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• 17520-19-3 tetrabenzyl titanium 
• 183387-28-2 1,3,5,7,9,11,14-heptacyclopentyltricyclo[7.3.3.15,11]heptasiloxane-endo-3,7,14-triol 

Relevant academic research and scientific papers

Ethylene polymerization with dimeric zirconium and hafnium silsesquioxane complexes

Treatment of the silanol (c-C5H9)7Si8O12(OH) with Cp″Ti(CH2Ph)3 (Cp″ = 1,3-C5H3(SiMe3)2) or TiCl4 selectively affords the mono(silsesquioxane) complexes Cp″[(c-C5H9)7Si8O 13]Ti(CH2Ph)2 (1) and [(c-C5H9)7Si8O 13]TiCl3 (2), respectively, while with M(CH2Ph)4 (M = Ti, Zr, Hf) mixtures of products were obtained. When the disilanol (c-C5H9)7Si7O9(OSiMe 3)(OH)2 is reacted with M(CH2Ph)4 (M = Ti, Zr), the bis(silsesquioxane) complexes [(c-C5H9)7Si7O 11(OSiMe3)]2M (M = Ti (3), Zr (4), Zr-2THF (5)) are formed exclusively. With (PhCH2)2ZrCl2OEt2 as precursor, the mono(silsesquioxane) complex [(c-C5H9)7Si7On(OSiMe 3)]ZrCl2·2THF (6) can be isolated. M(CH2Ph)4 (M = Ti, Zr, Hf) reacts smoothly with the tris(silanol) (c-C5H9)7Si7O9(OH) 3 (III), giving the metallasilsesquioxane benzyl species, {[(c-C5H9)7Si7O 12]MCH2Ph}n (M = Ti, n = l (7); M = Zr, n = 2 (8); M = Hf, n = 2 (9)). Compounds 5 and 8 have been characterized by X-ray analysis. Dimer 8 consists of a zwitterionic-like structure with two electronically different metal sites. M - C bond hydrogenolysis of 8 and 9 affords the corresponding hydrides, which are active α-olefin hydrogenation catalysts. Without cocatalyst, the neutral dimers 8 and 9 are poor, though active ethylene polymerization catalysts (activity: (5 - 10) × 103 g PE/(mol·h)). Addition of B(C6F5)3 affords the cationic, mono(benzyl) complexes {[(c-C5H9)7Si7O12] 2M2(CH2Ph)}(+) (M = Zr, Hf): single-site catalysts (activity: (2 8) × 106 g PE/(mol · h)) that are considerably more active than the neutral 8 and 9. Whereas titanasilsesquioxanes 3 and 7 do not react with THF, the corresponding zirconasilsesquioxanes 4 and 8 form bis(THF) adducts, [(c-C5H9)7Si7O 11(OSiMe3)]2Zr · 2THF (5) and [(c-C5H9)7Si7O 12]ZrCH2Ph · 2THF (10), which suggests that the titanium complexes are less electrophilic than the zirconium ones. Accordingly, the titanium complex 7 does not react with dihydrogen and is inactive in ethylene polymerization.

Synthesis and characterisation of titanium silasesquioxane complexes: Soluble models for the active site in titanium silicate epoxidation catalysts

Titanium silasesquioxane complexes have been prepared as models for the catalytically active centres in titanium silicate oxidation catalysts. Complexes [TiL(R7Si7O12)] [R = c-C6H11, L = CH2Ph 5, NMe2 6, OSiMe3 7, OPri 8 or OBut 9; R = c-C5H9, L = CH2Ph 13 or OPri14] were prepared from the reactions of incompletely condensed silasesquioxanes R7Si7O9(OH)3 1, 2 with homoleptic complexes TiL4. Aryloxy derivatives [TiL(R7Si7O12)] [R = c-C6H11, L = OPh 10, O-C6H4F-p 11 or O-C6H4NO2-p 12] were prepared from the reaction of 8 with the corresponding aryl alcohols. The 29Si and 13C NMR spectroscopic data obtained on 5-14 indicate that the local C3v symmetry of the silasesquioxane ligand is retained at titanium, consistent with the formation of monomeric complexes possessing tripodal geometry. The monomeric nature of 7 was confirmed by X-ray crystallography. For complexes 8-12 solution NMR spectroscopy reveals the presence of a dimer, containing μ-alkoxy ligands, in equilibrium with the monomer. The zirconium analogue of 9, [Zr(OBut){(c-C6H11)7Si 7O12}] 15, was similarly isolated as a monomer-dimer mixture from the reaction of the incompletely condensed silasesquioxane (c-C6H11)7Si7O9(OH) 3 with [Zr(OBut)4]. Reaction of the disilanol (c-C6H11)7Si7O 9(OSiMe3)(OH)2 4 with an excess of [Ti(OPri)4] afforded [Ti(OPri)2{(c-C6H11) 7Si7O11(OSiMe3)}] 16, containing a bidentate silasesquioxane ligand, while reactions with TiL4 (L = CH2Ph, NMe2 or OSiMe3) afforded [Ti{(c-C6H11)7Si7O 11(OSiMe3)}2] 17, independent of the stoichiometry of the reactants. Complexes 5-14 serve as soluble models for putative tripodal (open lattice) sites in titanium silicates, while 16 and 17 represent models for bipodal and tetrapodal (closed lattice) sites, respectively. From a study of the catalytic properties of complexes 5-17 in the epoxidation of oct-1-ene with tert-BuOOH (TBHP), revealing high activity for 5-14 and low activity for 16 and 17, it is concluded that the most active site in titanium silicate epoxidation catalysts corresponds to a four-co-ordinate site possessing tripodal geometry. Studies using IR and NMR spectroscopy show that, in the absence of olefins, putative alkylperoxo complexes formed by the addition of TBHP to tripodal complexes decompose rapidly at ambient temperature. Based on the high TBHP-to-epoxide selectivities observed under epoxidising conditions, it is apparent that the rate of epoxidation is significantly greater than that of alkylperoxo intermediate decomposition. The Royal Society of Chemistry 1999.