Monomeric peroxo titanate coordinated with cyclohexanediaminetetraacetate: Towards the active oxygen species of the Ti(IV) site hosted in the titanium silicalite catalyst TS-1

Hexadentate chelated trans-1,2-cyclohexanediaminetetraacetato titanate(IV) was used as a model of the Ti(IV) species in the constrained environment of TS-1 (H4cdta = trans-1,2-cyclohexanediaminetetraacetic acid, C14H22O8N2; TS, titanium silicalite). Several complexes were isolated and well characterized, including [Ti(cdta)(H2O)]·2H2O (1), Na2[Ti(O2)(cdta)]·2H2O (2) and (NH4)2[TiO(cdta)]·1.5H2O (3). Octadentate cdta peroxo titanate(IV) (2) is obtained quantitatively from the reaction of the hydrated titanium cdta complex 1 with hydrogen peroxide. The bond distances between O–O and Ti–(O2) are 1.464(3) and 1.908(2) Å, respectively. Transformation of the peroxo titanium(IV) complex with excess H4cdta and heating results in the formation of an interesting oxotitanate in H2O–H2O2 solution. The catalytic activity of 2 was studied for phenol hydroxylation using 30% H2O2, and this was monitored by 1H and 13C NMR techniques. The main product of the reaction is catechol.

Aquo-titanium cyclohexanediaminetetraacetate dihydrate [Ti(cdta)(H2O)]·2H2O was converted to its peroxo species quantitatively. Excess cdta ligand and heating results in the formation of the ammonium cdta oxotitanate (NH4)2[TiO(cdta)]·1.5H2O. The catalytic activity of peroxo titanate Na2[Ti(O2)(cdta)]·2H2O was tested for phenol hydroxylation using hydrogen peroxide. The main product of the reaction is catechol. The peroxo catalytic species is used as a model for the titanium silicalite catalyst TS-1.Figure optionsDownload as PowerPoint slideHighlights
► Aquo-titanium cyclohexanediaminetetraacetate was converted to peroxo species quantitatively.
► Excess cdta ligand and heating result in the formation of cdta oxotitanate.
► Its catalytic activity of peroxo cdta titanate was tested for phenol hydroxylation.