Group 5 imido complexes supported by diamido-pyridine ligands: Aryloxide, amide, benzamidinate, alkyl, and cyclopentadienyl derivatives

A family of new organometallic and coordination group 5 compounds supported by an imido-diamido-pyridine ligand set are reported. Reaction of [M(NR)Cl (kappa (3)-N2Npy)(py)] (M = Nb, R = Bu-t 1; M = Ta, R = Bu-t 2 or Ar 3, whe re N2Npy = MeC(2-C5H4N)(CH2NSiMe3)(2) and Ar = 2,6-(C6H3Pr2)-Pr-i) with LiO Ar or LiPhC(NSiMe3)(2) afforded the five-coordinate aryloxide and benzamidi nate complexes [M(NR)(OAr)(kappa (3)-N2Npy)] (R = tBu, M = Nb 4 or Ta 5; R = Ar, M = Ta 6) and [Nb((NBu)-Bu-t){PhC(NSiMe3)(2)}(kappa (3)-N2Npy)] (7), respectively. Reaction of 1 or 2 with LiN(SiMe3)(2) or LiCH(SiMe3)(2) gave the four-coordinate compounds [M((NBU)-B-t)(X)(kappa (2)-N2Npy)] (M = Nb, X = N(SiMe3)(2) 8 or CH(SiMe3)(2) 9; M = Ta, X = CH(SiMe3)(2) 10). Reaction of I or 2 with the less sterically demanding alkyl reagent LiCH2SiMe3 gave, in the case of niobium, only the four-coordinate [M((NBu)-Bu-t)(CH2SiMe3)( kappa (2)-N2Npy)] (11), but for tantalum an equilibrium mixture of four- (k appa (2)-) and five- (kappa (3)-) coordinate isomers was identified by NMR spectroscopy. Reaction of 1 with PhCH2MgCl or LiC5H4Me gave the correspondi ng eta (1)- or eta (5)-hydrocarbyl complexes [Nb((NBu)-Bu-t)(CH2Ph)(kappa ( 3)-N2Npy)(py)] (13) and [Nb((NBu)-Bu-t)(eta (5)-C5H4Me)-(kappa (2)-N2Npy)] (14). The X-ray crystal structures of the compounds 4, 6, and 9 are reporte d.