Studies of six-coordinate adducts all-trans-[M(OAr)2(X)2(L)2] (M=Nb, Ta; X=Cl, Br; L=tertiary phosphine, pyridine)

An extensive series of d1-derivatives of niobium and tantalum [M(OAr)2(X)2(L)2] (M=Nb, Ta; X=Cl, Br; L=tertiary phosphine, pyridine) have been isolated by reduction of the corresponding adducts [M(OAr)2(X)3(L)] in the presence of excess L. Crystallographic studies show an all-trans, octahedral arrangement of ligands about the metal center. The effect of the halide, donor ligand and aryloxide substituents upon the structural parameters is discussed.