CATALYTIC ELECTROCHEMICAL SYNTHESIS USING NANOCRYSTALLINE TITANIUM-DIOXIDE CATHODES IN MICROEMULSIONS

Compared to similar catalysts dissolved in solution, electrolysis usin g a cobalt complex chemisorbed onto nanocrystalline titanium dioxide c athodes was catalytically more efficient in a microemulsion for the de bromination of dibromocyclohexane, and the stereoselective cyclization of 2-(4-bromobutyl)-2-cylohexen-1-one to 1-decalone. 1,2-Dibromocyclo hexane was converted to cyclohexene with 100 h(-1) turnover using TiO2 electrodes coated with vitamin B-12 hexacarboxylate. This represented a 5-fold increase in the turnover number compared to the same reactio n catalyzed using vitamin Bla in solution on a bare carbon electrode. Cyclization of 2-(4-bromobutyl)-2-cyclohexen-1-one in the microemulsio n gave similar trans:cis ratios (14-18) for product 1-decalone for bot h soluble-and adsorbed catalyst systems, but more than 100-fold larger turnover number using the coated TiO2 electrodes. In DMF, the coated TiO2 gives little stereoselectivity for this reaction, and poorer turn over than that in the microemulsion. Binding vitamin B-12 hexacarboxyl ate onto TiO2 electrodes improves electron-transfer rates and catalyti c efficiency while retaining essential features of cobalt complex-medi ated catalysis in microemulsions.