Turning over on sticky balls: preparation and catalytic studies of surface-functionalized TiO 2 nanoparticles.

We have investigated the reactivity of rhodium(iii) complex-functionalized TiO 2 nanoparticles and demonstrate a proof-of-principle study of their catalytic activity in an alcohol oxidation carried out under aqueous conditions water in air. TiO 2 nanoparticles (NPs) have been treated with (4-([2,2':6',2''-terpyridin]-4'-yl)phenyl)phosphonic acid, 1, to give the functionalized NPs (1)@TiO 2 . Reaction between (1)@TiO 2 NPs and either RhCl 3 ·3H 2 O or [Rh 2 (μ-OAc) 4 (H 2 O) 2 ] produced the rhodium(iii) complex-functionalized NPs Rh(1) 2 @TiO 2 . The functionalized NPs were characterized using thermogravimetric analysis (TGA), matrix-assisted laser desorption ionization (MALDI) mass spectrometry, 1 H NMR and FT-IR spectroscopies; the single crystal structures of [Rh(1) 2 ][NO 3 ] 3 ·1.25[H 3 O][NO 3 ]·2.75H 2 O and of a phosphonate ester derivative were determined. 1 H NMR spectroscopy was used to follow the reaction kinetics and to assess the recyclability of the NP-supported catalyst. The catalytic activity of the Rh(1) 2 @TiO 2 NPs was compared to that of a homogeneous system containing [Rh(1) 2 ] 3+ , confirming that no catalytic activity was lost upon surface-binding. Rh(1) 2 @TiO 2 NPs were able to withstand reaction temperatures of up to 100 °C for 24 days without degradation.