Carbonyl complexes of niobium and tantalum and evidence of a niobium dinitrogen complex: the structure of carbonyldichlorocyclopentadienylbis(dimethylphenylphosphine)tantalum

Abstract

The reactions of [M(η-C₅H₅) Cl₄](M = Nb or Ta) with tertiary phosphines and other ligands and reduction of the products under carbon monoxide give carbonyls such as [M(η-C₅H₅)(CO)Cl₂(PR₃)₂](PR₃= tertiary phosphine), but no N₂ analogues. The crystal and molecular structure of [Ta(η-C₅H₅)(CO)Cl₂(PMe₂Ph)₂] has been determined by the heavy-atom method, using Mo-K_α radiation and 1 591 non-zero reflections. The space group is hexagonal P6₅, with a= 13.661 (2), c= 26.420(11)Å, and Z= 6. At convergence, R= 0.035 7 and R′= 0.037 0. Other carbonyls, such as [Nb(CO)₂Cl(Me₂PCH₂CH₂PMe₂)₂] are easily obtainable by reduction under CO, and the preparation of an impure dinitrogen complex which yields some hydrazine with acid is also described.