Molybdenum plays an essential role in the biological activity of the metalloenzyme nitrogenase, which is responsible for the initial stages of nitrogen fixation. Although the metal containing site of this enzyme has been demonstrated to consist of an unusual Mo-Fe-S cluster, FeMo-co, synthetic representations based upon Mo/Fe/S systems have failed to exhibit the substrate binding or reducing properties of the enzyme. In fact, despite intense activity in the field of molybdenum-sulfur chemistry, examples of species possessing a molybdenum-sulfur core capable of incorporating small molecules such as acetylenes, carbon monoxide, hydrazines or dinitrogen are extremely rare. The propensity of simple thiolate ligands to act as bridging groups and the tendency of molybdenum species to form oxo-bridged dimers are both likely to be incompatible with the objective of isolating species with the (Mo(SR)n)-core, capable of binding small molecules. These problems may be overcome by using sterically-hindered thiolate ligands which stabilize formally coordinatively unsaturated complexes of molybdenum in lower oxidation states, such as Mo(II) and Mo(IV). In addition, multidentate thiolate ligands may be designed so as to provide protective cavities to enclose a substrate molecule. The objectives of the research are to synthesize novel sterically-hindered thiolate ligands; to prepare complexes of the general class (Mo(SR)n)m-with both monodate and multidentate sterically-hindered demanding thiolate ligands; to characterize these species structurally and spectroscopically; to investigate the incorporation of small molecules such as carbon monoxide, nitric oxide, hydrazines, acetylenes, and dinitrogen; and to initiate electrochemical studies of organo-sulfur complexes of molybdenum in lower oxidation states in order to establish general redox trends and to produce potentially more reactive intermediates.
