Inverse-Sandwich Cyclobutadiene Dinickel Complexes: Synthesis and Structural Characterization

Synthesis and structural characterization of inverse-sandwich complexes, whose planar conjugated ligand is a cyclobutadiene, have attracted much attention for their unique chemical bonding modes and synthetic methods. In this article, a new class of inverse sandwich cyclobutadiene dinickel complexes, the first case of inverse sandwich cyclobutadiene complexes with transition metals, were synthesized from the reaction of dilithio reagents with NiBr2. Magnetometry and DFT calculations have revealed that the two nickel centers have antiferromagnetic coupling with each other and there exists electron back donation from the Ni(3d) orbitals to the pi* orbital of the cyclobutadiene ligand. Besides, the inverse sandwich cyclobutadiene dinickel complex could be reversed, being transformed to its corresponding normal sandwich complex, the bis(cyclobutadiene) nickel complex.