Group 5 Imido Complexes Derived from Diamido-Pyridine Ligands

Reaction of the vanadium(V) imide [V(NAr)Cl3(THF)] (Ar = 2,6-C6H3iPr2) with the diamino-pyridine derivative
MeC(2-C5H4N)(CH2NHSiMe2tBu)2 (abbreviated as H2N‘2Npy) gave modest yields of the vanadium(IV) species
[V(NAr)(H3N‘N‘ ‘Npy)Cl2] (1 where H3N‘N‘ ‘Npy = MeC(2- C5H4N)(CH2NH2)(CH2NHSiMe2tBu) in which the
original H2N‘2Npy has effectively lost SiMe2tBu (as ClSiMe2tBu) and gained an H atom. Better behaved reactions
were found between the heavier Group 5 metal complexes [M(NR)Cl3(py)2] (M = Nb or Ta, R = tBu or Ar) and
the dilithium salt Li2[N2Npy] (where H2N2Npy = MeC(2-C5H4N)(CH2NHSiMe3)2), and these yielded the six-coordinate M(V) complexes [M(NR)Cl(N2Npy)(py)] (M = Nb, R = tBu 2; M = Ta, R = tBu 3 or Ar 4). The
compounds 2−4 are fluxional in solution and undergo dynamic exchange processes via the corresponding five-coordinate homologues [M(NR)Cl(N2Npy)]. Activation parameters are reported for the complexes 2 and 3. In the
case of 2, high vacuum tube sublimation afforded modest quantities of [Nb(NtBu)Cl(N2Npy)] (5). The X-ray
crystal structures of the four compounds 1, 2, 3, and 4 are reported.