The study involves synthetic approaches towards the preparation of novel NHC complexes of low valent rhenium and manganese transition metals. Diverse methods of synthesis were studied. The direct approach, in which the ylidene obtained from deprotonation of 1,3-bis(2,4,6- trimethylphenyl)imidazolium chloride was added to the metal substrate, proved to be unsuccessful as isolation of the free carbene should rather be performed in an argon filled glove box under extreme inert conditions. By way of further investigation the ylidene was prepared by in situ methods and then quenched with the metal substrate. Different bases for deprotonation purposes and reaction conditions were explored. All routes employed were investigated and compared using group VII transition metal substrates Re(CO)5Br, Mn(CO)5Br, Re2(CO)10 and Mn2(CO)10. Isolation and purification of these products proved to be very challenging due to the insolubility in some organic solvents with consequent problematic spectroscopic analyses of the complexes. The tendency of the products to undergo various side reactions is observed in all reactions. Specifically, hydrolysis of the imidazolium ligand, followed by vinyl formation, yielded the mesitylformamide compound (3). The results obtained for some of the monometal substrates indicated that the target complexes were formed but could not be isolated. However, the synthesis route employing deprotonation by nBuLi as base and [Mn2(CO)10] as dimetal substrate lead to the isolation of the target dinuclear complex [Mn2(CO)9IMes] (9). Other novel complexes obtained during the course of this study include the biscarbene tetrarhenium complex [Re2(CO)9.C(OEt)C4H2OC(OEt)Re2(CO)9] (12) and various side reaction products. In many cases, metal-metal bond cleavage and carbonyl insertion was observed, as is evident in the complex IMesH[ReO4] (6) and ketene product (13). Structural and theoretical studies were performed to investigate the bond character between the carbene ligand and the metal. / Dissertation (MSc)--University of Pretoria, 2010. / Chemistry / unrestricted

Chelation of first-row transition metals has many useful properties in the biomedical and industrial fields due to the stabilizing and/or property-altering effects that certain chelates can induce in these metals. One such useful design principle for these chelates is the addition of bulky steric groups which can have an added effect on these properties. Chapter I will explore the origins of these effects and show examples of how these effects are leveraged to produce useful complexes in a variety of applications. In Chapter II, we will discuss our choice of ligand design and the development of related synthetic procedures for all organic portions of the complexes. In Chapter III, we then study the effects of the series of bulky ligands with Mn2+ and Zn2+ on the formation of thermodynamically and kinetically inert complexes and investigate the subsequent effects on redox properties. Chapter IV furthers this investigation with Fe2+ and Co2+ using the bulkiest and least bulky versions of our ligand, where these metal complexes are investigated for the effects on redox properties and spin states. Lastly, a brief appendix details work performed on pyridine-imidazole systems bound to Mn2+ for their potential use in water oxidation catalysis.