Synthesis, Structural Characterisation and Reactivity of New Dinuclear Monocyclopentadienyl Imidoniobium and -tantalum Complexes − X-ray Crystal Structures of [{Nb(η5-C5H4SiMe3)Cl2}2(μ-1,4-NC6H4N)], [{Ta(η5-C5Me5)Cl2}2(μ-1,4-NC6H4N)] and [{Ta(η5-C5Me5)(CH2SiMe3)2}2(μ-1,4-NC6H4N)]

The preparation of a family of dinuclear monocyclopentadienyl imidoniobium and -tantalum complexes was achieved by two different synthetic routes. The diimido complexes [{M(Cp′)Cl2}2(μ-1,i-NC6H4N)] [Cp′ = η5-C5H4SiMe3, M = Nb, i = 4 (1); Cp′ = η5-C5H4SiMe3, M = Nb, i = 3 (2); Cp′ = η5-C5H4SiMe3, M = Nb, i = 2 (3); Cp′ = η5-C5Me5, M = Nb, i = 4 (4); Cp′ = η5-C5Me5, M = Nb, i = 3 (5); Cp′ = η5-C5H4SiMe3, M = Ta, i = 4 (6); Cp′ = η5-C5H4SiMe3, M = Ta, i = 3 (7)] were prepared by the reaction of one equivalent of the trichloro precursor [{MCl3}2(μ-1,i-NC6H4N)] (M = Nb, Ta, i = 4, 3 or 2) with two equivalents of either C5H4(SiMe3)2 or C5Me5(SiMe3). Complexes 1−7 can also be prepared by the reaction of two equivalents of [MCp′Cl4] (Cp′ = η5-C5H4SiMe3, M = Nb, Ta; Cp′ = η5-C5Me5, M = Nb, Ta) with one equivalent of the corresponding aniline compound, N,N,N′,N′-tetrakis(trimethylsilyl)-1,4-, -1,3-, or -1,2-phenylenediamine, respectively. The synthesis of [{Ta(Cp′)Cl2}2(μ-1,i-NC6H4N)] [Cp′ = η5-C5Me5, i = 4 (8); Cp′ = η5-C5Me5, i = 3 (9)] was only successful with the second preparative method. The reaction of 1, 2 and 8 with alkylating reagents gave the corresponding tetraalkyl derivatives, [{M(Cp′)R2}2(μ-1,i-NC6H4N)] [Cp′ = η5-C5H4SiMe3, M = Nb, R = Me, i = 4 (10); Cp′ = η5-C5H4SiMe3, M = Nb, R = CH2SiMe3, i = 4 (11); Cp′ = η5-C5H4SiMe3, M = Nb, R = CH2Ph, i = 4 (12); Cp′ = η5-C5H4SiMe3, M = Nb, R = Me, i = 3 (13); Cp′ = η5-C5H4SiMe3, M = Nb, R = CH2SiMe3, i = 3 (14); Cp′ = η5-C5H4SiMe3, M = Nb, R = CH2Ph, i = 3 (15); Cp′ = η5-C5Me5, M = Ta, R = Me, i = 4 (16); Cp′ = η5-C5Me5, M = Ta, R = CH2SiMe3, i = 4 (17); Cp′ = η5-C5Me5, M = Ta, R = CH2Ph, i = 4 (18)]. The alkylated complexes with other stoichiometries, [{M(Cp′)(Me)(X)}2(μ-1,4-NC6H4N)] [Cp = η5-C5H4SiMe3, M = Nb, X = Cl (19); Cp = η5-C5H4SiMe3, M = Nb, X = NMe2 (20); Cp = η5-C5Me5, M = Ta, X = Cl (21)], were also prepared. The molecular structures of complexes 1, 8 and 17 were determined by single-crystal X-ray diffraction studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)