Catalytic Electrochemical Synthesis Using Nanocrystalline Titanium Dioxide Cathodes in Microemulsions

Compared to similar catalysts dissolved in solution, electrolysis using a cobalt complex chemisorbed onto nanocrystalline titanium dioxide cathodes was catalytically more efficient in a microemulsion for the debromination of dibromocyclohexane, and the stereoselective cyclization of 2-(4-bromobutyl)-2-cylohexen-1-one to 1-decalone. 1,2-Dibromocyclohexane was converted to cyclohexene with 100 h - 1 turnover using TiO 2 electrodes coated with vitamin B 12 hexacarboxylate. This represented a 5-fold increase in the turnover number compared to the same reaction catalyzed using vitamin B 12 in solution on a bare carbon electrode. Cyclization of 2-(4-bromobutyl)-2-cyclohexen-1-one in the microemulsion gave similar trans: cis ratios (14−18) for product 1-decalone for both soluble and adsorbed catalyst systems, but more than 100-fold larger turnover number using the coated TiO 2 electrodes. In DMF, the coated TiO 2 gives little stereoselectivity for this reaction, and poorer turnover than that in the microemulsion. Binding vitamin B 12 hexacarboxylate onto TiO 2 electrodes improves electron-transfer rates and catalytic efficiency while retaining essential features of cobalt complex-mediated catalysis in microemulsions.