Thesis (Ph. D.) University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on July 30, 2006). Includes bibliographical references.

This is the first report that demonstrates the ability of anaerobic methanogenic granular sludge to reduce Rh(III) to Rh(0). Recovery of rhodium(Rh) during anaerobic incubations under abiotic and biotic condition with different electron donors was studied. H2 and formate reduced Rh(III) to Rh(0) nanoparticles(NPs) in the absence of microorganisms. However, the presence of microorganism was crucial for Rh(III) reduction with ethanol. Results of X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) confirmed the formation of Rh(0) NPs and indicated the localization and morphology of the formed Rh(0) NPs varied with electron donor utilized. Rh(III) reduction with H2 and ethanol obeyed 1st order kinetics. Rh(III) caused a moderate inhibition to methanogenesis. Rh(III) reduction often ceased before coming to completion but this effect is not due to unfavorable thermodynamics. A hypothesis was developed which ascribes the biological reduction of Rh(III) with ethanol as being due to the biological formation of H2 (that subsequently chemically reacts with Rh). The results obtained indicate the potential of utilizing anaerobic granular sludge bioreactor technology as a practical and promising option in Rh(III) recovery.

Poly(vinylbenzylchloride) (PVBC) nanofibers were fabricated by the electrospinning process. The Merrifield micropheres, silica microsparticles and PVBC nanofibers were functionalised with different quaternary diammonium groups derived from ethylenediamine (EDA), tetramethylenediamine (TMDA), hexamethylenediamine (HMDA), 1,8-diaminooctane (OMDA), 1,10-diaminodecane (DMDA) and 1,12-diaminododecane (DDMDA) and investigated for separation of [RhCl5(H2O)]2- and [IrCl6]2-. The sorbent materials were characterised by means of FTIR, XPS, SEM, BET surface area, thermogravimetric analysis and elemental analysis, and characterization results showed that the functionalization of the sorbent materials was successful. Batch equilibrium studies were carried out to assess the efficiency of these different anion exchangers using single metal aqueous solutions. The adsorption isotherms and kinetics of both [RhCl5(H2O)]2- and [IrCl6]2- adsorption onto the sorbent materials are presented. The isothermal batch adsorption studies fitted the Freundlich model indicating heterogeneous surface adsorption. The Freundlich isotherm confirmed multilayer adsorption and the Freundlich constant (kf) displayed the following ascending order for nanofibers (F-QUAT EDA, F-QUAT TMDA, F-QUAT HMDA, F-QUAT OMDA and F-QUAT DMDA), silica microparticles (Si-QUAT EDA, Si-QUAT TMDA, Si-QUAT HMDA, Si-QUAT OMDA and Si-QUAT DMDA) and microspheres (B-QUAT EDA, B-QUAT TMDA, B-QUAT HMDA, B-QUAT OMDA and B-QUAT DMDA) and a decrease in kf for F-QUAT DDMDA, Si-QUAT DDMDA and B-QUAT DDMDA has been observed. The pseudo second-order model was found to be the best fit to describe the adsorption kinetics of both metal ions complexes onto all the sorbent materials. K2 value in pseudo second-order kinetics showed that the rate constant for adsorption of [IrCl6]2- onto nanofibers was larger than for silica microparticles and Merrifield microspheres. Column sorption of [IrCl6]2- and [RhCl5(H2O)]2- was carried out and the loading capacities of [IrCl6]2- were obtained, and they showed dependence on the length of the methylene spacer between the two diammonium centres. [RhCl5(H2O)]2- was not adsorbed by the sorbent materials while [IrCl6]2- was loaded onto the column. The highest iridium loading capacities for all the sorbent materials for the diamines with decylene spacer, and were found to be 32.94 mg/g, 29.35 mg/g, and 27.09 mg/g for F-QUAT DMDA, Si-QUAT DMDA and B-QUAT DMDA respectively. It was also observed on the derivatives of DMDA supported on nanofibers that F-QUAT ethyl loading capacity for iridium (19.89 mg/g) reduced which may be due to the electron-donating nature of the ethyl group and the increase of hydrophobicity whereas F-QUAT benzyl loading capacity (244.64 mg/g) increased dramatically due to increase in the size of the cation which lowers the positive charge density of the quaternary diammonium center. The charge delocalizing ability of the benzyl group resulted in the best interaction of the diammonium group derived from this quaternizing agent, yielding the highest loading capacity for [IrCl6]2-. Reusability was conducted and the results showed that the all the sorbent materials can be used repeatedly without decreasing their adsorption capacity significantly. The neat diammonium salts were also synthesized and interacted with the chorido metal complex anions to form ion-pairs which were then studied for their solubility. The synthesis of the quaternary salts was rather challenging and resulted in some interesting species when impurities of the iodide form of the salts were present in the process of converting them to the iodide form. Some of these include I52+, which was confirmed preliminarily by X-ray structural analysis, potentiometry and cyclic voltammetry. Molecular modeling studies were also conducted to explain the interaction of the chlorido anions with the cationic diammonium centres, and to quantify these interactions by thermodynamic parameters, partial charge calculations, dipole moments and electrostatic potentials, and there was good agreement between theory and experiment. This thesis presents iridium-specific materials that could be applied in solutions of secondary PMGs sources containing rhodium and iridium as well as in feed solutions from ore processing.

Kinetic studies of a number of interesting and significant reactions involving activation of hydrogen, olefins, oxygen and carbon monoxide by solutions of rhodium complexes containing sulphur and/or chloride ligands are described. The cis 1,2,3-trichlorotris(diethylsulphide)rhodium (III) complex, RhCl(EtS₃and the corresponding dibenzyl sulphide complex, RhCl₃(Bz₂S)₃in N,N -dimethylacetamide (DMA) solution were found to be effective catalysts for the homogeneous hydrogenation of maleic, fumaric and trans-cinnamic acids. The kinetic data are consistent with a dissociation of a sulphur ligand prior to the hydrogen reduction of rhodium (III) to rhodium (I). The rhodium (I) is stablized in solution by rapid complexing with the olefin to produce a Rh¹(olefin)(Ln) complex (L = auxiliary ligands) which then reacts with H₂ in a rate determining step to produce the saturated paraffin and rhodium (I). In some instances, more complex kinetics resulted when one of the auxiliary ligands in the Rh¹ (olefin)(Ln) complex dissociates prior to reaction with H(2); a unique apparent zero order in catalyst concentration has been observed. Isomerization was observed in the RhCl(EtS)₃catalyzed hydrogenation of fumaric acid and a mechanism involving rhodium (III) alkyl intermediate seems likely. The cyclooctene complex, [Rh(C8H14)₂C1], in DMA was found to be a convenient source for preparing rhodium (I) complexes "in situ" by adding the desired ligands, for example, chloride or diethyl sulphide. Kinetic data obtained using such solutions are in good agreement with the hydrogenation data obtained by starting from the corresponding rhodium (III) complexes. This result confirms that rhodium (I) intermediates are involved in the catalytic hydrogenation starting from rhodium (III) complexes. During studies to investigate the effect of solvent on catalytic hydrogenation of olefins by rhodium (III) complexes, dimethyl sulphoxide (DMSO) was found to be catalytically reduced by hydrogen to dimethyl sulphide and water in the presence of RhCl(EtS)₃ and RhCl‧3H2O. The kinetics were consistent with a rate determining heterolytic splitting of H₂ by Rh(III)(DMSO) to produce Rh[III](DMSO)H¯ which then decomposes to the products in a fast step. RhCl₃‧3H₂O also catalyzed the oxidation of DMSO to dimethyl sulphone using a mixture of oxygen and hydrogen. The solution of [Rh(C8H14)₂C1]₂ in DMA containing LiCl was found to be a versatile catalyst, for besides the activation of hydrogen and olefins, oxygen and carbon monoxide could also be activated. The formation of a rhodium (I) molecular oxygen complex, Rh(I)(O2) and a subsequent catalyzed oxidation of the DMA solvent and cyclooctene were studied in detail. The formation of the Rh(I)(O2) complex appears to be irreversible. An E.S.R. signal, possibly due to species such as Rh(II)(O2¯) was also observed. The kinetics of the oxidation suggest the equilibrium formation of the Rh(I)(O2) complex followed by a rate determining step to give the products. A free radical mechanism seems likely. Solutions of [Rh(C8H14)₂C1]₂ in LiCl/DMA readily reacted with carbon monoxide to form a Rh(I)(CO)₂ species. A solution of the oxygen complex was converted more slowly to the Rh(I)(CO)₂ species in a reaction whose observed rate was determined by the dissociation of the coordinated oxygen. Preliminary studies indicated that a mixture of CO and O₂ is converted catalytically to CO₂ by a solution of [Rh(C8H14)₂C1]₂ in LiCl/DMA. / Science, Faculty of / Chemistry, Department of / Graduate

A kinetic study was undertaken to investigate the potentiality of rhodium chioro complexes containing diethyl sulphide ligands as homogeneous catalysts. Preliminary studies have also been carried out on the analogous iridium complexes and some rhodium complexes containing arsenic ligands. Under mild conditions of temperature and pressure (70-85°C and upto one atmosphere of hydrogen), it was found that cis RhCl₃(Et₂S)₃ in dimethylacetamide solution is an active catalyst for the homogeneous hydrogenation of maleic acid, trans cinnamic acid and ethylene. In benzene solution, no homogeneous hydrogenation occurred. The kinetics of the maleic acid hydrogenation have been studied in detail and it was found that the hydrogenation process consisted of two rate determining steps: the initial hydrogen reduction of Rh(III) to Rh(I) which complexed rapidly with the maleic acid present and the subsequent hydrogenation of the Rh(I) - maleic acid complex to yield succinic acid and Rh(I) again. The detailed mechanisms of these steps, with particular emphasis on solvent effects are discussed. The corresponding IrCl₃(Et₂S)₃ complex and Rh(III) complexes with "difars" and "diars" (two chelating arsenic ligands) were inactive as homogeneous hydrogenation catalysts, however reactions with H₂ were observed with the iridium complex itself and also the rhodium difars complex; these reactions are also discussed. / Science, Faculty of / Chemistry, Department of / Graduate

Current knowledge of mechanistic organometallic chemistry has resulted largely from the study of mononuclear transition metal complexes. The possibility that different primary organometallic processes involving two or more metal centres may exist has been addressed only recendy. Reactivity studies on a simple, well defined binuclear system ought to provide fundamental insights into the nature of such polynuclear primary processes. The binuclear rhodium hydrides {[R₂P(CH₂)nPR₂]Rh(μ-H)}₂ (R = Pri, n = 2-4, 1a-1c; R = OPri, n = 2, 1d) were thus reacted with a variety of organic compounds in an attempt to define primary processes involving two metal centres. The reactions of 1a-c with dihydrogen proceed rapidly to produce fluxional binuclear tetrahydrides whose structure is dependent on the chelate ring size of the diphosphine ligand. The dihydrides also catalyze the hydrogenation of olefins. Two mechanistic pathways for this cycle are proposed to exist as supported by chemical and kinetic evidence. One utilizes binuclear intermediates, the other mononuclear; the latter predominates in the 1b catalyzed system (chelate ring size of six) while the former is favoured in the cycle mediated by la (chelate ring size of five). The reactions of 1a and 1b with 1,3-dienes led to the solid (X-ray diffraction) and solution state characterization of binuclear complexes incorporating bridging dienyl ligands in the previously unobserved μ-ƞ⁴-ϭ and μ-ƞ³-ƞ³ "partial sandwich" bonding modes. A fluxional process interconverting the two bonding modes was observed spectroscopically in the products of the 1a/butadiene reaction and a model accounting for this is proposed. Labelling and alternate synthetic studies, as well as the observation of an intermediate at low temperature, support a mechanism for these reactions which involves the dehydrogenation of the dihydrides followed by further reaction of [(P₂)Rh]₂ with a second equivalent of diene. Bridging amido hydrides of general formula [(P₂)Rh]₂(μ-NR'CH₂R")(μ-H) are produced in the reactions of 1a and 1d with imines (R'N=CHR"). Mechanistic studies reveal that initial ϭ-donation of the imine lone pair; of electrons to one Rh followed by π-coordination of the C=N bond to the other precedes formal insertion of the C=N bond into Rh-H. This proposal is consistent with the results of labelling and kinetic studies, but the crux of its support lies in the spectroscopic observation of two intermediates en route to the product amido hydrides. The specific synthesis of cationic μ-ƞ²-ϭ imine complexes closely related to one of the proposed intermediates in the reaction was carried out to confirm the plausibility of such an intermediate. Reaction of the amido hydrides with dihydrogen was slow in producing free amine and the hydrogen adducts of 1a or 1d, precluding the use of these dihydrides as catalyst precursors in the homogeneous hydrogenation of imines. Reaction of 1a and 1d with nitriles (R"'C=N) produces μ-alkylideneimido hydride complexes of general formula [(P₂)Rh]₂(μ-N=CHR'")(μ-H). One derivative (P₂, R = Pri, n = 2; R"' = CH₃) has been characterized by X-ray crystallography. Further reaction of these complexes with dihydrogen yield the amido hydrides [(P₂)Rh]₂(μ-NHCH₂R"')(μ-H). No intermediates in these reactions were observed, precluding meaningful mechanistic proposals for this stepwise reduction of nitriles as mediated by two metal centres. / Science, Faculty of / Chemistry, Department of / Graduate

Rhodium(I)-bis(ditertiaryphosphine) complexes of the general formula Rh(P⁀P)₂Cl[P⁀P = Ph₂P(Ch₂)n PPh₂, n = 1-4, and (+)-diop (diop = 2,3-0 isopropylidene 2,3-dihydroxy-1,4 bis(diphenylphosphino)butane] have been prepared by treating [Rh(Ccyclooctene)C₂Cℓ]₂ with the appropriate ditertiaryphosphine. The n=1, and n=4 and diop species are five-coordinate in the solid state and in non-polar solvents, while the n=2 and 3 species contain ionic chloride. The cationic complexes Rh(P⁀P)₂ +X- were prepared from the Rh(P⁀P)₂ Cℓ species by adding AgX[X=SbF₆,PF₆,BF₄] . Reaction of the chloro complexes with borohydride has yielded the hydrides, H Rh(P⁀P)₂, for the n=2 and 3 diphosphines, and for (+)-diop. ¹H and ³¹P nmr, as well as visible spectral data, are presented: a solvent-dependent deshielding of ortho protons of the phenyl groups is observed in some of the complexes, and the ligand CH₂ protons are coupled to the rhodium in the Rh(Ph PCI^PPh^^ cation; the P atom in this bis(diphenylphosphino) ligand shows an unusual highfield shift on coordination to rhodium. Preliminary kinetic data for catalytic hydrogenation of methylene succinic0 acid or itaconic acid (IA) show that the cationic and hydrido complexes are more active than the corresponding chloro complexes, and that activity generally increases with increasing chain length of the diphosphine. The rhodium-bis(diop) complexes efficiently catalyze the asymmetric hydrogenation of a number of prochiral substrates, optical purities of >90% being obtained in the hydrogenation of N-acylaminoacrylic acids. Steric factors at the olefinic bond, and coordination of the -NHCOR group through the "^C=0 moiety, seem important in determining the hydrogenation rates. The rates are slower in the more strongly coordinating DMA compared to n-butanol-toluene mixtures. The solvent medium has little effect on the +degree of asymmetric induction, when using thre Rh[(+)-diop]2^ or HRh[(+)-diop]2 complexes, but reversal of product configuration is observed when using the Rh[(+)-diop]^Cl complex in DMA or in n-butanol-toluene mixtures. An unusual increase in optical purity of the product with increasing temperature has been observed in the hydrogenation of IA. Detailed kinetic and spectroscopic studies on the hydrogenation of IA catalyzed by HRh[(+)-diop] are explained in terms of a mechanism involving the formation of a metal alkyl via coordination of the olefinic substrate, followed by reaction with H2 to yield the saturated product (S.P.) and regenerated catalyst (equations [l]-[3]). A monodentate diop(diop*) is invoked: HRh(diop)2 _ HRh(diop)(diop*) [1] HRh(diop) (diop*) + olefin k Rh(diop) (diop*) (alkyl) [2] Rh(diop)(diop*)(alkyl) + > HRh(diop)(diop*) + S.P. [3] The initial hydride catalyst is slowly decomposed by protons of the acidic substrate to give Rh(diop)2+. To avoid this complication, a mechanistic study was carried out on the HRh(diop)2"Styrene-H2 system, which was found to proceed via the same mechanism as outlined in equations [l]-[3], A mechanistic study on the Rh(diop)2+BF^ -catalyzed hydrogenation of IA shows that the reaction proceeds mainly via the 'hydride' route: Rh(diop)2+ + H2 ^ Rh(diop)2H2+ [4] Rh(diop)2H2+ + IA v=^Rb(diop) (diop*) (H)2(IA)+ [5] Rh(diop) (diop*) (H)2(IA)+ > Rh(diop)2+ + S.P. [6] A complete inhibition of the hydrogenation by small amounts of added diop(diop:Rh>0.2) is tentatively attributed to formation of an inactive polymeric species: nRh(diop)2H2+ + diop > [Rh(diop)(diop*)H2+]n [7] The forward step of Reaction [4] was studied in detail in the absence of olefinic substrate. Spectroscopic and kinetic data are best explained in terms of dihydride formation via the consecutive reactions outlined in equation [8]: Rh(diop)„+ s . •> Rh(diop)(diop*)S+ ——• Rh(diop) (diop*) (H) „S+ [8] Rh(diop)2H2+ The dehydrogenation reaction was also studied. The reactions of [Rh(P~P)2]A complexes (A=C£,BF4) with C0,C>2,H2 and HC&(g) yield several new complexes. Thus the [Rh(P P)2XY] BF^ complexes rs rs r\ (P P = dpm,dpp;XY=CO, P P=dpm,dpe,dpp;XY=02, P P=dpp, (+)-diop: XY=H2, and rs P P=dpm,dpe,dpp;XY=HC&) were isolated and characterized. The solution 31 structures were determined using especially variable temperature P nmr spectroscopy. The formally six-coordinate rhodium(III) dioxygen and the dihydrido complexes were assigned cis geometries, whereas the HC£ complexes were more fluxional and cis geometries could only be assigned with certainty to the dpp complex; for dpm and dpe complexes, the limiting spectra could not be achieved even at -60°C. For the five-coordinate rhodium(I) CO complexes, the dpp complex has been assigned a TBP structure but the dpm complex is fluxional even at -60°C. Some stopped-flow kinetic data are presented for the addition of CO, 02, and B.^ to the Rh(P P>2 complexes. For the dpp system, the rate increased in the order CO>H2>02, although the reactions are not simple 1:1 single step additions, solvated species probably playing an important role (cf. equation [8]). / Science, Faculty of / Chemistry, Department of / Graduate

Efficient preparative routes to several new rhodium complexes and some iridium compounds containing sulfoxide ligands are described. Chiral sulfoxide complexes of rhodium were tested as possible catalysts for the homogeneous asymmetric hydrogenation of prochiral olefins. Also tested were chiral sulfoxide-iridium complexes as potential catalysts for H2 transfer from isopropanol to prochiral olefins and ketones. The sulfoxides used include: the monodentate ligands dimethyl (DMSO), tetramethylene (TMSO), di-n-propyl (NPSO), methyl phenyl (MPSO), and diphenyl sulfoxide (DPSO); the monodentate chiral ligands (+)-(R)-methyl-p-tolyl sulfoxide (MPTSO), (+)-(R)-t-butyl-p-tolyl sulfoxide (TBPTSO), (-)-(S)-o-tolyl-p-tolyl sulfoxide (OTPTSO), and (+)-(S)-2-methylbutyl-(S,R)-methyl sulfoxide (MBMSO); and the potentially chelating ligands meso-l,2-bis(methyl sulfinyl)ethane (MSE), (R,R)-1,2-bis(p-tolyl sulfinyl)ethane (PTSE), and (-)-(2R,3R)-2,3-0-isopropylidene-2,3-dihydroxy-1,4-bis(methyl sulfinyl)butane (DIOS). Displacement of the labile acetone ligand from [Rh(diene)(PPh₃) (acetone)]A (diene=l,5-cyclooctadiene (COD), norbornadiene (NBD); A=PF₆ ⁻, SbF₆ ⁻ ) allows facile coordination of dialkyl or diaryl sulfoxides, and [Rh(diene)(PPh₃)L]⁺ complexes (L=DMSO,TMSO,NPSO,MBMSO,MPSO,MPTSO, and TBPTSO) have been synthesized; compounds with L=AsPh₃, py and (CO)₂ also form. Diaryl sulfoxides and DIOS coordinate, but no solids were isolated. The upfield shifts of the sulfoxide resonances (¹H nmr), reflecting shielding by the adjacent phenyl groups of PPh₃, and the decrease in v(SO) on coordination, are indicative of O-bonding in all cases. NMR data on the olefinic diene protons suggest the occurrence of some disproportionation of the mixed ligand complexes to [Rh(diene) (PPh₃)₂]⁺ and [Rh(diene)(L)2]⁺ depending on L, and the presence of 3-coordinate, and 5-coordinate (for diene=NBD only) intermediates. The hydrogenation of itaconic acid using catalysts with L=R-MPTSO or DIOS resulted in no asymmetric induction in the a-methyl succinic acid product because of disproportionation and catalysis via the bis(triphenylphosphine) system. Efficient hydroformylation of 1-alkenes is effected using [Rh(diene) (PPh₃)(CO)₂j⁺ as catalyst precursors. Aqueous isopropanol solutions of RhCl₃-3H₂O on treatment with sulfoxides provide an efficient route to RhCl₃L₃ complexes (L=DMSO, R-MPTSO,MPSO,TMSO) that contain in solution, at least for the first three systems, two S-bonded sulfoxides trans to a chloride, and an 0-bonded ligand. The 0-bonded sulfoxide is displaced by amides, amine oxides, and phosphine oxides to give mer- RhCl₃ (DMSO)₂(OL) complexes. The DMSO cis to OL in RhCl₃DMSO)₂(OL) or RhCl₃ (DMSO)₃(OL) can be identified in the nmr by using the ring current shielding effects of OPPh₂Me. RhCl₃L₃ react with H₂ (1:1) in base promoted reactions to yield Rh(I) presumably via undetected Rh(III)-H species. RhCl₃.3H₂O reacts with DPSO in isopropanol to give Rh(I) as the chloride-bridged species [RhCl(DPSO)₂]₂. The reaction with NPSO gives a Rh(I) dimer (indirect evidence) and a Rh(III) product, isolated as [H(NPSO)₂][RhCl₄(NPSO)₂] containing a symmetrical hydrogen-bridged cation. A crystal structure of trans-[H(DMSO)₂] [RhCl₄(DMSO)₂] reveals the short oxygen-oxygen distance (~2.45Å) in the cation expected for strong H-bonds. Such cations display intense v[sub a] (OHO) bands at 1700- 1100 and 900-600 cm⁻¹. The air-sensitive complexes [RhCl(C₈H₁₄)(DPSO)]₂, [RhCl(DMS0)₂]₂, [RhCl(DIOS)₂]₂ and [RhCl(MPSO)(PPh₃)]₂, isolated from [RhCl(cyclooctene)₂]₂/ ligand solutions, contain very labile Rh-S bonds that do not appear to involve Rh(dπ)+S (d-π) backbonding. Attempts at generating hydride complexes by oxidative addition of H₂ or HCl to Rh(I) resulted normally in either metal formation or sulfoxide reduction; even in the presence of prochiral olefins these complications occurred rather than catalytic asymmetric hydrogenation. The compound [Rh(MSE) ₂]PF₆ was isolated from the reaction of H₂ with [Rh(NBD) ₂]PF₆, and 2 MSE in alcohol solutions. The compounds mer-IrCl₂(H)(DMS0)₃ with trans chlorides, and mer-IrCl(H)₂(DMSO)₃ with cis hydrides, were obtained from oxidative addition reactions involving HCl and H₂, respectively, with [IrCl(C₈H₁₄)₂]₂ in DMSO. The former catalyzes the efficient selective reduction of α,β-unsaturated aldehydes to the unsaturated alcohols. Attempts at asymmetric synthesis using as catalysts IrCl₃H₂0/chiral sulfoxide mixtures failed. A simple bent M<-O=L vibrational model is used to estimate from v(M0) and v(S0) the force constants F[sub MO] and F[sub OL] using data for seventy 0-bonded DMSO, DMSO-D₆, and TMSO complexes of several metals. The correlation F[sub OL]=-(1.24±0.12)F[sub MO].+(8.78±0.12) mdyne/Å appears to hold for all metal complexes excepting those of group IVA and VA elements. / Science, Faculty of / Chemistry, Department of / Graduate

Chapter 1 deals with the reaction of [Rh(acac)(PMe3)2] with para-substituted 1,4-diphenylbuta-1,3-diynes at room temperature, in which a complex containing a bidentate organic fulvene moiety, composed of two diynes, σ-bound to the rhodium center is formed in an all-carbon [3+2] type cyclization reaction. In addition, a complex containing an organic indene moiety, composed of three diynes, attached to the rhodium center in a bis-σ-manner is formed in a [3+2+3] cyclization process. Reactions at 100 °C reveal that the third diyne inserts between the rhodium center and the bis-σ-bound organic fulvene moiety. Furthermore, the formation of a 2,5- and a 2,4-bis(arylethynyl)rhodacyclopentadiene is observed. The unique [3+2] cyclization product was used for the synthesis of a highly conjugated organic molecule, which is hard to access or even inaccessible by conventional methods. Thus, at elevated temperatures, reaction of the [3+2] product with para-tolyl isocyanate led to the formation of a purple organic compound containing the organic fulvene structure and one equivalent of para-tolyl isocyanate. The blue and green [3+2+3] complexes show an unusually broad absorption from 500 – 1000 nm with extinction coefficients ε of up to 11000 M-1 cm-1. The purple organic molecule shows an absorption spectrum similar to those of known diketopyrrolopyrroles. Additionally, the reaction of [Rh(acac)(PMe3)2] with para-tolyl isocyanate was investigated. A cis-phosphine complex of the form cis-[Rh(acac)(PMe3)2(isocyanate)2] with an isocyanate dimer bound to the rhodium center by one carbon and one oxygen atom was isolated. Replacing the trimethylphosphine ligands in [Rh(acac)(PMe3)2] with the stronger σ-donating NHC ligand Me2Im (1,3-dimethylimidazolin-2-ylidene), again, drastically alters the reaction. Similar [3+2] and [3+2+3] products to those discussed above could not be unambiguously assigned, but cis- and trans-π-complexes, which are in an equilibrium with the two starting materials, were formed. Chapters 2 is about the influence of the backbone of the α,ω-diynes on the formation and photophysical properties of 2,5-bis(aryl)rhodacyclopentadienes. Therefore, different α,ω-diynes were reacted with [Rh(acac)(PMe3)2] and [Rh(acac)(P(p-tolyl)3)2] in equimolar amounts. In general, a faster consumption of the rhodium(I) starting material is observed while using preorganized α,ω-diynes with electron withdrawing substituents in the backbone. The isolated PMe3-substituted rhodacyclopentadienes exhibit fluorescence, despite the presence of the heavy atom rhodium, with lifetimes τF of < 1 ns and photoluminescence quantum yields Φ of < 0.01 as in previously reported P(p-tolyl)-substituted 2,5-bis(arylethynyl)rhodacyclopentadienes. However, an isolated P(p-tolyl)-substituted 2,5-bis(aryl)rhodacyclopentadiene shows multiple lifetimes and different absorption and excitation spectra leading to the conclusion that different species may be present. Reaction of [Rh(acac)(Me2Im)2] with dimethyl 4,4'-(naphthalene-1,8-diylbis(ethyne-2,1-diyl))dibenzoate, results in the formation of a mixture trans- and cis-NHC-substituted 2,5-bis(aryl)rhodacyclopentadienes. In chapter 3 the reaction of various acac- and diethyldithiocarbamate-substituted rhodium(I) catalysts bearing (chelating)phosphines with α,ω-bis(arylethynyl)alkanes (α,ω-diynes), yielding luminescent dimers and trimers, is described. The photophysical properties of dimers and trimers of the α,ω-diynes were investigated and compared to para-terphenyl, showing a lower quantum yield and a larger apparent Stokes shift. Furthermore, a bimetallic rhodium(I) complex of the form [Rh2(ox)(P(p-tolyl)3)4] (ox: oxalate) was reacted with a CO2Me-substituted α,ω-tetrayne forming a complex in which only one rhodium(I) center reacts with the α,ω-tetrayne. The photophysical properties of this mixed rhodium(I)/(III) species shows only negligible differences compared to the P(p-tolyl)- and CO2Me-substituted 2,5-bis(arylethynyl)rhodacyclopentadiene, previously synthesized by Marder and co-workers. / Kapitel 1 beschäftigt sich mit der Umsetzung von [Rh(acac)(PMe3)2] mit zwei Äquivalenten para-substituierten 1,4-Diphenylbuta-1,3-diins bei Raumtemperatur. Dabei bildete sich ein Komplex, welcher eine organische Fulveneinheit, bestehend aus zwei Diinen und verbunden über zwei σ-Bindungen mit dem Rhodiumzentralatom, besitzt. Diese Verbindung bildet sich in einer „all-carbon“ [3+2] ähnlichen Zyklisierungsreaktion. Ebenso konnte aus derselben Reaktion ein Komplex mit einer Indeneinheit, bestehend aus drei Diinen, welche durch zwei σ-Bindungen mit dem Rhodiumzentralatom verbunden sind, isoliert und charakterisiert werden. Diese Verbindung bildet sich in einer „all-carbon“ [3+2+3] ähnlichen Zyklisierungsreaktion. Experimente bei 100 °C zeigen, dass sich das zusätzliche dritte Diin zwischen dem Rhodiumzentralatom und der organischen Fulveneinheit einfügt. Zusätzlich konnte die Bildung von 2,4- und 2,5-Bis(arylethinyl)rhodazyklopentadienen bei 100°C beobachtet werden. Diese seltene [3+2] Zyklisierungsreaktion kann benutzt werden um konjugierte, organische Moleküle darzustellen, welche sonst nur schwer oder gar nicht mit bisher bekannten Synthesemethoden zugänglich sind. In der Umsetzung des [3+2] Komplexes mit para-Tolylisocyanat bei 80 °C konnte ein violetter, rein organischer Feststoff erhalten werden, bestehend aus der organischen Fulveneinheit und einem Äquivalent para-Tolylisocyanat. Die blauen und grünen [3+2+3] Komplexe zeigen unter anderem eine ungewöhnliche breite Absorption von 500 – 1000 nm mit einem Extinktionskoeffizienten von bis zu 11000 M-1 cm-1. Die violette, rein organische Verbindung zeigt ein Absorptionsspektrum ähnlich zu bereits bekannten Diketopyrrolopyrrolen. Auch wurde die Reaktion von [Rh(acac)(PMe3)2] mit para-Tolylisocyanat untersucht. Es konnte ein cis-phosphan Komplex, bei dem ein para-Tolylisocyanat-Dimer über ein Kohlenstoff- und ein Sauerstoffatom an das Rhodiumzentralatom koordiniert, isoliert und charakterisiert werden. Substitution des Trimethylphosphans im Rh(I)-Präkursors durch einen NHC Liganden, nämlich Me2Im (1,3-dimethylimidazolin-2-yliden) führt zu einem unterschiedlichen Reaktionsverlauf. Ähnliche [3+2] und [3+2+3] Komplexe konnten nicht zweifelsfrei bestätigt werden, dafür konnte aber gezeigt werden, dass sich in der Reaktion bildende cis- und trans-Komplexe im Gleichgewicht mit den verwendeten Startmaterialien befinden. Im zweiten Kapitel dieser Arbeite wurde der Einfluss des Rückgrats von α,ω-bis(arylethynyl)alkanen (α,ω-Diine) auf die Bildung und die photophysikalischen Eigenschaften von 2,5-Bis(aryl)rhodazyklopentadienen untersucht. Dazu wurden mehrere α,ω-Diine mit unterschiedlichem Rückgrat synthetisiert und diese mit [Rh(acac)(PMe3)2] und [Rh(acac)(P(p-tolyl)3)2] in äquimolaren Mengen reagiert. Es konnte ein schnellerer Verbrauch des Rh(I)-Präkursors bei der Verwendung von vororganisierten α,ω-Diinen mit elektronenziehenden Substituenten am Rückgrat festgestellt werden. Die PMe3-substituierten Rhodazyklopentadiene zeigen Fluoreszenz, trotz der Anwesenheit eines Schwermetalls. Lebenszeiten von τF < 1 ns und Quantenausbeuten von Φ < 0.01, ähnlich wie in P(p-tolyl)-substituierten 2,5-Bis(arylethynyl)rhodazyklopentadienen wurden beobachtet. Bei einem isolierten P(p-tolyl)-substituierten 2,5-Bis(aryl)rhodazyklopentadien konnten mehrere Lebenszeiten, wie auch unterschiedliche Absorptions- und Anregungsspektren detektiert werden, was zu der Schlussfolgerung führt, dass in Lösung mehrere Spezies vorhanden sind. Die Reaktion von [Rh(acac)(Me2Im)2] mit Dimethyl 4,4'-(naphthalen-1,8-diylbis(ethyn-2,1-diyl))dibenzoat führt zur Bildung einer Mischung aus trans- und cis-NHC-substituierter 2,5-Bis(aryl)rhodazyklopentadienen. Im dritten Kapitel, wurde die Bildung lumineszenter Dimere und Trimere aus der Umsetzung von verschiedenen α,ω-Diinen mit katalytischen Mengen verschiedener acac- und diethyldithiocarbamat-substituierter Rhodium(I)-Katalysatoren mit (chelatisierenden) phosphanen untersucht. Anschließend wurden die photophysikalischen Eigenschaften der Dimere und Trimere untersucht und mit para-Terphenyl verglichen. Dabei wurden ähnliche Lebenszeiten, eine geringere Quantenausbeute wie auch größere Stokes-Verschiebungen der Dimere und Trimere im Vergleich zu para-Terphenyl gefunden. Auch wurde die Reaktion zwischen einem bimetallischen Rhodium Komplex [Rh2(ox)(P(p-tolyl)3)4] (ox: oxalat) und einem CO2Me-substituiertem α,ω-bis(arylbutadiynyl)alkan (α,ω-Tetrain) untersucht. In dieser Umsetzung reagierte nur eine der beiden möglichen Rhodium(I)-zentren mit dem α,ω-Tetrain unter Bildung eines 2,5-Bis(arylethynyl)rhodazyklopentadiens. Die photophysikalischen Eigenschaften dieser gemischten Rhodium(I)/(III)-Spezies zeigt nur marginale unterschiede, verglichen mit einem mononuklearen P(p-tolyl)- und CO2Me-substituiertem 2,5-Bis(arylethynyl)rhodazyklopentadiens, welches zuvor im Arbeitskreis Marder schon synthetisiert wurde.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering Johannesburg, 2018 / The use of austenitic stainless steels in harsh environments at elevated temperatures has increasingly become a global problem, these alloys can fail unpredictably when subjected to tensile stresses and chlorides. Hence the study was focused on understanding the environmentally assisted cracking of Ru enriched laser alloyed layers on 304L stainless steel in a corrosive environment at elevated temperatures. The Ru composition of laser alloyed samples was 0, 0.96, 1.96, 4.74 and 9.2 wt%. Microstructural analysis and microhardness measurements were performed in order to understand the grain orientation and resistance to indentation respectively. The bend beam SCC test was conducted by stressing the samples to 350 MPa and exposing them to 50 ppm sodium chloride with 10 ppm dissolved oxygen at 160°C for 172 hours. The results revealed a significant improvement in the SCC resistance. The samples with lower Ru content (0, 0.98 and 1.96 wt%) were less susceptible to SCC when compared to as-received 304L stainless steel. Cracks initiated from pits and propagated transgranularly on the alloyed layer. The crack growth rate decreased as the Ru content was increased. The samples with 4.74 and 9.2 wt% Ru were immune to SCC. Electrochemical test results showed improved corrosion resistance when the Ru level was increased to 1.96 wt%. Thereafter, there was a gradual increase in corrosion rates for samples with 4.74 and 9.2 wt% Ru. However, these corrosion rates were lower when compared to as-received 304L stainless steel. Another SCC test was conducted to investigate fractography of vacuum remelted samples alloyed with Ru. The results showed ductile failure for most of the samples and the maximum stress threshold of 580 MPa was archived on samples with 1.07 wt% Ru. There was a sudden increase in failure time, % elongation and % reduction in area when the Ru content was increased to 1.07 wt%. In essence, laser surface alloying 304L stainless steel with higher Ru content (more than 2wt%) improves SCC resistance, but does not improve the general corrosion resistance, therefore a careful selection for any application is necessary. However, the cost analysis revealed the laser surface alloying of 304L stainless steel with Ru to be more efficient over other corrosion resistant materials. / MT 2018