| Methodology, discovered and refined by parallel screening, is described for the epoxidation of alkenes. It uses hydrogen peroxide as the terminal oxidant, is promoted by catalytic amounts (1.0–0.1 mol %) of manganese (2+) salts, and must be performed using at least catalytic amounts of bicarbonate buffer. Peroxymonocarbonate, HCO4− , forms in the reaction, but without manganese, minimal epoxidation is observed in the solvents used in this research, which is DMF and tBuOH. More than 30 d-block and f-block transition metal salts were screened for epoxidation activity under similar conditions, but the best catalyst found was MnSO4. EPR studies show that Mn 2+ is initially consumed in the catalytic reaction, but is regenerated towards the end of the process presumably when the hydrogen peroxide is spent. A variety of aryl-substituted, cyclic, and trialkyl-substituted alkenes were epoxidized under these conditions using ten equivalents of hydrogen peroxide, but monoalkyl-alkenes were unreactive.; To improve the substrate scope, and to increase the efficiency of hydrogen peroxide consumption, 68 diverse compounds were screened to find additives that would enhance the rate of the epoxidation reaction relative to competing disproportionation of hydrogen peroxide. Successful additives were 6 mol % sodium acetate in the tBuOH system, and 4 mol % salicylic acid in the DMF system. These additives enhanced the rate of the desired epoxidation reaction by 2–3 times. Reactions performed in the presence of these additives require less hydrogen peroxide, shorter reaction times, and enhance the yields obtained from less reactive alkene substrates. Possible mechanisms for the reaction are discussed.; Bis-imidazolium ligand precursors were designed and synthesized for the formation of iron or manganese bis-carbene asymmetric epoxidation catalysts. The ligands were synthesized in a concise manner to yield pure products upon tritaration with diethyl ether. Several different routes were tried to form the corresponding catalysts with little success. Reasons for the failure of these ligand precursors to form organometallic complexes are discussed in addition to other possible uses of these ligands. |
