Modification of Mesoporous TiO2Electrodes with Cross-Linkable B12Derivatives

The modification of mesoporous TiO2 film electrodes with vitamin B12 derivatives (e.g., 1, 2, or 3) yields electrodes with interesting sensing and electrocatalytic properties. So far, only coordinative bonding between the B12 derivatives and the metal oxide surface was used, and B12 was lost under conditions of extended electrocatalysis [1. Schulthess, P.; Ammann, D.; Simon, W.; Caderas, C.; Stepanek, R.; Krautler, B. Helv. Chim. Acta 1984, 67 (4), 1026−1032. 2. Mayor, M.; Scheffold, R.; Walder, L. Helv. Chim. Acta 1997, 80 (4), 1183−1189. 3. Stepanek, R. Ph.D.; ETH: Zürich, 1987].1-3 We report here on a procedure that yields highly improved stabilities of the electrocatalysts toward reductive expulsion from the mesopores. It is based on cross-linking the B12 derivatives (4 or 5) equipped with multiple reaction sites in the TiO2 mesopores. The cross-linkers are multiple functionalized, one of them assisting the electron transfer from TiO2 to the Co centers via redox shuttling. The modified electrodes show high electrocatalytic reactivity toward organic halides and highly improved stability.