Group 5 imido complexes derived from diamido-pyridine ligands

Reaction of the vanadium(V) imide [V(NAr)Cl-3(THF)] (Ar = 2,6-(C6H3Pr2)-Pr- i) with the diamino-pyridine derivative MeC(2-C5H4N)(CH2NHSiMe2' BU)(2) (ab breviated as H2N ' N-2(py)) gave modest yields of the vanadium(IV) species [V(NAr)(H3N 'N "N-py)Cl-2] (1 where H3N 'N "N-py = MeC(2- C5H4N)(CH2NH2)(CH 2NHSiMe2' Bu) in which the original H2N ' N-2(py) has effectively lost SiMe 2' Bu (as ClSiMe2' Bu) and gained an H atom. Better behaved reactions were found between the heavier Group 5 metal complexes [M(NR)Cl-3((py))(2)] (M = Nb or Ta, R = ' Bu or Ar) and the dilithium salt Li-2[N2Npy] (where H2N2Np y = MeC(2-C5H4N)(CH2NHSiMe3)(2)), and these yielded the six-coordinate M(V) complexes [M(NR)Cl(N2Npy)(py)] (M = Nb, R = Bu-t 2; M = Ta, R = Bu-t 3 or Ar 4). The compounds 2-4 are fluxional in solution and undergo dynamic exch ange processes via the corresponding five-coordinate homologues [M(NR)Cl(N2 Npy)]. Activation parameters are reported for the complexes 2 and 3. In the case of 2, high vacuum tube sublimation afforded modest quantities of [Nb( (NBu)-Bu-t)Cl(N2Npy)] (5). The X-ray crystal structures of the four compoun ds 1, 2, 3, and 4 are reported.