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Hybrid inorganic-organic networks have been studied in both chemistry and materials science due to properties, (e.g. porosity, magnetic and electronic behaviors) that may lead to applications in catalysis, gas absorption and storage. It is important to understand the different structural topologies shown by hybrid networks to help develop practical applications for these materials. The research is focused on the design and synthesis of well-defined hybrid network structures that have potential to contain molecular size cavities that can be used for catalysis and gas storage. In the field of organic-inorganic hybrid networks, the goals are to design and synthesize 1D, 2D and 3D networks with cavities, and to characterize them by X-ray, TGA and surface area measurements. Twenty-six networks have been successfully made with interesting structure topologies. These hybrid network structures are classified into three series based on their ligands. Series I contains ten hybrid networks constructed from the flexible ligand, 4, 4′-trimethylenedipyridine (TMDP), Zn2+ ions, and H3PO3, and with aromatic alcohols as templates to direct the formation of various hybrid network structures. Series II consists of five structures constructed from the relatively rigid ligand, 4, ′-bisimidazolelybipyridine (BIB) with metal ions (Cu2+, Ni2+) and the conjugated bases of H3PO3 and H3PO4. The BIB ligand is not commercially available so is produced and characterized by NMR, mass spectrometry and TGA. Rigid network structures were expected to construct with pores of molecular dimensions with the BIB ligand. To date, the BIB ligand has not yield the desired porous network, however, these 3D hybrid networks have interesting topologies, one of which is an interdigitated network that is the precursor for 3D interpenetrated networks. Series III contains five hybrid structures constructed from various organic ligands, such as tartaric acid, picolinic acid and 1, 2, 4-triazole. In addition to the hybrid networks, six hydrogen bonded networks were prepared. Graph-Analysis is applied to study these hydrogen bonded network structures. The Ï â ¦.Ï interaction is also discussed within the hydrogen bonded networks. / Ph. D.

Manganese(II) and (III) complexes of potentially bidentate and tridentate Schiff base ligands have been prepared. The ligands were prepared from substituted salicylaldehyde or pyridine-2-carboxaldehyde and amines with hydrocarbon or alkylpyridyl substituents. The electrochemistry and the oxygenation kinetics of these and similar tetradentate, pentadentate, and hexadentate complexes have been studied. The electrochemistry of the majority of the complexes involves the Mn(III)/Mn(II) couple. However, varying the solvent shows that electron transfer is often accompanied by slow changes in the number of solvent molecules coordinated to the metal or changes in the actual denticity of the ligand. Activation energies and entropies for the reactions with 0₂ show that a large number of parameters influence the rate of reaction. Primary among these is competition between 0₂, solvent molecules, and donor atoms from the ligands for coordination sites on the metal. However, the reactions were all (with one exception) found to be first order in both complex and 0₂, implying that the slow step is formation of a Mn(III)-superoxo complex. The exception was with complexes of the tetradentate Mn(SALC_n) type, where a simple rate law could not be fitted. This was explained by either steric hindrance or polymerization of the complex due to the flexibility imparted by the long polymethylene chain in the tetradentate ligand. / Ph. D.

The complex, IrH₂(PMe₃)₃Cl (1), was previously found to be, not only unexpectedly water-soluble but also an effective homogeneous catatyst for the hydrogenation of unsaturates in water. The results of extensive ³¹P NMR studies on the aqueous system of (1) indicate that (1) is in equilibrium with the iridium(III) dihydrido “aquo” complex, [IrH₂(PMe₃)₃(H₂O)]⁺, and not the μ-chloro bridged complex, { [IrH₂(PMe₃)₃]₂Cl}⁺ (2), as previously reported. The calculated K_eq value for the aqueous equilibrium is (0.0037 ± 0.0003) M. Thermodynamic data (ΔH = 30.8 kJ/mol, ΔS = 56.0 J/(Kmol), and ΔG = 14.1 kJ/mol) obtained from variable temperature ³¹P NMR studies are consistent with the proposed equilibrium system. The complexes IrH₂(PMe₃)₃X (X = O₂CPh (3), I (4), and Br (6) were synthesized and examined. The complexes IrH₂(PMe₃)₃X (X = H₂O and F) could not be isolated. (3) was determined to dissociate completely in water to form the iridium(III) dihydrido “‘aquo” complex, [IrH₂(PMe₃)₃(H₂O)]⁺, seemingly explaining the greater catalytic activity of (3). Solubility of the halo complexes decreased from moderately soluble (1), to slightly soluble (6), to very slightly soluble (4). The solubilities of (4) and (6) were too low to allow quantification of their equilibria. Finally it was observed that linear relationships exist between the electronegativity of the ligand, X, and the ¹H and ³¹P NMR chemical shifts of the hydrides and the phosphines for the complexes, IrH₂(PMe₃)₃X. These relationships are consistent with the findings of Birnbaum. / Ph. D.

The versatility of organoboron compounds has been demonstrated by their use as synthetic intermediates and more recently in therapeutic applications since the FDA approval of Velcade©. As a result, transition metal-catalyzed protocols to incorporate boron reagents into unsaturated compounds have been extensively researched. While an abundance of literature protocols have been reported, the majority utilize harsh reaction conditions in combination with expensive reagents. This dissertation discloses the author’s contributions to the development of efficient, cost-effective, and operationally simple transition metal-catalyzed borylation protocols with alkynes and diboron reagents. An open-to-air copper(II)-catalyzed aqueous borylation protocol of alkynoates and a symmetrical diboron reagent is reported. Conjugate addition of the boryl-copper species to the electrophilic β-carbon provided β-boryl-α,β-unsaturated esters in moderate to excellent yields. Exclusive (Z)-stereochemistry was confirmed by nOe experiments. The resulting vinyl boronate esters are useful cross-coupling partners. The scope of the aqueous β-borylation protocol was extended to the unsymmetrical diboron reagent, pinB-Bdan. This alternative protecting group has emerged as an orthogonal protecting group and alters the reactivity of the boron moiety. Activation of the pinacol moiety to form the Lewis acid-base adduct allowed for the chemoselective transfer of the 1,8- diaminonapthalene moiety to the β-carbon. An alternative novel synthesis of vinyl, allyl diboronate esters from propargylic alcohols has also been described. Formation of a leaving group in-situ with a palladium- and coppercatalyzed protocol can lead to several competing reaction pathways and the formation of multiple products. Fortunately, the resulting vinyl, allyl diboronate esters were stereoselectively synthesized in moderate GC yields despite significate decomposition during purification, as confirmed by stability studies. The terminal diboration of allenes was previously the only reported method for the synthesis of vinyl, allyl diboronate esters. / Ph. D. / The unique properties of organoboron compounds allow them to be used as synthetic intermediates and as drugs targets. This dissertation discloses three environmentally friendly and simple methods to incorporate boron into alkynes using transition metal catalysts. In particular, alkynoates were successfully borylated under copper(II)-catalyzed aqueous conditions using symmetrical and unsymmetrical diboron reagents. Propargylic alcohols were also borylated using bimetallic conditions to afford vinyl, allyl diboronate esters, which were previously hard to obtain.

Thesis (MSc (Chemistry and Polymer Science))--Stellenbosch University, 2008. / The competitive transport, extraction, and coordination chemistry for a series of N- (thio)phosphorylated (thio)amide and N-(thio)phosphorylated (thio)urea ligands were investigated with the seven transition and post-transition metal ions Co(II), Ni(II), Cu(II), Zn(II), Ag(I), Cd(II) and Pb(II). Three N-benzylated derivatives of 1,4,7,10- tetraazacyclododecane (cyclen) were synthesized and a similar study carried out with the same metal ions and the deprotonated precursors. The ligands were all potential specific carriers (ionophores) in the organic phase. The seven metal ions had equal concentrations in the source phase. The experimental arrangement for the transport studies employed a set-up involving three phases: a source phase and a receiving phase (both aqueous), separated by a chloroform membrane (organic phase). Competitive metal ion solvent extraction involved two phases: an aqueous phase and an organic phase. Similar conditions were used in transport and extraction studies. The metal ion concentrations in the aqueous phases were analyzed by atomic absorption spectroscopy (AAS). The transport results of deprotonated N-(thio)phosphorylated (thio)amides and N- (thio)phosphoryated (thio)ureas showed that PhC(S)NPO(OPri)2 (L1), BrPhC(S)NPO-(OPri)2 (L11) and PriNHC(S)NPO(OPri)2 (L16) transported Ag(I) into the receiving phase. Under these experimental conditions, L1 had the highest Ag(I) transport efficiency, at 36.3%, while L11 only transported one metal ion, viz. Ag(I). With NH2C(S)NP(S)(OPri)2 (L4), 94.6% of Ag(I) remained in the membrane phase. Thus L4 appeared to have the highest formation constant with Ag(I). A small amount of Cu(II) was also transported by L1, NH2C(S)NP(O)(OPri)2 (L9), L16 and ButNHC(S)-NPO(OPri)2 (L20). L20 had the highest selectivity for Cu(II). Results of competitive metal ion extraction studies revealed that most ligands extracted up to 100% Ag(I), except L1 and morpholine substituted ligands (L7, L17) . The formation constant of L1 effects a subtle balance between metal uptake and metal loss into and out of the respective membrane phase. HL7 and HL17 had low solubility in chloroform. L4 extracted the highest percentage of Cu(II) (49%). Two neutral ligands, PhCONHPO(OPri)2 (1) and BrPhCONHPO(OPri)2 (2) were isolated and their molecular structure determined. They had monoclinic unit cells in the space groups C2/c and P21/n, respectively. An unprecedented octanuclear [Ag(I)(L4-S,N)]8 (3) complex was also crystallized. The extended structure showed three different cavities alternating with two unique 16-membered rings, creating a novel AgS2N2 cage. Two polynuclear Cu(I) chelates with deprotonated L4 and L6 (tBuNHC(S)NP(S)(OPri)2) were isolated by the same crystallization method. The complex [Cu(I)(L4–S,S)]9 (4) consisted of a hexagonal-prismatic hexamer, which exhibited an unusual and unprecedented supramolecular “honeycomb” packing. The trinuclear [Cu(I)(L6–S,S)]3 (5) consisted of a 6-membered Cu3S3 ring attached to a hydroxy tetrahydrofuran molecule. Di-, tri- and tetra-benzyl-1,4,7,10-tetraazacyclododecane (cyclen) was synthesized, and characterized. None of these compounds was effective in metal transport under these experimental conditions. Nevertheless, Tetra-benzyl cyclen showed the highest extraction efficiency for Ag(I), at 100%, and the highest selectivity for Ag(I) extraction, compared to Cu(II). An intermediate of dibenzyl cyclen compound dibenzylated dioxocyclen (6) was crystallized and found a host THF molecule in the lattice. The crystal and molecular structure confirmed the cis-configuration. The X-ray structure of the Cu(II) complex with dibenzylated cyclen (7) was determined for the first time. It was found to have an ideal square pyramidal coordination geometry around the central metal ion. A serendipitous organic compound of isopropylammonium(isopropylamino)- oxoacetate mono-hydrate (8) was crystallized. The crystal was held together by inter-molecular hydrogen bonds, which lead to two-dimensional layers with hydrophobic interactions.

<p>In view of the important applications of carbides and carbo-nitrides of transition metals in the heat-resistant and hard materials industries, the thermodynamic activities of Cr and Mn in the Cr-C, Fe-Cr-C, Mn-Ni-C and Mn-Ni-C-N systems have been studied in the present work by the use of the galvanic cell technique. CaF₂single crystals were used as the solid electrolyte. The phase relationships in selected regions of the systems in question were investigated by the use of the equilibration technique. The phase compositions and microstructures of the alloys were analysed by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM).</p><p>In the Cr-C system, the Gibbs energy of formation of Cr3C2 were obtained from ElectroMotive Force (EMF) measurements conducted in the temperature range 950-1150 K. The values of the enthalpy of formation of Cr₃C₂ were evaluated by the third-law method. The ground-state energy of the hypothetic end-member compound CrC3, in the bcc structure at 0 K, was calculated by use of the Ab-initio method. Based on the obtained results the Cr-C system was reassessed by use of the CALPHAD approach.</p><p>In the Fe-Cr-C system, 16 different alloys were quenched at 1223 K and their equilibrium phases identified by XRD. The experimental results show that the substitution of Cr by Fe in the (Cr,Fe)₇C₃ carbide changes the lattice parameters of the phase. A slight decrease of the lattice parameters with an increase in the Fe content was established. The lattice parameters of the γ-phase in the Fe-Cr solid solution did also show a decrease with an increase of the Fe content. The activities of chromium in Fe-Cr-C alloys were investigated in the temperature range 940-1155 K. The activity of chromium decreases with an increase in the Fe content when the ratio of C/(Cr+C) was constant. It was also established that the activity of chromium decreases with an increase of the carbon content when the iron content was constant. The experimental results obtained were compared with the data calculated by use of the Thermo-Calc software. </p><p>In the Mn-Ni-C system the phase relationships were investigated at 1073 K as well as at 1223 K. The experimental results obtained showed that the site fraction of Ni in the metallic sublattice of the carbides M₂₃C₆, M₇C₃ and M₅C₂ (M=Mn and Ni) was quite low (approximately 2~3 percent). The activities of manganese in Mn-Ni-C alloys were investigated in the temperature range 940-1165 K. The three-phase region γ/M₇C₃/graphite was partly constructed at 1073 K. </p><p>In the Mn-Ni-C-N system, nitrogen was introduced into Mn-Ni-C alloys by equilibrating with N2 gas. It was established that the solubility of nitrogen in the investigated alloys was effected by the carbon content, and that a (Mn,Ni)₄(N,C) compound was formed in the nitrided alloys. EMF measurements were performed on Mn-Ni-C-N alloys in the temperature interval 940-1127 K. The addition of nitrogen to Mn-Ni-C alloys was found to decrease the activity of manganese. The negative effect of nitrogen on the activity of manganese was found to decrease as the carbon content increased.</p><p><b>Keywords:</b> Thermodynamic activity; Galvanic cell technique; Transition metal carbides; Transition metal nitrides; Phase equilibrium; Thermodynamics; Differential thermal analysis; Scanning electron microscopy; Transmission electron microscopy; Ab-initio calculations; CALPHAD approach;</p>