Synthesis, Structural Characterisation and Reactivity of New Dinuclear Monocyclopentadienyl Imidoniobium and ‐tantalum Complexes − X‐ray Crystal Structures of [{Nb(η 5 ‐C 5 H 4 SiMe 3 )Cl 2 } 2 (μ‐1,4‐NC 6 H 4 N)], [{Ta(η 5 ‐C 5 Me 5 )Cl 2 } 2 (μ‐1,4‐NC 6 H 4 N)] and [{Ta(η 5 ‐C 5 Me 5 )(CH 2 SiMe 3 ) 2 } 2 (μ‐1,4‐NC 6 H 4 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 2 } 2 (μ‐1, i ‐NC 6 H 4 N)] [Cp′ = η 5 ‐C 5 H 4 SiMe 3 , M = Nb, i = 4 ( 1 ); Cp′ = η 5 ‐C 5 H 4 SiMe 3 , M = Nb, i = 3 ( 2 ); Cp′ = η 5 ‐C 5 H 4 SiMe 3 , M = Nb, i = 2 ( 3 ); Cp′ = η 5 ‐C 5 Me 5 , M = Nb, i = 4 ( 4 ); Cp′ = η 5 ‐C 5 Me 5 , M = Nb, i = 3 ( 5 ); Cp′ = η 5 ‐C 5 H 4 SiMe 3 , M = Ta, i = 4 ( 6 ); Cp′ = η 5 ‐C 5 H 4 SiMe 3 , M = Ta, i = 3 ( 7 )] were prepared by the reaction of one equivalent of the trichloro precursor [{MCl 3 } 2 (μ‐1, i ‐NC 6 H 4 N)] (M = Nb, Ta, i = 4, 3 or 2) with two equivalents of either C 5 H 4 (SiMe 3 ) 2 or C 5 Me 5 (SiMe 3 ). Complexes 1 − 7 can also be prepared by the reaction of two equivalents of [MCp′Cl 4 ] (Cp′ = η 5 ‐C 5 H 4 SiMe 3 , M = Nb, Ta; Cp′ = η 5 ‐C 5 Me 5 , 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 (μ‐1, i ‐NC 6 H 4 N)] [Cp′ = η 5 ‐C 5 Me 5 , i = 4 ( 8 ); Cp′ = η 5 ‐C 5 Me 5 , 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 (μ‐1, i ‐NC 6 H 4 N)] [Cp′ = η 5 ‐C 5 H 4 SiMe 3 , M = Nb, R = Me, i = 4 ( 10 ); Cp′ = η 5 ‐C 5 H 4 SiMe 3 , M = Nb, R = CH 2 SiMe 3 , i = 4 ( 11 ); Cp′ = η 5 ‐C 5 H 4 SiMe 3 , M = Nb, R = CH 2 Ph, i = 4 ( 12 ); Cp′ = η 5 ‐C 5 H 4 SiMe 3 , M = Nb, R = Me, i = 3 ( 13 ); Cp′ = η 5 ‐C 5 H 4 SiMe 3 , M = Nb, R = CH 2 SiMe 3 , i = 3 ( 14 ); Cp′ = η 5 ‐C 5 H 4 SiMe 3 , M = Nb, R = CH 2 Ph, i = 3 ( 15 ); Cp′ = η 5 ‐C 5 Me 5 , M = Ta, R = Me, i = 4 ( 16 ); Cp′ = η 5 ‐C 5 Me 5 , M = Ta, R = CH 2 SiMe 3 , i = 4 ( 17 ); Cp′ = η 5 ‐C 5 Me 5 , M = Ta, R = CH 2 Ph, i = 4 ( 18 )]. The alkylated complexes with other stoichiometries, [{M(Cp′)(Me)(X)} 2 (μ‐1,4‐NC 6 H 4 N)] [Cp = η 5 ‐C 5 H 4 SiMe 3 , M = Nb, X = Cl ( 19 ); Cp = η 5 ‐C 5 H 4 SiMe 3 , M = Nb, X = NMe 2 ( 20 ); Cp = η 5 ‐C 5 Me 5 , 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)