Synthesis, Structural Characterisation and Reactivity of New Dinuclear Monocyclopentadienyl Imidoniobium and -tantalum Complexes − X-ray Crystal Structures of [{Nb(η<SUP>5</SUP>-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>)Cl<INF>2</INF>}<INF>2</INF>(μ-1,4-NC<INF>6</INF>H<INF>4</INF>N)], [{Ta(η<SUP>5</SUP>-C<INF>5</INF>Me<INF>5</INF>)Cl<INF>2</INF>}<INF>2</INF>(μ-1,4-NC<INF>6</INF>H<INF>4</INF>N)] and [{Ta(η<SUP>5</SUP>-C<INF>5</INF>Me<INF>5</INF>)(CH<INF>2</INF>SiMe<INF>3</INF>)<INF>2</INF>}<INF>2</INF>(μ-1,4-NC<INF>6</INF>H<INF>4</INF>N)]

The preparation of a family of dinuclear monocyclopentadienyl imidoniobium and -tantalum complexes was achieved by two different synthetic routes. The diimido complexes [{M(Cp')Cl<INF>2</INF>}<INF>2</INF>(μ-1,i-NC<INF>6</INF>H<INF>4</INF>N)] [Cp' = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Nb, i = 4 (1); Cp' = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Nb, i = 3 (2); Cp' = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Nb, i = 2 (3); Cp' = η⁵-C<INF>5</INF>Me<INF>5</INF>, M = Nb, i = 4 (4); Cp' = η⁵-C<INF>5</INF>Me<INF>5</INF>, M = Nb, i = 3 (5); Cp' = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Ta, i = 4 (6); Cp' = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Ta, i = 3 (7)] were prepared by the reaction of one equivalent of the trichloro precursor [{MCl<INF>3</INF>}<INF>2</INF>(μ-1,i-NC<INF>6</INF>H<INF>4</INF>N)] (M = Nb, Ta, i = 4, 3 or 2) with two equivalents of either C<INF>5</INF>H<INF>4</INF>(SiMe<INF>3</INF>)<INF>2</INF> or C<INF>5</INF>Me<INF>5</INF>(SiMe<INF>3</INF>). Complexes 1−7 can also be prepared by the reaction of two equivalents of [MCp'Cl<INF>4</INF>] (Cp' = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Nb, Ta; Cp' = η⁵-C<INF>5</INF>Me<INF>5</INF>, 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<INF>2</INF>}<INF>2</INF>(μ-1,i-NC<INF>6</INF>H<INF>4</INF>N)] [Cp' = η⁵-C<INF>5</INF>Me<INF>5</INF>, i = 4 (8); Cp' = η⁵-C<INF>5</INF>Me<INF>5</INF>, 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<INF>2</INF>}<INF>2</INF>(μ-1,i-NC<INF>6</INF>H<INF>4</INF>N)] [Cp' = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Nb, R = Me, i = 4 (10); Cp' = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Nb, R = CH<INF>2</INF>SiMe<INF>3</INF>, i = 4 (11); Cp' = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Nb, R = CH<INF>2</INF>Ph, i = 4 (12); Cp' = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Nb, R = Me, i = 3 (13); Cp' = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Nb, R = CH<INF>2</INF>SiMe<INF>3</INF>, i = 3 (14); Cp' = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Nb, R = CH<INF>2</INF>Ph, i = 3 (15); Cp' = η⁵-C<INF>5</INF>Me<INF>5</INF>, M = Ta, R = Me, i = 4 (16); Cp' = η⁵-C<INF>5</INF>Me<INF>5</INF>, M = Ta, R = CH<INF>2</INF>SiMe<INF>3</INF>, i = 4 (17); Cp' = η⁵-C<INF>5</INF>Me<INF>5</INF>, M = Ta, R = CH<INF>2</INF>Ph, i = 4 (18)]. The alkylated complexes with other stoichiometries, [{M(Cp')(Me)(X)}<INF>2</INF>(μ-1,4-NC<INF>6</INF>H<INF>4</INF>N)] [Cp = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Nb, X = Cl (19); Cp = η⁵-C<INF>5</INF>H<INF>4</INF>SiMe<INF>3</INF>, M = Nb, X = NMe<INF>2</INF> (20); Cp = η⁵-C<INF>5</INF>Me<INF>5</INF>, 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)