Surface-Induced Deprotection of THP-Protected Hydroxamic Acids on Titanium Dioxide

Hydroxamic acids chelate metals with high affinity and form hydrolytically stable complexes with metal oxides such as TiO₂. However, these appealing binding properties can cause problems during the preparation and application of metallocatalysts with appended hydroxamate anchoring groups. Here we show that the tetrahydropyran (THP) O-protected hydroxamate group can be cleaved in situ on a TiO₂ surface at room temperature, leading to the surface-bound species. Surface-mediated deprotection has several advantages over direct surface functionalization including increased hydrolytic stability of the covalent interaction with the metal oxide surface and decreased aggregation of the surface species. Application of the surface-mediated chelation method for dye-sensitized photoelectrochemical cells (DSPC) was examined using the organic dye MK-2. Results show that the surface-mediated deprotection led to improved DSPC performance attributed to a decrease in dye aggregation relative to a DSPC prepared using standard methods. This simplified approach using THP-protected hydroxamates provides a convenient new method for functionalizing metal oxides.