This thesis discusses reduction and oxidation reactions catalysed by the perrhenate anion and oxidation reactions catalysed by other oxo-anions i.e. sulfate and nitrate. Chapter one introduces catalytic hydrosilylation, hydroboration, deoxydehydration and alkene epoxidation and some of their applications, with a focus on high oxidation state complexes. Chapter two describes the synthesis of a salt of perrhenate [N(hexyl)4][ReO4] which is highly soluble in organic solvents. The use of this salt as a catalyst for both the hydrosilylation and hydroboration of carbonyl compounds and carbon dioxide is discussed. Catalytic methylation of amines and anilines with carbon dioxide and hydrosilanes is also reported. Labelled carbon dioxide reactions and DFT calculations are conducted in order to understand the mechanism of carbon dioxide reduction using hydrosilanes. Chapter three outlines the synthesis of a number of alkylammonium and pyridinium perrhenate salts and their application in the deoxydehydration reaction, converting vicinal diols to alkenes. The role of the counterion is discussed with pyridinium perrhenates shown to be more effective catalysts. DFT calculations are conducted to identify the most likely pathway of the catalytic cycle. Alternative reducing agents to the triphenylphosphine initially used are also studied. Chapter four reports results of organic salts of perrhenate, sulfate and nitrate as oxidation catalysts, specifically their ability to catalyse epoxidations of alkenes. By the formation of supramolecular ion pairs (SIPs), these anions are made organic soluble which is found to significantly enhance their catalytic ability, however, the organic counterions used to form these SIPs were found to be of importance. Ionic liquids are also used for the epoxidation of alkenes. Solution studies are presented to further understanding of how these compounds interact with one another in solution. Chapter five contains experimental conditions and characterisation for compounds discussed in this work.