This thesis covers an investigation of the use of pyrazolyl palladium complexes as Heck and Suzuki coupling catalysts. It is organised into four chapters. Chapter 1 is a review of the relevant literature and therefore does not cover any new work. Chapters 2 and 3 describe the synthesis and characterization of palladium complexes and testing as Heck and Suzuki coupling catalysts respectively. Chapter 4 is a summary of conclusions and future work. The subsequent section provides the main findings in chapters 2, 3 and 4. Chapter 2 is on the synthesis and characterization of palladium complexes that were used to catalyse the Heck and the Suzuki coupling reactions. The poly(pyrazol-1-ylmethyl)benzene ligands were prepared from reactions in which bis(bromomethyl)benzene with bromo substituents in different positions were reacted with either 3,5-dimethylpyrazole or 3,5-ditertiarybutylpyrazole. The products formed from these reactions were: {(3,5-Me2pzCH2)4-1,2,4,5-C6H4} (L1), {(3,5-Me2pzCH2)2}2-1,4-C6H4 (L2), {(3,5-tBu2pzCH2)2-1,4-C6H4} (L3), {(3,5-Me2pzCH2)2}2-1,3-C6H4 (L4), and {(3,5-Me2pzCH2)2}2-1,2-C6H4 (L4). Compounds L1-L5 were subsequently used to prepare their corresponding palladium complexes C1-C8, by reacting the poly(pyrazol-1-ylmethyl)benzene ligands L1-L5 with [PdCl2(NCMe)2] or [PdClMe(COD)] to form the tetranuclear palladium complex [{Pd2Cl(3,5-Me2pzCH2)4-1,2,4,5-C6H4}2] (C1), or dinuclear palladium complexes [{Pd2(μ-Cl)2X2(3,5-Me2pzCH2)2-1,4-C6H4}] (X = Cl (C2), Me (C6)), [{Pd2(μ-Cl)2Cl2(3,5-tBu2pzCH2)2-1,4-C6H4}] (C3), [{Pd2ClX(3,5-Me2pzCH2)2-1,3-C6H4}2] (X = Cl (C4), Me (C8), [{Pd2ClX(3,5-Me2pzCH2)2-1,2-C6H4}2] {X = Cl (C5), Me (C7)}, All the compounds were characterized by multinuclear NMR and elemental analysis. The structures of C1, C5 and C7 were confirmed by single crystal X-ray structural analysis. Chapters 3 and 4 describe the use of new palladium complexes prepared in this project as catalysts in Heck and Suzuki cross coupling reactions. The complexes efficiently catalysed the Heck coupling reactions which involved the coupling of iodobenzene and butylacrylate to produce trans-butyl cinnamate at 80 oC, with over 80 % conversion found within 6 h, and over 90 % within 24 h. The Suzuki coupling reactions between iodobenzene and phenylboronic acid were also performed at 80 oC. The Suzuki coupling reactions were not as efficient as the Heck coupling reactions and conversions of more than 70 % could only be reached after 24 h. Complex C6 gave the highest conversions in both the Heck and the Suzuki coupling reactions, with Heck coupling conversions of 100 % within 6 h and Suzuki coupling conversion of 73 % within 24. The major significant finding in using these palladium complexes in the two coupling reactions is that they perform both reactions at a much lower temperature (80 oC) compared to the normal temperatures of 120-160 oC used in such reaction. / Professor James Darkwa

M.Sc. / [AuCl(PPh3)] was reacted with mixed thiols in the presence of silver(I) oxide, resulting in complexes of the type [Au(SC6H4X)(PPh3)] X= Cl, NH2,CH2, forming silver chloride as a by-product. In addition to the above series [Au(SCH2(C6H4)3(2-C6H5(C6H4N)] was prepared via a different route, where [AuCl3(2-C6H5(C6H4N)] was reacted with benzyl mercaptan under reflux in the presence of silver(I) oxide for 3 h, forming silver chloride as a by-product. Palladium complex [PdCl2(2-C6H5(C6H4N)] was prepared by reacting [PdCl2(MeCN)] with 2-phenylpyridine at room temperature for 2 h. All complexes were characterized by 1H, 13C, 31P{H} NMR, IR, mass spectrometry and elemental analysis. Characterization of the starting materials [AuCl3(2-C6H5(C6H4N)] and [PdCl2(2- C6H5(6H4N)] by single crystal X-ray diffraction confirmed their chemical formula. All complexes were reacted with sulfur dioxide (SO2) and the reactions were monitored by electrochemistry and UV-vis spectroscopy. The electrochemical study of the complexes, using cyclic voltammetry (CV) and Osteryoung square wave voltammetry (OSWV), showed one anodic peak, which is due to gold(I/III) and an unresolved peak due to thiolate ligand. Upon bubbling of SO2 to the complexes, there was an immediate change of colour from clear to yellow, the CV results showing an increase in current of the gold(I/III) peak. UV-vis spectroscopy studies showed a shift of peak form 250-286 nm, upon bubbling of SO2 to complexes.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

M.Sc. (Chemistry) / This study deals with the synthesis of nitrogen-donor pyrazole- and pyrazolylethylamine compounds, their reactions with palladium(II) and nickel(II) precursors to form complexes and the applications of theses palladium(II) and nickel(II) complexes as catalysts for ethylene oligomerization reactions and reactions of higher α-olefins in Friedel-Crafts alkylation of aromatic solvents. A series of ligands, 3,5-di-tert-butyl-1H-pyrazole (L3), 3,5-diphenyl-1H-pyrazole (L4), 5-phenyl-3-(trifluoromethyl)-1H-pyrazole (L5) were synthesized using appropriate amounts of diketones and hydrazine hydrate; while ligands, 2-(1H-pyrazol-1-yl)ethylamine (L6), 2-(3,5-dimethyl-1H-pyrazol-1-yl)-ethylamine (L7), 2-(3,5-di-tert-butyl-1H-pyrazol-1-yl)-ethylamine (L8), 2-(3,5-diphenyl-1H-pyrazol-1-yl)-ethylamine (L9) and 2-(5-phenyl-3-(trifluoromethyl)-1H-pyrazol-1-yl)ethylamine (L10) were prepared via the N sp3 alkylation of the corresponding pyrazoles with bromoethylamine Reactions of L1-L5 with [PdCl2(CNMe)2] formed five complexes of general formula [PdCl2 (L)2] {L = L1 (2.1), L2 (2.2), L3 (2.3), L4 (2.4) and L5 (2.5)}. Similarly [NiBr2(DME)] formed five complexes of general formula [NiBr2(L)2] {L = L1(2.6), L2 (2.7), L3 (2.8), L4 (2.9) and L5 (2.10)}. Complexes 2.1-2.10 were synthesized in a 2:1 mole ratio of ligand and metal precursor. Reactions of L6-L10 with [PdCl2(MeCN)2] yielded complexes 3.1-3.5 respectively. Ligands L6-L10 were also complexed with NiCl2.6H2O to give complex 3.6 while [NiCl2(DME)] and [NiBr2(DME)] gave complexes 3.7-3.8 and 3.9-3.13 respectively...

M.Sc. / This study describes the synthesis of pyrazolyl palladium and nickel complexes and their applications as catalysts for the co-polymerization of olefins with carbon monoxide and also as ethylene oligomerization catalysts. A series of compounds, 2-(3,5-dimethyl-pyrazol-1-yl)-ethyl]-pyridin-2-ylmethylene-imine (L1), 2-(3,5-di-tert-butyl-pyrazol-1-yl)-ethyl]-pyridin-2-ylmethylene-imine (L2), 2-(3,5-dimethyl-pyrazol-1-yl)-ethyl]-thiophen-2-ylmethylene-imine (L3), 2-(3,5-di-tert-butyl-pyrazol-1-yl)-ethyl]-thiphen-2-ylmethylene-imine (L4), 2-(3,5-dimethyl-pyrazol-1-yl)-ethyl]-5-bromothiophen-2-ylmethylene-imine (L5), 2-(3,5-di-tert-butyl-pyrazol-1-yl)-ethyl]-2bromothiophen-2-ylmethylene-imine (L6), 2-(3,5-dimethyl-pyrazol-1-yl)-ethyl]-pyrrol-2-ylmethylene-imine (L7) and 2-(3,5-di-tert-butyl-pyrazol-1-yl)-ethyl]-pyrrol-2-ylmethylene-imine (L8)] were prepared via Schiff base condensation of the appropriate amines and aldehydes. Reactions of L1-L6 and L8 with [PdClCH3(cod)] formed six complexes of general formula [PdClCH3(L)] {L = L1 (1), L2 (2), L3 (3), L4 (4), L5 (5) and L6 (6)} and [Pd(L8)2] (7). Complexes 1-6 were converted to the cationic compounds [PdCH3(L)]BAr4 {L = L1 (8), L2 (9), L3 (10), L4 (11), L5 (12) and L6 (13)} by the reaction of compounds 1-6 with the halide abstractor Na[BAr4] (where Ar = (3,5-(CF3)2C6H3) in a 1:1 mole ratio. For compounds 8 and 9 the cationic species were stabilized by the coordination of the pyrazolyl units of the ligands, which were uncoordinated in the parent palladium complexes 1 and 2. The cationic complexes 10-13, however, were stabilized by v coordination of NCCH3 to the palladium centre. Complexation of L1, L2, L5 and L6 with [PdCl2(NCCH3)2] gave the palladium dichloro complexes [PdCl2(L)], {L = L1 (14), L2 (15), L5 (16), and L6 (17)}. Compounds L1, L2, L7 and L8 were reduced to form compounds L9-L12 respectively and were reacted with [NiBr2DME] to form complexes [NiBr2(L)] {L = L9 (18), L10 (19), L11 (20) and L12 (21).