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(N 2 C 3 H 3 )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(N 2 C 3 H 3 ) 3 ] 2 M (M = Mn, Fe, Co, Ni, Cu, Zn), believed to possess an octahedral MN 6 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 η 5 -C 5 H 5 ligand. From ir measurements and bond length data it appears that the [MeGa(N 2 C 3 H 3 ) 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(N 2 C 3 H 3 ) 3 ]Mo(CO) 2 (η 3 -C 3 H 5 ). Crystals of this complex are tetragonal, a = 26.217(3), c = 10.723(2) Å, Z = 16, space group I4 1 /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 R w of 0.031 for 2582 reflections with I ≥ 3σ(I).