Silsesquioxane Chemistry, 4.: Silsesquioxane Complexes of Titanium(III) and Titanium(IV)

Reaction of the incompletely condensed silsesquioxane derivative Cy7Si7O9(OH)3 (1) with Ti(OEt)4 affords the dimeric titanasilsesquioxane [(Cy7Si7O12)Ti(μ-OEt)(EtOH)]2 (13) in 81% yield. The known titanasilsesquioxane [Cy7Si7O11(OSiMe3)]2Ti (18) has been prepared through a modified procedure starting from titanium tetraalkoxides. Novel oxotitanium silsesquioxane derivatives are obtained from reactions of titanocene dihalides with Cy7Si7O9(OH)2(OSiMe3) (14). Cp2TiCl2 yields dinuclear (μ-O)[{Cy7Si7O11(OSiMe3)}TiCp]2 (19), while with Cp*2TiCl2 the trinuclear titanacycle Cp*2Ti3O3[Cy7Si7O11(OSiMe3)]2 (20) is obtained. In addition, a new synthetic route to model compounds for titanium catalysts immobilized on silica has been developed. Disilylated Cy7Si7O9(OH)(OSiMe3)2 (15) cleanly reacts with the ‘tucked-in’ fulvene complex Cp*Ti(C5Me4CH2) to give the titanium(III) silsesquioxane Cp*2Ti[Cy7Si7O10(OSiMe3)2] (21). In a similar manner treatment of Cp*Ti(C5Me4CH2) with Cy7Si7O9(OH)2(OSiMe3) (14) affords the mono(pentamethylcyclopentadienyl) complex Cp*Ti[Cy7Si7O11(OSiMe3)][Cy7Si7O10-(OH)(OSiMe3)] (22) which is an advanced model compound for a catalytically active titanium center on a silica surface. The molecular structures of these titanium silsesquioxane derivatives have been determined by X-ray diffraction analyses.