Ethylene polymerization with dimeric zirconium and hafnium silsesquioxane complexes

Treatment of the silanol (c-C5H9)(7)Si8O12(OH) with Cp " Ti(CH2Ph)(3) (Cp " = 1,3-C5H3(SiMe3)(2)) or TiCl4 selectively affords the mono(silsesquioxane) complexes Cp "[(c-C5H9)7Sis0l3ITi(CH2Ph)(2) (1) and [(c-C5H9)(7)Si8O13]TiCl3 (2), respectively, while with M(CH2Ph)(4) (M = Ti, Zr, Hf) mixtures of products were obtained. When the disilanol (c-C5H9)(7)Si7O9(OSiMe3)(OH)(2) is reacted with M(CH2Ph)(4) (M = Ti, Zr), the bis(silsesquioxane) complexes [(c-C5H9)(7)Si7O11(OSiMe3)](2)M (M = Ti (3), Zr (4), Zr . 2THF (5)) are formed exclusively. With (PhCH2)(2)ZrCl2. OEt2 as precursor, the mono(silsesquioxane) complex [(c-C5H9)(7)Si7O11(OSiMe3)]ZrCl2. 2THF (6) can be isolated. M(CH2Ph)(4) (M = Ti, Zr, Hf) reacts smoothly with the tris(silanol)(c-C5H9)(7)Si7O9(OH)3 (III), giving the metallasilsesquioxane benzyl species, {[(c-C5H9)(7)Si7O12]MCH2Ph}(n) (M = Ti, n = 1(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 alpha-olefin hydrogenation catalysts. Without cocatalyst, the neutral dimers 8 and 9 are poor, though active ethylene polymerization catalysts (activity: (5-10) x 10(3) g PE/mol.h)). Addition of B(C6F5)(3) affords the cationic, mono(benzyl) complexes {[(c-C5H9)(7)Si7O12](2)M-2(CH2Ph)}((+)) (M = Zr, Hf): single-site catalysts(activity: (2-8) x 10(6) 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 g form bis(THF) adducts, [(c-C5H9)(7)Si7O11(OSiMe3)](2)Zr . 2THF (5) and [(c-C5H9)(7)Si7O12]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.