Barrier to racemization in C3-symmetric complexes containing the hydrotris-(2-mercapto-1-ethylimidazolyl)borate [Tm(super ET)] ligand

The activation energies for the racemization of C3-symmetric complexes of four- and six coordinate metals with hydrotris(methimazolyl)borate lignad are explored by variable-temperature NMR and ab initio calculations. All of the four-coordinate complexes studied are found to follow a dissociative mechanism of racemization with activation energy dependent upon solvent donor ability.