Bonding of imidazol-2-ylidene ligands in nickel complexes

The bonding of imidazol-2-ylidenes (H2Im) in a series of nickel complexes with seemingly different complex fragment group electronegativities, i.e., [Ni(H2Im)3], [Ni(H2Im)2], [Ni(H2Im)(CO)], [Ni(H2Im)(CO)2], and [Ni(H2Im)(CO)3], was analyzed. This series provides theoretical evidence that the bonding of imidazol-2-ylidene ligands to metal−complex fragments strongly depends on the nature of the ligand environment of the metal complex. An analysis of a series of isostructural complexes D2h- and D2d-M(H2Im)2 with different metals (M = Ni, Pd, Pt) reveals that the bonding also strongly depends on the metal used in the complex.