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 imidomobium and -tantalum complexes was achieved by two different synthetic routes. The diimido complexes [{M(Cp')Cl-2}(2)(mu-1,i-NC6H4N)] [Cp' = eta(5)-C5H4SiMe3, M = Nb, i = 4 (1); Cp' = eta(5)-C5H4SiMe3, M = Nb, i = 3 (2); Cp' = eta(5)-C5H4SiMe3, M = Nb, i = 2 (3); Cp' = eta(5)-C5Me5, M = Nb, i = 4 (4); Cp' = eta(5)-C5Me5, M = Nb, i = 3 (5); Cp' = eta(5)-C5H4SiMe3, M = Ta, i = 4 (6); Cp' = eta(5)-C5H4SiMe3, M = Ta, i = 3 (7)] were prepared by the reaction of one equivalent of the trichloro precursor [{MCl3}(2)(mu-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'Cl-4] (Cp' = eta(5)-C5H4SiMe3, M = Nb, Ta; Cp' = eta(5)-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')Cl-2}(2)(mu-1,i-NC6H4N)] [Cp' = eta(5)-C5Me5, i = 4 (8); Cp' = eta(5)-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')R-2}(2)(mu-1,i-NC6H4N)] [Cp' = eta(5)-C5H4SiMe3, M = Nb, R = Me, i = 4 (10); Cp' = eta(5)-C5H4SiMe3, M = Nb, R = CH2SiMe3, i = 4 (11); Cp' = eta(5)-C5H4SiMe3, M = Nb, R = CH2Ph, i = 4 (12); Cp' = eta(5)-C5H4SiMe3, M = Nb, R = Me, i = 3 (13); Cp' = eta(5)-C5H4SiMe3, M = Nb, R = CH2SiMe3, i = 3 (14); Cp' = eta(5)-C5H4SiMe3, M = Nb, R = CH2Ph, i = 3 (15); Cp' = eta(5)-C5Me5, M = Ta, R = Me, i = 4 (16); Cp' = eta(5)-C5Me5, M = Ta, R = CH2SiMe3, i = 4 (17); Cp' = eta(5)-C5Me5, M = Ta, R = CH2Ph, i = 4 (18)]. The alkylated complexes with other stoichiometries, [{M(Cp')(Me)(X)}(2)(mu-1,4-NC6H4N)] [Cp = eta(5)-C5H4SiMe3, M = Nb, X = Cl (19); Cp = eta(5)-C5H4SiMe3, M = Nb, X = NMe2 (20); Cp = eta(5)-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. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.