Reactivity of titanium oxo ethoxo cluster [Ti16O16(OEt)32]. Versatile Precursor of Nanobuilding Block-Based Hybrid Materials reactions.
Résumé
Oxo alcoxo metallic clusters can be employed as inorganic nanobuilding blocks to obtain welldefined organic-inorganic hybrid materials. A better understanding of the surface reactivity of the clusters should allow optimization of the elaboration of hybrid materials through a better control of the hybrid interface. The oxo alcoxo cluster Ti16O16(OEt)32 presents a shell of labile ethoxy groups that can be selectively transalcoholyzed with preservation of the titanium oxo core, leading to new oxo alcoxo clusters Ti16O16(OEt)32-x(OR)x (R: alkyl, phenyl, styrenic, etc. groups). The reactivity of the Ti16O16(OEt)32 cluster toward aliphatic and aromatic alcohols is investigated to determine both the kinetics and the number of substituted titanium atoms, which are strongly dependent on the nature of the alcohol. Characterization of the organic modification of the cluster is performed in situ by liquid 13C NMR measurements, using the molecular structures of two new clusters, Ti16O16(OEt)28(OnPr)4 and Ti16O16(OEt)24(OnPr)8 (OnPr ) propoxy groups), as references. The structures of these clusters have been established using single-crystal X-ray diffraction. Moreover, a complete spectroscopic assignment of each ethoxy group is proposed after combining crystallographic data, 13C NMR T1 relaxation measurements, and 1H-1H, 1H-13C 2D NMR experiments. Finally, the cluster is functionalized with polymerizable ligands via transalcoholysis and transesterification reactions using hydroxystyrene and acetoxystyrene.