Polyoxotitanates join the Keggin family: Synthesis, structure and reactivity of [Ti18O28H][OBu(t)](17)

Reaction of Ti(OBu(t))(4) with about 1 equivalent of water in tert-butyl alcohol for 5 d at 100 degrees C yielded the polytitanate complex [Ti18O28H][OBu(t)](17). A single-crystal X-ray diffraction study of its Bu(1)OH solvate [a = 15.789(4), b = 29.544(5), c = 27.496(5) Angstrom, beta = 91.85(5)degrees; Z = 4; space group P2(1)/c-C-2h(5)] revealed a Ti18O45 metal-oxygen framework having a pentacapped Keggin structure, i.e. a Ti13O40 Keggin unit capped by five TiO moieties which lie above five of the six approximately square faces of the T-d-distorted cuboctahedron defined by the metals in the Keggin unit. All seventeen of the terminal oxygen atoms are bonded to tert-butyl groups. This complex is the most highly condensed titanium alkoxide hydrolysis product isolated to date and showed good stability in solution, retaining its structure and showing no decomposition after 24 h at ambient temperature in toluene-tert-butyl alcohol solution, according to NMR spectroscopy. Reactions of the complex with water, 2-methylbutan-2-ol and triethylamine are also reported.