Synthesis and reactivity of new mono- and dinuclear niobium and tantalum imido complexes: X-ray crystal structure of [Ta(η 5-C 5H 4SiMe 3)Cl 2{ [dbnd]NC 6Me 4-4-(N(SiMe 3) 2)}

Abstract

The reaction of [1,4-{SiMe 3(H)N} 2C 6Me 4] ( 1) with 2 equivalents of LiBu n followed by the addition of SiMe 3Cl gave the diamine compound [1,4-{(SiMe 3) 2N} 2C 6Me 4] ( 2). [Ta(η 5-C 5H 4SiMe 3)Cl 4] reacts with 2, in a 2:1 stoichiometric ratio, to initially yield a mixture of the dinuclear, [{Ta(η 5-C 5H 4SiMe 3)Cl 2} 2(μ-1,4-NC 6Me 4N)] ( 3), and mononuclear, [Ta(η 5-C 5H 4SiMe 3)Cl 2{ NC 6Me 4-4-(N(SiMe 3) 2)}] ( 4), imido complexes. 3 can be obtained exclusively by submitting the reaction mixture to repeated cycles of evacuation, to remove volatiles, followed by addition of solvent and subsequent heating. The mononuclear imido complex 4 was isolated from the reaction of [Ta(η 5-C 5H 4SiMe 3)Cl 4] with 2 in a 1:1 stoichiometric ratio. The molecular structure of 4 was determined by X-ray diffraction studies. [TaCl 3(CH 3CN) 2{ NC 6Me 4-4-(N(SiMe 3) 2)}] ( 5) has been prepared by the reaction of one molar equivalent of TaCl 5 with 2 in a CH 3CN/CH 2Cl 2 solvent mixture. The synthesis of the niobium complexes, [{Nb(η 5-C 5H 4SiMe 3)Cl 2} 2(μ-1,4-NC 6Me 4N)] ( 6) and [Nb(η 5-C 5H 4SiMe 3)Cl 2{ NC 6Me 4-4-(N(SiMe 3) 2)}] ( 7), was achieved in a similar manner to their tantalum analogues. The reactivity of 7 towards nucleophilic reagents, namely lithium benzamidinate, lithium (trimethylsilyl)cyclopentadienyl or lithium dimethylamide, has been studied and the following compounds prepared:[Nb(η 5-C 5H 4SiMe 3)RCl{ NC 6Me 4-4-(N(SiMe 3) 2)}] (R = η 5-C 5H 4SiMe 3 ( 8), PhC(NSiMe 3) 2 ( 9), NMe 2 ( 10)). In an attempt to form the hetero bimetallic complex, [{Nb(η 5-C 5H 4SiMe 3)Cl 2}(μ-1,4-NC 6Me 4N){Ta(η 5-C 5H 4SiMe 3)Cl 2}] ( 11), the reaction of 7 with [Ta(η 5-C 5H 4SiMe 3)Cl 4] has been studied. Analysis of the reaction products showed that 11 may exist in equilibrium with the homo bimetallic complexes 3 and 6.