Cyclobutadiene Sandwich Complexes of Nickel and Iron from Cyclization of 1,3-Butadiene Dianions: Synthesis and Structural Characterization

Synthesis and structural study of cyclobutadiene sandwich transition metal complexes have been an interesting research area, because the cyclobutadiene, a well-recognized unstable anti-aromatic molecule, can be stabilized by coordination with a transition metal, forming stable cyclobutadiene sandwich complexes. Herein, we report the synthesis and structural characterization of novel cyclobutadiene sandwich transition metal complexes, including a cyclobutadiene/toluene iron complex 2, two cyclobutadiene/ferracyclopentadiene iron complexes 3, and a bis(cyclobutadiene) nickel complex 4. These complexes, structurally determined by single-crystal X-ray structural analysis, were all readily obtained from their corresponding metal halides and 1,4-dilithio-1,3-butadienes 1.