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(κ 3 -N 2 N py )(py)] (M = Nb, R = t Bu 1; M = Ta, R = t Bu 2 or Ar 3, where N 2 N py = MeC(2-C 5 H 4 N)(CH 2 NSiMe 3 ) 2 and Ar = 2,6-C 6 H 3 i Pr 2 ) with LiOAr or LiPhC(NSiMe 3 ) 2 afforded the five-coordinate aryloxide and benzamidinate complexes [M(NR)(OAr)(κ 3 -N 2 N py )] (R = t Bu, M = Nb 4 or Ta 5; R = Ar, M = Ta 6 ) and [Nb(N t Bu){PhC(NSiMe 3 ) 2 }(κ 3 -N 2 N py )] ( 7 ), respectively. Reaction of 1 or 2 with LiN(SiMe 3 ) 2 or LiCH(SiMe 3 ) 2 gave the four-coordinate compounds [M(N t Bu)(X)(κ 2 -N 2 N py )] (M = Nb, X = N(SiMe 3 ) 2 8 or CH(SiMe 3 ) 2 9; M = Ta, X = CH(SiMe 3 ) 2 10 ). Reaction of 1 or 2 with the less sterically demanding alkyl reagent LiCH 2 SiMe 3 gave, in the case of niobium, only the four-coordinate [M(N t Bu)(CH 2 SiMe 3 )(κ 2 -N 2 N py )] ( 11 ), but for tantalum an equilibrium mixture of four- (κ 2 -) and five- (κ 3 -) coordinate isomers was identified by NMR spectroscopy. Reaction of 1 with PhCH 2 MgCl or LiC 5 H 4 Me gave the corresponding η 1 - or η 5 -hydrocarbyl complexes [Nb(N t Bu)(CH 2 Ph)(κ 3 -N 2 N py )(py)] ( 13 ) and [Nb(N t Bu)(η 5 -C 5 H 4 Me)(κ 2 -N 2 N py )] ( 14 ). The X-ray crystal structures of the compounds 4, 6, and 9 are reported.