Synthesis and Reactivity of Core-Functionalized Polyhedral Titanasiloxanes

Condensation reactions of cyclopentadienyl silanetriols with titanium alkoxides yield oligomeric titanasiloxanes in high yields. Two types of polyhedral structures can be obtained by small structural modifications at the reactants (Cp^RSi(OH)<INF>3</INF>, Ti(OR)<INF>4</INF>) or by variation of reaction parameters. Thus, reaction of the silanetriols 9-(Me<INF>3</INF>Si)Fluorenyl-Si(OH)<INF>3</INF> (<BO>1</BO>) and Cp*Si(OH)<INF>3</INF> (<BO>2</BO>) with Ti(O^tBu)<INF>4</INF> leads to the cubic Ti<INF>4</INF>O<INF>12</INF>Si<INF>4</INF> polyhedrons [9-(Me<INF>3</INF>Si)Fluorenyl-Si]<INF>4</INF>O<INF>12</INF>[TiO^tBu]<INF>4</INF> (<BO>3</BO>) and [Cp*Si]<INF>4</INF>O<INF>12</INF>[TiO^tBu]<INF>4</INF> (<BO>4</BO>), respectively, while co-condensations of <BO>1 </BO>with Ti(OⁱPr)<INF>4</INF> afford either the polyhedral titanasiloxane [9-(Me<INF>3</INF>Si)Fluorenyl-Si]<INF>4</INF>O<INF>12</INF>[TiOⁱPr]<INF>6</INF>[μ<INF>2</INF>-ⁱPrO]<INF>2</INF>[μ<INF>3</INF>-O]<INF>2</INF> (<BO>6</BO>) or the cubic polyhedron [9-(Me<INF>3</INF>Si)Fluorenyl-Si]<INF>4</INF>O<INF>12</INF>[TiOⁱPr]<INF>4</INF> (<BO>5</BO>), depending on the choice of temperature and solvent. Substitution reactions with Ph<INF>3</INF>SiOH, Me<INF>2</INF>NOH, or acetylacetone at the titanium centers proceed selectively under conservation of the respective TiOSi core structures, whereas substitution reactions at the silicon centers performed with ethanol, HCl, and water are connected with core degradation. Both the novel titanasiloxanes and their titanium-functionalized derivatives have been characterized by IR and NMR spectroscopy as well as by single-crystal X-ray diffraction studies. Thermolysis of <BO>3</BO> leads to quantitative formation of 9-(Me<INF>3</INF>Si)Fluorene and 2-methylpropene.