Syntheses and crystal structures of phenyl(2-pyridyl)amido complexes of zirconium(IV), niobium(V) and tantalum(V)

Di-mu-chloro-dichlorotetrakis[phenyl(2-pyridyl)amido]dizirconium(IV), trichlorobis[phenyl(2-pyridyl)amido]niobium(V) and trichlorobis[phenyl(2-pyridyl)amido]tantalum(V) have been synthesized in a direct reaction between 2-(phenylamino)pyridine and the appropriate metal halide under reflux in toluene. The use of butyllithium was rejected because of the formation of the unreactive ligand adduct bis[2-(phenylamino)pyridine]bis[phenyl(2-pyridyl)amido]dilithium. Single-crystal structures were determined for all four compounds. The niobium and tantalum complexes are monomeric in the solid state, whereas the zirconium complex is a dimer with two bridging chloride ligands. The amide is didentate with one sigma- and one pi-donor bond. The chelate rings formed have narrow N-M-N angles, around 60 degrees. The co-ordination spheres around the transition metals are pseudo-pentagonal bipyramids.