This thesis presents a detailed theoretical/computational analysis using quantum chemistry to investigate the thermochemistry and reaction mechanisms of palladacycles that underpin experimental observations. The thesis begins by establishing a suitable computational methodology for the study of pincer palladacycles. It was found that Density Functional Theory (DFT) was suitable for the accurate reproduction of geometric structures and energetics by comparing a range of commonly used density functionals and basis sets with the X-ray crystal structures of symmetric pincer palladacycles. The detailed electronic structure of several pincer palladacycles was investigated using Complete Active Space Self-Consistent Field method (CASSCF) and it was shown that the dominant configuration was larger than 0.96, indicating that the ground state electronic structure has significant single-reference character. DFT was used to investigate the stability of symmetrical pincer palladacycles, and then by changing the donor ligand, unsymmetrical pincer palladacycles. The pincer palladacycle formation was investigated and it was found that the barrier to C-H activation was dependent on the ligand arm of the pincer that coordinates to PdCl2. Topological analysis was performed using Quantum Theory of Atoms In Molecules (QTAIM) for determining the strength and nature of the Pd and donor atom interactions, showing that the bond strength depends on the type of donor atom and trans influence in the pincer palladacycles. The mechanism for Pd(0) formation from both symmetrical and unsymmetrical pincer palladacycle pre-catalysts for catalysis in Suzuki-Miyaura carbon-carbon cross-coupling reactions was studied, and then with the introduction of base and the effect of solvent. It was shown that the key steps are transmetallation and reductive elimination processes, and differences in the overall Gibbs free energy and transmetallation barrier provide an explanation for observed catalytic activity. This has been in conjunction with experimental chemists. Finally, the functionalisation of benzodiazepines was investigated in three conditions; with Pd(II)/Ru(II)-catalysts, with Pd(II)-catalysts and without catalyst. It was found that the Ru(II) photocatalyst with Pd(II)-catalyst is the best condition for functionalisation on benzodiazepines with the lowest energy barrier.

Investigation of catalytic main-group bond forming reactions is the basis of this dissertation. Coupling of group 14 and 15 elements by several different methods has been achieved. The influence of Si–N heterodehydrocoupling on the promotion of α-silylene elimination was realized. Efficient Si–N heterodehydrocoupling by a simple, earth abundant lanthanide catalyst was demonstrated. Significant advances in hydrophosphination by commercially available catalysts was achieved by photo-activation of a precious metal catalyst. Exploration of (N3N)ZrNMe2 (N3N = N(CH2CH2NSiMe3)33–) as a catalyst for the cross-dehydrocoupling or heterodehydrocoupling of silanes and amines suggested silylene reactivity. Further studies of the catalysis and stoichiometric modeling reactions hint at α-silylene elimination as the pivotal mechanistic step, which expands the 3p elements known to engage in this catalysis and provides a new strategy for the catalytic generation of low-valent fragments. In addition, silane dehydrocoupling by group 1 and 2 metal bis(trimethylsilyl)amide complexes was investigated. Catalytic silane redistribution was observed, which was previously unknown for d0 metal catalysts. La[N(SiMe3)2]3THF2 is an effective pre-catalyst for the heterodehydrocoupling of silanes and amines. Coupling of primary and secondary amines with aryl silanes was achieved with a loading of 0.8 mol % of La[N(SiMe3)2]3THF2. With primary amines, generation of tertiary and sometimes quaternary silamines was facile, often requiring only a few hours to reach completion, including new silamines Ph3Si(nPrNH) and Ph3Si(iPrNH). Secondary amines were also available for heterodehydrocoupling, though they generally required longer reaction times and, in some instances, higher reaction temperatures. By utilizing a diamine, dehydropolymerization was achieved. The resulting polymer was studied by MS and TGA. This work expands upon the utility of f-block complexes in heterodehydrocoupling catalysis. Stoichiometric and catalytic P–E bond forming reactions were explored with ruthenium complexes. Hydrophosphination of primary phosphines and activated alkenes was achieved with 0.1 mol % bis(cyclopentadienylruthenium dicarbonyl) dimer, [CpRu(CO)2]2. Photo-activation of [CpRu(CO)2]2 was achieved with a commercially available UV-A 9W lamp. Preliminary results indicate that secondary phosphines as well as internal alkynes may be viable substrates with this catalyst. Attempts to synthesize ruthenium phosphinidene complexes for stoichiometric P–E formation have been met with synthetic challenges. Ongoing efforts to synthesize a ruthenium phosphinidene are discussed. The work in this dissertation has expanded the utility of metal-catalyzed main-group bond forming reactions. A potential avenue for catalytic generation low-valent silicon fragments has been discovered. Rapid Si–N heterodehydrocoupling by an easily obtained catalyst has been demonstrated. Hydrophosphination with primary phosphines has been achieved with a commercially available photocatalyst catalyst, requiring only low intensity UV light.

Electronic and steric parameters for square planar NiN2S2 complexes as bidentate, S-donor ligands have been established. According to the (CO) stretching frequencies and associated computed Cotton-Kraihanzel force constants of (NiN2S2)W(CO)4 adducts, a ranking of donor abilities and a comparison with classical bidentate ligands are as follows: Ni(ema)= > { [NiN2S2]0 } > bipy phen > Ph2PCH2CH2PPh2 > Ph2PCH2PPh2. In addition, we have demonstrated that the NiN2S2 ligands are hemilabile as evidenced from CO addition to (NiN2S2)W(CO)4, which is in equilibrium with the resulting (NiN2S2)W(CO)5 species (Keq = 2.8 M-1, G = -1.4 kJ/mole at 50C). Complete NiN2S2 ligand displacement by CO-cleavage of the remaining W-S bond to form W(CO)6 was not observed, indicating that the remaining W-S bond is considerably strengthened upon ring-opening. Several new cluster compounds based on the NiN2S2 ligands bound to CuI, RhI, PdII and W0 are reported. Structural analysis of (NiN2S2)MLn complexes show a unique structural feature defined by the dihedral angle formed by the intersection of NiN2S2/WS2C2 planes; placing the NiN2S2 ligand in closer proximity to one side of the reactive metal center. This unique orientational feature of the NiN2S2 ligands in the series of bimetallic compounds contrasts with classical diphosphine or diimine ligands. The "hinge angle" ranges in value from 136 as in the (Ni-1*)W(CO)4 to 101 in the (Ni-1)Pd(CH3)(Cl) complexes. The rigidity of the SR hinge of the nickeldithiolate ligands suggests that they might be suitable for stereochemical and regioselective substrate addition to catalytically active metals such as RhI and PdII.. The structural as well as functional similarities of the acetyl CoA synthase enzyme (ACS) and a palladium-metal based industrial type catalyst led to the preparation of a [(Ni-1)Pd(CH3)]+ bimetallic complex. This complex facilitates CO and ethylene copolymerization to produce polyketone similar to conventional (diphosphine)Pd(X)2 catalysts. However, the diphosphine ligands produce more efficient catalysts as the electron-rich character of the NiN2S2 ligand favors the resting state of the catalyst, [(Ni-1)Pd(C(O)CH3)(CO)]+, over the reactive form (Ni-1)Pd(C(O)CH3)(2-C2H4)]+. An exploratory investigation with the Ni-Pd heterobimetallic showed that this complex also facilitated the C-S coupling reaction to form a thioester similar to the ACS enzyme.

Aluminum complexes, specifically those employing bulky ligand frameworks such as sal (sal = 2-[CH═N(2,6-iPr2-C6H3)]-4,6-tBu2-phenoxide) and alpha-diimine (alpha-diimine = [(2,6-iPr2-C6H3)N═C(Me)]2) derivatives are studied in various contexts. During ethylene polymerization with LCu(II) catalysts in the presence of methylaluminoxane (MAO), ligand (L) transfer is observed from the copper centre to the aluminum centre present in MAO. In the alpha-diimine case, an (imino-amido)AlMe2 complex is formed by alpha-diimine ligand transfer to aluminum followed by alkylation of one imino moiety in the ligand backbone. These ligand transfer products are then shown to be active as ethylene polymerization catalysts, bringing into question the role of the copper species. The (sal)AlMe2, (sal)AlMeCl and (imino-amido)AlMe2 complexes were also used as initiators in the ring-opening polymerization of epsilon-caprolactone. Polymerization was studied with and without addition of tert-butanol as a co-initiator to determine its role and necessity in the catalytic cycle. Finally, the (imino-amido)AlMe2 complex was also used as the starting complex in attempts at forming a mononuclear aluminum(I) target species. Reaction of (imino-amido)AlMe2 with excess I2 proved successful in forming the isolable precursor, (imino-amido)AlI2. Attempts at reducing (imino-amido)AlI2 with excess potassium were carried out in hopes of forming a very rare example of a mononuclear aluminum(I) species.

Aluminum complexes, specifically those employing bulky ligand frameworks such as sal (sal = 2-[CH═N(2,6-iPr2-C6H3)]-4,6-tBu2-phenoxide) and alpha-diimine (alpha-diimine = [(2,6-iPr2-C6H3)N═C(Me)]2) derivatives are studied in various contexts. During ethylene polymerization with LCu(II) catalysts in the presence of methylaluminoxane (MAO), ligand (L) transfer is observed from the copper centre to the aluminum centre present in MAO. In the alpha-diimine case, an (imino-amido)AlMe2 complex is formed by alpha-diimine ligand transfer to aluminum followed by alkylation of one imino moiety in the ligand backbone. These ligand transfer products are then shown to be active as ethylene polymerization catalysts, bringing into question the role of the copper species. The (sal)AlMe2, (sal)AlMeCl and (imino-amido)AlMe2 complexes were also used as initiators in the ring-opening polymerization of epsilon-caprolactone. Polymerization was studied with and without addition of tert-butanol as a co-initiator to determine its role and necessity in the catalytic cycle. Finally, the (imino-amido)AlMe2 complex was also used as the starting complex in attempts at forming a mononuclear aluminum(I) target species. Reaction of (imino-amido)AlMe2 with excess I2 proved successful in forming the isolable precursor, (imino-amido)AlI2. Attempts at reducing (imino-amido)AlI2 with excess potassium were carried out in hopes of forming a very rare example of a mononuclear aluminum(I) species.

Electronic and steric parameters for square planar NiN2S2 complexes as bidentate, S-donor ligands have been established. According to the (CO) stretching frequencies and associated computed Cotton-Kraihanzel force constants of (NiN2S2)W(CO)4 adducts, a ranking of donor abilities and a comparison with classical bidentate ligands are as follows: Ni(ema)= > { [NiN2S2]0 } > bipy phen > Ph2PCH2CH2PPh2 > Ph2PCH2PPh2. In addition, we have demonstrated that the NiN2S2 ligands are hemilabile as evidenced from CO addition to (NiN2S2)W(CO)4, which is in equilibrium with the resulting (NiN2S2)W(CO)5 species (Keq = 2.8 M-1, G = -1.4 kJ/mole at 50C). Complete NiN2S2 ligand displacement by CO-cleavage of the remaining W-S bond to form W(CO)6 was not observed, indicating that the remaining W-S bond is considerably strengthened upon ring-opening. Several new cluster compounds based on the NiN2S2 ligands bound to CuI, RhI, PdII and W0 are reported. Structural analysis of (NiN2S2)MLn complexes show a unique structural feature defined by the dihedral angle formed by the intersection of NiN2S2/WS2C2 planes; placing the NiN2S2 ligand in closer proximity to one side of the reactive metal center. This unique orientational feature of the NiN2S2 ligands in the series of bimetallic compounds contrasts with classical diphosphine or diimine ligands. The "hinge angle" ranges in value from 136 as in the (Ni-1*)W(CO)4 to 101 in the (Ni-1)Pd(CH3)(Cl) complexes. The rigidity of the SR hinge of the nickeldithiolate ligands suggests that they might be suitable for stereochemical and regioselective substrate addition to catalytically active metals such as RhI and PdII.. The structural as well as functional similarities of the acetyl CoA synthase enzyme (ACS) and a palladium-metal based industrial type catalyst led to the preparation of a [(Ni-1)Pd(CH3)]+ bimetallic complex. This complex facilitates CO and ethylene copolymerization to produce polyketone similar to conventional (diphosphine)Pd(X)2 catalysts. However, the diphosphine ligands produce more efficient catalysts as the electron-rich character of the NiN2S2 ligand favors the resting state of the catalyst, [(Ni-1)Pd(C(O)CH3)(CO)]+, over the reactive form (Ni-1)Pd(C(O)CH3)(2-C2H4)]+. An exploratory investigation with the Ni-Pd heterobimetallic showed that this complex also facilitated the C-S coupling reaction to form a thioester similar to the ACS enzyme.

With hundreds of papers published since 2006 on frustrated Lewis pair (FLP) chemistry the development of innovative Lewis acids and Lewis bases is a quickly expanding field. This thesis is separated into two parts. The first part investigates the incorporation of tridentate ligands on ruthenium alkylidene species and their subsequent reactivity with Lewis acids and FLPs in an attempt to synthesize innovative olefin metathesis catalysts. The second part explores the use of ligands coordinated to ruthenium metal centers as a method for expanding the Lewis acid and base functionalities in the field of FLP chemistry. Ruthenium-alkylidene complexes of the general formula ((PEP-Cy)RuX2(CHPh) (E = O, NH, NMe; X = Cl, Br)) were obtained via the reaction of Grubbs 1st generation catalysts with the tridentate ancillary ligands O(CH2CH2PCy2)2 [POP-Cy], HN(CH2CH2PCy2)2 [PN(H)P-Cy] and MeN(CH2CH2PCy2)2 [PN(Me)P-Cy]. Subsequent treatment of GaX3 with these alkylidene species resulted in the formation of cationic alkylidyne-hydride complexes, ([(PEP Cy)Ru(H)(X)(CPh)][GaX4] where E = O, NH, NMe; X = Cl, Br; however, when E = NH, a mixture of alkylidyne-hydride and cationic alkylidene species was observed. Conversely, when E = NMe, alkylidyne-hydride formation was followed by transfer of the alkylidene fragment to the Me of the ligand framework. Subsequently, Ru-acetylide complexes [LRu(PPh3)2CCPh] were reacted with the B(C6F5)3 to afford the para-attacked products [LRu(PPh3)2C=C(Ph)((C6F4)B(F)(C6F5)2)] (L = Cp, Indenyl). Further studies revealed that [IndRu(PPh3)2CCPh] and ER3 (E = B, R = C6F4H; E = Al, R = C6F5) formed FLP mixtures that effected the activation of CO2 between the nucleophilic β-acetylide carbon and the Lewis acid to form [IndRu(PPh3)2C=C(Ph)C(O)O-ER3] or [IndRu(PPh3)2C=C(Ph)C(O ER3)2] when E = Al and R = C6F5. Similarly, these FLP combinations were used to activate phenylacetylene and benzaldehyde forming the species [IndRu(PPh3)2C=C(Ph)C(Ph)=C(H)(ER3)] and [IndRu(PPh3)2C=C(Ph)C(Ph)O-ER3], respectively. Lastly, the synthesis of [((Ph2PC6H4)2BCl)(η6-Ph))RuCl] was achieved via the reaction of (Ph2PC6H4)2BPh with (Ph3P)RuCl2. Subsequent halide abstraction with K[B(C6F5)4] resulted in the formation of [((Ph2PC6H4)2B)(η6-Ph))RuCl][B(C6F5)4] which was used as a carbon-based Lewis acid in adduct formation with Lewis bases to yield products of the general form [((Ph2PC6H4)2B)(η5 C6H5 o-LB))RuCl][B(C6F5)4] (LB = PPh3, PCy3, PMe3, SIMes, etc). The activation of H2 was also achieved when combinations of [((Ph2PC6H4)2B)(η6-Ph))RuCl][B(C6F5)4] and bulky phosphines were employed, resulting in the products [((Ph2PC6H4)2B)(η5 C6H6))RuCl][B(C6F5)4], [((Ph2PC6H4)2B)(η6 C6H5))RuCl][B(C6F5)4] and [R3PH][B(C6F5)4] (R = Mes, tBu, Cy). Similarly, [((Ph2PC6H4)2B)(η6-Ph))RuCl][B(C6F5)4] was used to catalytically hydrogenate sterically encumbered aldimines at room temperature with catalyst loadings as low as 1 mol% via a FLP-type mechanism.

With hundreds of papers published since 2006 on frustrated Lewis pair (FLP) chemistry the development of innovative Lewis acids and Lewis bases is a quickly expanding field. This thesis is separated into two parts. The first part investigates the incorporation of tridentate ligands on ruthenium alkylidene species and their subsequent reactivity with Lewis acids and FLPs in an attempt to synthesize innovative olefin metathesis catalysts. The second part explores the use of ligands coordinated to ruthenium metal centers as a method for expanding the Lewis acid and base functionalities in the field of FLP chemistry. Ruthenium-alkylidene complexes of the general formula ((PEP-Cy)RuX2(CHPh) (E = O, NH, NMe; X = Cl, Br)) were obtained via the reaction of Grubbs 1st generation catalysts with the tridentate ancillary ligands O(CH2CH2PCy2)2 [POP-Cy], HN(CH2CH2PCy2)2 [PN(H)P-Cy] and MeN(CH2CH2PCy2)2 [PN(Me)P-Cy]. Subsequent treatment of GaX3 with these alkylidene species resulted in the formation of cationic alkylidyne-hydride complexes, ([(PEP Cy)Ru(H)(X)(CPh)][GaX4] where E = O, NH, NMe; X = Cl, Br; however, when E = NH, a mixture of alkylidyne-hydride and cationic alkylidene species was observed. Conversely, when E = NMe, alkylidyne-hydride formation was followed by transfer of the alkylidene fragment to the Me of the ligand framework. Subsequently, Ru-acetylide complexes [LRu(PPh3)2CCPh] were reacted with the B(C6F5)3 to afford the para-attacked products [LRu(PPh3)2C=C(Ph)((C6F4)B(F)(C6F5)2)] (L = Cp, Indenyl). Further studies revealed that [IndRu(PPh3)2CCPh] and ER3 (E = B, R = C6F4H; E = Al, R = C6F5) formed FLP mixtures that effected the activation of CO2 between the nucleophilic β-acetylide carbon and the Lewis acid to form [IndRu(PPh3)2C=C(Ph)C(O)O-ER3] or [IndRu(PPh3)2C=C(Ph)C(O ER3)2] when E = Al and R = C6F5. Similarly, these FLP combinations were used to activate phenylacetylene and benzaldehyde forming the species [IndRu(PPh3)2C=C(Ph)C(Ph)=C(H)(ER3)] and [IndRu(PPh3)2C=C(Ph)C(Ph)O-ER3], respectively. Lastly, the synthesis of [((Ph2PC6H4)2BCl)(η6-Ph))RuCl] was achieved via the reaction of (Ph2PC6H4)2BPh with (Ph3P)RuCl2. Subsequent halide abstraction with K[B(C6F5)4] resulted in the formation of [((Ph2PC6H4)2B)(η6-Ph))RuCl][B(C6F5)4] which was used as a carbon-based Lewis acid in adduct formation with Lewis bases to yield products of the general form [((Ph2PC6H4)2B)(η5 C6H5 o-LB))RuCl][B(C6F5)4] (LB = PPh3, PCy3, PMe3, SIMes, etc). The activation of H2 was also achieved when combinations of [((Ph2PC6H4)2B)(η6-Ph))RuCl][B(C6F5)4] and bulky phosphines were employed, resulting in the products [((Ph2PC6H4)2B)(η5 C6H6))RuCl][B(C6F5)4], [((Ph2PC6H4)2B)(η6 C6H5))RuCl][B(C6F5)4] and [R3PH][B(C6F5)4] (R = Mes, tBu, Cy). Similarly, [((Ph2PC6H4)2B)(η6-Ph))RuCl][B(C6F5)4] was used to catalytically hydrogenate sterically encumbered aldimines at room temperature with catalyst loadings as low as 1 mol% via a FLP-type mechanism.

The side-on dioxygen adducts of N-heterocyclic carbene (NHC) containing rhodium complexes, [ClRh(IPr)2(O2)] and [ClRh(IMes)2(O2)], previously synthesized in our laboratories possess a square planar geometry and O-O bond lengths of 1.323(3) and 1.341(4) Å, respectively. Both of these attributes are uncharacteristic of Rh(O2) complexes, which are typically octahedral and possess O-O bond lengths of approximately 1.45 Å. Full characterization by NMR, IR, Raman, DFT and XAS confirmed the short O-O bond lengths of these structures and revealed that they were rhodium(I) coordination complexes of singlet oxygen with no net oxidation/reduction process having taken place. The unique bonding mode appears to result from the interaction of a filled Rh d orbital with one of the two degenerate O2 * orbitals, which causes splitting of the O2 * orbitals, favoring spin pairing in the O2 HOMO, and the inability of Rh to donate electron density to the empty * orbital. Initial investigations of these complexes as catalysts for the reduction and oxidation of C-O bonds, as well as singlet oxygen generation were also undertaken. Rh(IPr)2 coordination complexes of N2, H2 and CO were also synthesized and characterized by X-ray crystallography, NMR and elemental analysis. Interestingly, the addition of hydrogen gas to rhodium did result in oxidation of the metal. A Rh(NHC) complex featuring an anionic acetate ligand, [(AcO)Rh(IPr)(CO)2], was synthesized and characterized by NMR, IR and X-ray crystallography. This complex proved to be an effective catalyst for the regioselective hydroformylation of aliphatic and aromatic alkenes, which occurred without isomerization of the alkene. Initial rates of hydroformylation with our catalyst were compared to the chloride analogue, [ClRh(IPr)(CO)2], and demonstrated the beneficial nature of replacing the halide with a carboxylate ligand, which is less inhibiting of the reaction. The synthesis of a bifunctional hydrogenation catalyst featuring a protic-NHC was attempted by addition of benzimidazoles to [Cl2Ru(diphosphine)]. Although these attempts were unsuccessful, a large number of complexes of the formula [Cl2Ru(diphosphine)(-N3-benzimidazole)2] were synthesized and proved to be effective catalysts for the chemoselective hydrogenation of ketones versus alkenes. Use of chiral diphosphines and 1-triphenylmethylbenzimidazole yielded catalysts capable of producing secondary alcohols with moderate enantioselectivity. / Thesis (Ph.D, Chemistry) -- Queen's University, 2010-09-17 12:44:52.686

In the last decade N-heterocyclic carbene (NHC) ligands have become important in organometallic chemistry and homogeneous catalysis, rivalling the well established phosphines. Most of the current attention to date has focused on the NHC complexes of the platinum group metals (rhodium, palladium and nickel) plus ruthenium based system, but the chemistry of NHC systems of iron which is relatively inexpensive and environmentally friendlier is considerably less developed. Thus, this project involves the design, synthesis, characterization and application in catalytic transfer hydrogenation of NHC ligands and their iron(II) complexes. The motivation for the choice of NHC as a ligand stems from the ability to systematically tune the ligand both electronically and sterically in addition to the stability and robustness of the ligand to stabilize metal centres in various environments. In this research imidazolium based NHCs are generated. Thus, three different series of imidazolium salts were synthesized and their iron(II) complexes was obtained. All the compounds were characterized by spectroscopic and crystallographic methods. These are: (a) 1,3-dialkylimidazolium salts (b) 1,3-diarylimidazolium salts and (c) ferrocenylimidazolium salts bearing methyl and phenyl spacers between the ferrocenyl and the imidazolium moieties. A total of 20 novel compounds were synthesized and are reported in this thesis. Furthermore, the application of the new compounds as transfer hydrogenation catalysts was investigated using 17 saturated and unsaturated ketones as substrates, in the presence of KOH as the base and 2-propanol as the hydrogen source. The dialkylated NHC iron(II) complexes showed excellent yields, and TON values of up to 200 were achieved under the optimized reaction conditions. Without complexation with iron, the 1,3-diarylimidazolium and ferrocenylimidazolium series of salts were also found to be active catalysts for the transfer hydrogenation reaction of ketones in alcoholic media. In the case of ferrocenylimidazolium salts a TON value up to 1880 was achieved. Notably, two of the unsaturated ketones were successfully converted at a high yield with a high selectivity to the corresponding saturated ketones only. In addition, the stability of NHC ligands to moisture was investigated, since an understanding of the stability of various deprotonated NHC-based imidazolium cations to attack by moisture resulting in hydrolysis products is very important to understanding the coordination chemistry of the ligands on to metal centres. Four novel ionic diamino aldehyde compounds were obtained by moisture attack on saturated NHC ligands. The route to the formation of the hydrolysed compounds is formulated to occur via an imidazolinium ring opening process. On the other hand the unsaturated counterparts were more stable towards hydrolysis yielding adducts with the iron(II) precursors. Finally, the electrochemical properties of the ferrocenylimidazolium salts were investigated using cyclic voltametry. By comparing the relative shifts in the formal electrode potentials of the ferrocene/ferrocenium coupled with the ferrocenylimidazolium salts, it was easy to evaluate the influence of the substituents on the carbene containing imidazolium moiety on the electrochemical properties of the iron centres. The formal electrode potential of the ferrocenylimidazolium salts shifted to higher positive potentials as compared to ferrocene, indicating a high electron withdrawing effect of the imidazolium salts. This makes the metal centres more vulnerable to attack by nucleophiles. The electrochemical studies have enabled a structure-activity correlation to be drawn for the various ferrocenylimidazolium salts. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2011.