristics of these ligands: the variation in R-groups included aliphatic moieties, aromatic groups, and groups that contained additional heteroatoms. In these cases, the variation in R-groups thus also influenced the denticity of these ligands, which could render them more versatile in catalytic applications. In addition, a series of S-N based ligands, as well as some chiral P-N based ligands, was synthesised by using the previously-developed protocol. The oxygen sensitive nature of phosphines sometimes requires protection of these phosphines during different synthetic steps, and borane is often used for this purpose. However, deprotection of these phosphine ligands is required before they can be used in metal-catalysed reactions. As an adjunct to the present synthetic strategy, the concept of deprotecting phosphine-borane complexes such that new, extractable borane complexes are formed, was investigated, and formed a small part of this overall study. The deprotection of phosphine-boranes was performed using various “new” deprotecting reagents, and the borane species were separated from the free phosphines by using water / organic phase separations. The various extraction coefficients of the amine-borane complexes were determined. All the newly prepared heteronuclear ligands were used in a variety of catalytic transformations, including reactions catalysed by palladium, chromium and rhodium. The results obtained from these catalytic transformations indicated that most of these ligands afforded highly active catalysts in the different applications, and results were, in many cases, better than those obtained with commercially available ligands such as triphenylphosphine and dppp. To end off this study, an investigation towards the ó-donating properties of a selection of phosphine ligands was performed by converting the phosphines into their corresponding phosphine selenides, and calculating the 1J(77Se-31P) coupling constants. From this study, it was found that the electronic nature of different phosphine atoms in the same ligand could be characterised, and such information, in turn, can be used for the design of new ligands for specific catalytic systems. / Prof. D.B.G. Williams

The objective of the research described in this dissertation was the search for optimum ligand-metal complex combination that would facilitate the contrathermodynamic isomerisation of internal olefins. To this end a variety of ligands where synthesised and subsequently tested, firstly for their ability to isomerise alpha olefins and secondly their ability to isomerise internal olefins. Due to the lack of information obtainable from literature about catalytic isomerisation of olefins, the general reaction parameters had to be investigated. Various factors that could play a role in the isomerisation of olefins where investigated and these included the effect that solvents have on the isomerisation as well as the possibility of metalhydride formation. The possible formation of metal-hydrides was tested by adding a variety of acids and also the addition of hydrogen gas to the solution. All of these factors played an important role in the subsequent isomerisation of alkenes and valuable data could be obtained from these experiments. Solvents were found to have an effect on the isomerisation, but a trend could not be established. The effect of added acid was more pronounced and a correlation between acid strength and isomerisation could be established. It was also found that hydrogen gas added to the reaction mixture generally increased the reactivity of the metal catalysts and some experiments were done to optimise the use of hydrogen in these reactions. The use of commercially available ligands for the isomerisation reaction was also investigated and gave a broad indication of possible active ligands. After these initial reactions and information gathered from literature, it was decided to synthesise a set of di-imine ligands and also a set of bis-phisphite ligands. Due to tautomerism of the di-imines to the corresponding enamines, a set of enamine/imine ligands was synthesised and tested with two rhodium and two palladium catalysts. The synthesis of bis-phosphite ligands was initially problematic, but ideal conditions were found and a set of bis-phosphite ligands was synthesised and tested. Results obtained from the testing of both the enamine/imine lignds as well as the bisiii phosphite ligands were of value and a great many trends could be observed. Many of these observations had correlations to either the electronic nature of the various ligands as well as that of the metal centre. The testing of a set of palladium(II) metallocycles also gave an insight into the electronic properties necessary for the successful isomerisation of olefins. These electronic properties are always a combination of ligand and metal centre effects and thus a fine balance must be struck between these two factors. As a final conclusion to the work that was performed, internal olefins were subjected to tandem isomerisation-hydroformylation reactions using some of the more active metal-ligand systems. Internal olefins were isomerised and hydroformylated in the same reaction vessel to afford branched and linear aldehydes. In these reactions, it was proved that isomerisation as a primary reaction could be coupled to a secondary reaction and be of use in industry and further research in this field might prove to be of some value. / Prof. D.B.G. Williams

Several Schiff base ligands, N, N‟-(aryl)benzyaldiimine ligands (R-BEN); N, N‟-(aryl)benzyaldiamine dihydrochloride ligands (R-BENH•2HCl); N, N‟-(aryl)benzyaldiamine ligands (R-BENH); N, N‟-bis(cinnamaldiimine) ligands (R-CA2EN) were synthesized for the investigation of the electronic effect of the substituents at para-position of the Schiff base ligands and their copper complexes. The synthesis of Schiff bases was carried out by reacting a series of para-substituted benzyaldehyde, and para-substituted cinnamaldehyde with ethylenediamine. The imine group of Schiff bases, N, N‟-(aryl)benzyaldiimine ligands and N, N‟-bis(cinnamaldiimine)ligands were reduced to corresponding amines with sodium borohydride in methanol These ligands, N, N‟-(aryl)benzyaldiamine ligands (H-BENH), N, N‟-bis(cinnamaldiimine)ligands (CA2EN) were reacted with copper(II) dihalide and copper(I) monohalide ions respectively to form complexes. The ligands and their complexes were analysed using elemental analyses, FT-IR spectroscopy (mid-IR), UV/vis in aprotic and protic solvents,while mass spectrometry, 1H-NMR and 13C-NMR were used to further analyse the ligands. By using substituent parameters, both the single and dual substituent parameters with the spectroscopic data obtained from the spectroscopic techiques mentioned above, it was hoped to monitor and determine whether the electronic effects (resonance or inductive effcets) was predominantly within the Schiff base ligands and copper complexes. The NMR studies with dual substituent parameters suggest that the effects of the substituents are transimitted through the ligands, via resonance effects and that the phenyl group is nonplanar with the azomethine in N, N‟-(aryl)benzyaldiimine ligands. The presence of an extra double bond in Schiff base {(N, N‟-bis(cinnamaldiimine) ligand)} altered the electron density. The UV/vis studies showed that the symmetry of the N, N‟-bis(4-R-benzyl)-1, 2-diaminoethanedihalidecopper(II) complexes were predominantly tetrahedral for both chloro and bromo complexes. The correlation studies from mid-infrared were beneficial in monitoring the effect experienced by N, N‟-(aryl)benzaldiimine ligands, the studies suggest that the inductive effect is more pronounced at the C=N.

Magister Scientiae (Medical Bioscience) - MSc(MBS) / The synthesis and characterization of pyridinyl α-diimine Pd(II) complexes having a functionalized hydrocarbon attached to the imino nitrogen was performed. The catalytic activity of these complexes were then evaluated in the polymerization of ethylene and in the Heck coupling reaction of methyl acrylate with iodobenzene. Unconjugated β-diimine complexes of palladium were also synthesized and their activities towards ethylene polymerization and the Heck coupling of methyl acrylate and iodobenzene also evaluated and compared to that of the α-diimine complexes. Three of the α-diimine complexes synthesized showed activity towards ethylene polymerization, these being the complexes bearing the allyl, styrene and phenol functionalities. ω-Carboxylato complexes which were also synthesized showed no activity towards ethylene polymerization. The polymer produced was found to be high density linear polyethylene with an average PDI of 2.54 with Mn values ranging between 3.42 and 6.90 x 10-5 and Mw values ranging between 6.05 and 17.6 x 10-5. The complexes bearing the allyl, styrene and phenol functionalities, as well as the ω-carboxylato complexes active in the Heck coupling reactions of methyl acrylate with iodobenzene. None of the unconjugated β-diimine complexes prepared showed any activity towards ethylene polymerization even at high Al/Pd ratios. The activity of these complexes towards the Heck arylation reaction was comparable to that of the α-diimine complexes showing similar activities. / South Africa

No description available.

This thesis is concerned with the problems of sample preparation arising in the study of lead isotope abundances. The importance of this study to geophysics has been amply shown by R.D. Russell, R.M. Farquhar, F.G. Houtermans, J.T. Wilson, H.F. Ehrenberg and many others. Chapter 1 gives an outline of lead isotope measurement techniques, including types of mass spectrometers generally used and some of the problems encountered. The mass spectrometer used in the present research was designed and constructed by R.D. Russell and F. Kollar and descriptions of it will be found in their publications and in F. Kollar's Ph.D. thesis. The present techniques of producing lead tetramethyl for isotopic analysis from ore samples are discussed in Chapter 2. The remaining chapters deal with the purification of lead tetramethyl for mass spectrometer analysis, using vapour phase chromatography. This technique has found immediate application in the precise intercomparison of lead samples recently carried out in the Geophysics Laboratory at the University of British Columbia by F. Kollar and others (F. Kollar, R.D. Russell and T.J. Ulrych, in press). The long range object for developing this technique is to purify lead tetramethyl prepared by free methyl radicals reacting with metallic lead (cf. A.J. Surkan 1956) prior to isotopic analysis. The presence of impurities in samples prepared this way has discouraged the development of this method in the past. The final chapter deals with this aspect of the proposed problem. This thesis is intended as a preliminary to the writer's Ph.D. research which will also deal with isotopic lead analysis. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The redox behavior of a series of organometallic complexes containing Cp'M(NO) groups (Cp' = ƞ⁵-C₅H₅(Cp) or ƞ⁵-C₅Me₅(Cp*) ; M = Mo or W) has been investigated both by cyclic voltammetry and by chemical means. The neutral 16-electron Cp'Mo(N0)X₂ compounds (X = CL, Br or I) undergo a single, essentially reversible, one-electron reduction in CH₂CL₂/O.1M [n-Bu₄N]PF₆ at relatively low potentials (<-0.1 V vs SCE). The electrochemically observed reductions can be effected on a preparative scale by employing CP₂C0 as the chemical reductant. The isolable 17-electron [Cp'Mo (NO)X₂]•⁻ radical anions are cleanly reconverted to their 16-electron neutral precursors by treatment with [Cp₂Fe]BF₄. In contrast, the Cp'W(NO)I₂ compounds undergo rapid decomposition to their [Cp'W(NO)I]₂ monohalo dimers upon electrochemical reduction. Electrophiles NE⁺ (E = O or ϱ-O₂NC₆H₄N) undergo unprecedented insertions into the Cr-C ϭ-bonds of CpCr(NO)₂R complexes (R = Me, CH₂SiMe₃ or Ph) to afford [CpCr(N0)₂{N(E)R}]⁺ cationic complexes. Present evidence is consistent with these insertions occurring via charge-controlled, intermolecular attacks by NE⁺ at the Cr-R groups in classical SE2 processes. The newly-formed N(E)R ligands function as Lewis bases through nitrogen atoms toward the formally 16-electron [CpCr(NO)₂]⁺ cations and may be displaced from the chromium's coordination sphere by the more strongly coordinating CL⁻ anion. The resulting CpCr(NO)₂CL can be reconverted to CpCr(NO)₂R. thereby completing a cycle by regenerating the initial organometallic reactant. The entire sequence of stoichiometric reactions forming the cycle thus constitutes a selective method for the formation of new carbon-nitrogen bonds, the net organic conversions mediated by the CpCr(NO)₂ group being NE⁺ + R⁻ → N(E)R. The electrophilic [Cp'M(NO)₂]⁺ cations (Cp'=Cp or Cp* ; M = Cr, Mo or W) condense with methyl propiolate and 2,3-dimethyl-2-butene to afford cationic organometallic lactone complexes. These complexes undergo facile ⍜-dealkylation to yield the neutral Cp'M(NO)₂(ƞ¹-lactone) derivatives. Furthermore, the neutral Cp'W(NO)₂(ƞ¹-lactone) compounds decompose in air to their Cp'W(O)₂(ƞ¹-lactone) dioxo products. / Science, Faculty of / Chemistry, Department of / Graduate

Although hydrides of metal carbonyls are widely known, the number of hydrides in the related family of metal nitrosyls is extremely small. The preparation of a series of nitrosyl hydrides from the treatment of [CpW(NO)I₂]₂ (Cp=ƞ⁵-C₅H₅) with Na[H₂Al(OCH₂CH₂OCH₃)₂] is described. The addition of one or two equivalents of the aluminum reagent results in the formation of [CpW(NO)IH]₂ or [CpW(NO)H₂]₂ respectively. The reaction of [CpW(NO)IH]₂ with a Lewis base (L=P(OPh)₃, P(OMe)₃, PPh₃ or PMe₃) gives the monometallic CpW(NO)IHL, while [CpW(NO)H₂]₂ reacts with P(OPh)₃ or P(OMe)₃ to yield [CpW(NO)HL]₂ which undergoes further reaction to give CpW(NO)H₂L. Proton NMR spectroscopy shows that all bimetallic species contain bridging hydride ligands and are therefore best, formulated as [CpW(NO)1]₂(µ-H)₂, [CpW(NO)H]₂(µ-H)₂ and [CpW(NO)L]₂(µ-H)₂. The ¹H NMR spectrum of [CpW(NO)H]₂(µ-H)₂ shows that there is no hydride ligand exchange on the NMR time scale and that ¹jH(terminal)W ≃ ¹jH(bridging)w > ²jHW. From this finding, it is possible to develop new criteria for assessing the static or fluxional nature of hydride ligands for several families of organotungsten hydrides (Cp₂W, CpW(CO)₃, W(CO)₃ and CpW(NO)x (x=l or 2)). Within each family, the magnitude of ¹JHW strongly reflects the type of metal hydride bonding, i.e. [Formula Omitted] and suggests that bridge bonding involves all the atoms in the bridge and therefore the "fused" notation is introduced. Treatment of CpW(NO)(CH₂SiMe₃)₂ with low pressures of H₂ (60-80 psig) in the presence of Lewis bases (L=P(0Ph)₃, PMePh₂) gives the unusually stable alkyl hydride compounds CpW(NO)(H)(CH₂SiMe₃)L. This chemistry is then extended to the Cp* (Cp*=ƞ⁵ -C₅Me₅) analogues, including the preparation of the appropriate starting materials. Upon thermolysis of Cp*W(NO)(H)(CH₂SiMe₃)(PMe₃) in C₆H₆, the intermolecular C-H activation product Cp*W(N0)(H)(C₆H₅)(PMe₃) is cleanly formed. However, intermolecular activation of CH₄, C₆H₁₂ or n-C₆H₁₄ does not occur under similar experimental conditions. Hydrogenolysis of Cp*W(NO)(CH₂SiMe₃)₂ at high pressures (≃920 psig) with no Lewis base present results in the formation of isolable [Cp*W(NO)H]₂(µ-H)₂ and [Cp*W(N0)H](µ-H)₂[Cp*W(N0)(CH₂SiMe₃)]. The latter is a new example of the rare class of dinuclear alkyl hydride complexes. Proton NMR spin tickling experiments on this compound allow the complete assignment of all couplings in the spectrum and show that ¹jH(terminal)W' ¹JH(bridging)W and ²jHW have the same sign. / Science, Faculty of / Chemistry, Department of / Graduate

The nitrosyl complex CpW(NO)R₂ (R = CH₂SiMe₃) forms 1:1 adducts via isonitrosyl linkages to Lewis acids such as AlMe₃ and Cp₃Er, i.e. CpWR₂(NO→A) (A = AlMe₃, ErCp₃). These adducts regenerate the starting dialkyl complex when treated with water. Protonation of CpW(NO)R₂ by HBF₄⋅0Me₂ can also be effected. Whether the site of protonation is the nitrogen or the oxygen atom of the nitrosyl ligand is not known with certainty, although O-protonation is postulated by analogy with the other Lewis-acid adducts of CpW(NO)R₂. In these adducts, the nitrosyl stretching frequency is shifted to lower wavenumbers relative to that of the parent dialkyl, to an extent which increases as harder Lewis acids are employed. The colour of the adducts also ranges from red to orange to yellow as progressively harder acids are used. Treatment of CpW(NO) (CH₂SiMe₃)₂ with [Ph₃C]⁺ PF₆⁻ in Ch₂CL₂ results in electrophilic cleavage of a carbon-silicon bond to yield the mixed dialkyl CpW(NO)(CH₂SiMe₃)(CH₂CPh₃), which has been fully characterized by spectroscopic methods and by a single-crystal X-ray crystallographic study. The formation of Me₃SiF and PF₅ (coordinated to Lewis bases in the reaction mixture) as by-products of this reaction has been confirmed by ³¹P and ¹⁹F NMR spectroscopy of the reaction mixture in CD₂CL₂. Preliminary attempts to extend this novel reaction of a silicon-containing ligand by using other carbocations were unsuccessful. This is attributed to the high reactivity of the required carbocations and the large number of possible reaction sites on the metal complex. Some reactions of the mixed dialkyl CpW(NO)RR¹ (R = CH₂SiMe₃ R¹ = CH₂CPh₃) were found to be analogous to those of the parent CpW(NO)R₂, while other reactions followed a different course because of the ability of the CH₂CPh₃ ligand to orthometallate. Thus, CpW(NO)RR¹ is much less thermally stable than CpW(NO)R₂. As a solid or a solution in non-coordinating solvents, it decomposes in a matter of days at room temperatures to a mixture of products which were not identified. In acetonitrile solution, an orthometallated complex derived from CpW(NO)RR¹ can be trapped by coordination of solvent. The product CpW(NO)(CH₂C(C₆H₄)Ph₂)(NCMe) has been isolated and crystallographically characterized. Cyclic voltammograms of CpW(NO)R₂ and CpW(NO)RR¹ show that both complexes undergo an apparently chemically reversible reduction and an irreversible oxidation. The mixed dialkyl CpW(NO)RR¹ is somewhat easier both to reduce and to oxidize than CpW(NO)R₂. Like CpW(NO)R₂, CpW(NO)RR¹ reversibly forms a 1:1 adduct with PMe₃. Also analogously to CpW(NO)R₂, it reacts with 0₂ to form a 5:1 mixture of dioxoalkyl complexes CpW(0)₂R and CpW(0)₂R¹, and with NO(g) to form 2 CpW(NO)R¹(ƞ² -0₂N₂R). In this product, insertion of NO has occurred exclusively in the W-CH₂SiMe₃ bond. Upon photolysis, both complexes CpW(NO)R¹¹(ƞ²-0₂N₂R) (R¹¹ = CH₂SiMe₃ or CH₂CPh₃) form dioxo alkyls CpW(O)₂R¹¹ in an unprecedented reaction. The ability of CpW(NO)RR¹ to orthometallate also results in the formation, when this complex is treated with sulphur, of CpW(O)(CH₂C(C₆H₄)Ph₂)-(SR). No analogue to this compound can be obtained from reaction of CpW(NO)R₂ with sulphur. The sequence of reactions leading to the formation of this product is not known. / Science, Faculty of / Chemistry, Department of / Graduate

The main objective of the research described in this dissertation was the preparation of a range of bulky and electron-rich phosphine ligands using the DoM methodology developed in our labs for this purpose. These ligands would be employed in the Suzuki cross-coupling reaction of deactivated aryl bromides and aryl chlorides. Initially, a range of phosphinic amides was synthesised and tested for DoM reactivity. TMSCl, MeI and O2 were successfully used as electrophiles, incorporating TMS, Me and OH groups in the ortho-position of these phosphinic amide systems. This development was encouraging and provided a route to incorporate a phosphine on the ortho-position of these phosphinic amide systems by using Ph2PCl and Cy2PCl as electrophiles to incorporate Ph2P and Cy2P, respectively. The route was versatile and a range of electrophiles was used to prepare phosphine ligands with varying electronic and steric properties. These electrophiles (of the R2PCl variety) were often specifically prepared from PCl3 and the corresponding Grignard reagent. Phosphine ligands synthesised in this research project using our DoM (directed ortho metallation) methodology were tested in Suzuki cross-coupling reactions of deactivated aryl bromides and some aryl chlorides and showed excellent reactivity, with the advantage that the ligands of this study are oxidatively and hydrolytically stable. Efforts were also made to modifying the phosphinic amide-functionalised phosphine ligands to generate their water-soluble derivatives. One way of achieving this was by the hydrolysis of the phosphinic amide moiety to the phosphinic acid analogue. Salts of these phosphinic acid derivatives have promising activities as water-soluble substrates. This route was successful only iii with less electron-rich systems providing an opening for more research in this regard. In an alternative synthetic route to polar water-soluble phosphines it was envisioned that phosphonate-derivatised phosphines would offer access to water-soluble phosphine ligands by using milder hydrolysis conditions. These phosphonate systems were also tested for DoM reactivity and showed promising reactivity. Phosphonates have not previously being employed as DoM groups, and this alone expands the application and potential scope of P-based DoM groups. / Prof. D.B.G. Williams