Cyclopentadienyl-hydrazido titanium complexes: Synthesis, structure, reactivity, and catalytic properties

Abstract

An eta(1)-hydrazido bis(dimethylamido) complex, [(eta(5)-C5Me4)SiMe2(eta(1)-NNMe2)]Ti(NMe2)(2) (2), has been prepared from a neat reaction of (C5Me4H)SiMe2(NHNMe2) (1) with Ti(NMe2)(4) at 130 degrees C via amine elimination. Treatment of 2 with Me3SiCl gives an eta(2)-hydrazido dichloro compound, [(eta(5)-C5Me4)SiMe2(eta 2-NNMe2)]TiCl2 (3). The reaction of 2 with excess AlMe3 (ca. 5 equiv) affords an AlMe3 adduct, [(eta(5)-C5Me4)SiMe2(eta(1)-NNMe2AlMe3)]TiMe2 (4), which is converted to a dimethyl complex, [(eta(5)-C5Me4)SiMe2(eta(2)-NNMe2)]TiMe2 (5), upon treatment with NEt3. The reaction of 5 with B(C6F5)(3) affords a methyl-triarylborate complex, [(eta(5)-C-5-Me-4)SiMe2(NNMe2)]TiM(mu-Me)B(C6F5)(3) (6). The reaction of 2 with H2O produces a tetrameric organotitanoxane [(eta(5)-C5Me4)(SiMe2NHNMe2)Ti](4)O-6 (7) with an adamantane-like cage structure. However, the reaction of 2 with H2O in the presence of HCl affords a dimeric complex [mu-(OSiMe2-eta(5)-C5Me4)TiCl2](2) (8). Compounds 1-8 have been characterized by spectroscopic and analytical data. Molecular structures of 2, 3, 4, 5, 7, and 8 have been determined by single-crystal X-ray diffraction studies. Complexes 2-5 contain eta(1)-hydrazido (2 and 4) and eta(2)-hydrazido (3 and 5) groups depending on the electronic nature of the titanium center. Reversible interconversion between eta(1)- and eta(2)-hydrazido moieties has been observed upon addition of either NEt3 (4 --> 5) or AlMe3 (5 --> 4). Complexes 2-5 exhibit moderate catalytic activities for the polymerization of ethene in the presence of either methyaluminoxane (MAO) or (AlBu3)-Bu-i/Ph3C+B(C6F5)(4)(-).