Synthesis and coordinating properties of the anionic tridentate ligand, methyl tris(1-pyrazolyl)gallate, [MeGa(N2C3H3)3]−. X-ray crystal structure of [MeGa(N2C3H3)3]Mo(CO)2(η3-C3H5)

Abstract

The anionic tridentate ligand, [MeGa(N2C3H3)3]−, has been characterized and its coordinating properties studied. It acts as a six-electron chelating ligand to divalent transition metal ions giving complexes of the type, [MeGa(N2C3H3)3]2M (M = Mn, Fe, Co, Ni, Cu, Zn), believed to possess an octahedral MN6 core. The ligand also forms numerous carbonyl complexes and its coordinating ability in Mo, W, and Mn carbonyl derivatives is compared with that of similar boron ligands and the η5-C5H5 ligand. From ir measurements and bond length data it appears that the [MeGa(N2C3H3)3]− ligand is superior in creating an electron-rich transition metal centre, and it also affords greater steric protection for the central metal. The expected tridentate chelating nature of the new ligand has been demonstrated through a crystal structure determination of the complex [MeGa(N2C3H3)3]Mo(CO)2(η3-C3H5). Crystals of this complex are tetragonal, a = 26.217(3), c = 10.723(2) Å, Z = 16, space group I41/a. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix least-squares procedures to a final R of 0.030 and Rw of 0.031 for 2582 reflections with I ≥ 3σ(I).