Synthesis and reactivity of new mono- and dinuclear niobium and tantalum imido complexes: X-ray crystal structure of [Ta(η5-C5H4SiMe3)Cl2{NC6Me4-4-(N(SiMe3)2)}]

The reaction of [1,4-{SiMe 3 (H)N} 2 C 6 Me 4 ] ( 1 ) with 2 equivalents of LiBu n followed by the addition of SiMe 3 Cl gave the diamine compound [1,4-{(SiMe 3 ) 2 N} 2 C 6 Me 4 ] ( 2 ). [Ta(η 5 -C 5 H 4 SiMe 3 )Cl 4 ] reacts with 2 , in a 2:1 stoichiometric ratio, to initially yield a mixture of the dinuclear, [{Ta(η 5 -C 5 H 4 SiMe 3 )Cl 2 } 2 (μ-1,4-NC 6 Me 4 N)] ( 3 ), and mononuclear, [Ta(η 5 -C 5 H 4 SiMe 3 )Cl 2 { NC 6 Me 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 5 H 4 SiMe 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 3 CN) 2 { NC 6 Me 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 3 CN/CH 2 Cl 2 solvent mixture. The synthesis of the niobium complexes, [{Nb(η 5 -C 5 H 4 SiMe 3 )Cl 2 } 2 (μ-1,4-NC 6 Me 4 N)] ( 6 ) and [Nb(η 5 -C 5 H 4 SiMe 3 )Cl 2 { NC 6 Me 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 5 H 4 SiMe 3 )RCl{ NC 6 Me 4 -4-(N(SiMe 3 ) 2 )}] (R = η 5 -C 5 H 4 SiMe 3 ( 8 ), PhC(NSiMe 3 ) 2 ( 9 ), NMe 2 ( 10 )). In an attempt to form the hetero bimetallic complex, [{Nb(η 5 -C 5 H 4 SiMe 3 )Cl 2 }(μ-1,4-NC 6 Me 4 N){Ta(η 5 -C 5 H 4 SiMe 3 )Cl 2 }] ( 11 ), the reaction of 7 with [Ta(η 5 -C 5 H 4 SiMe 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 .