Synthesis and reactivity of cyclobutadiene nickel bromide

Abstract

NiBr₂ reacts with 3-hexyne in the presence of Mg and EtOH to give the cyclobutadiene bromide complex [(C₄Et₄)NiBr₂]₂, which serves as a general precursor for various cyclobutadiene nickel compounds. In particular, complexes with 2-electron ligands (C₄Et₄)Ni(L)Br₂ (L = PPh₃, P(OMe)₃, pyridine), complexes with bidentate ligands [(C₄Et₄)Ni(L₂)Br]PF₆ (L₂ = bipyridine, phenanthroline), and nickelacarborane (C₄Et₄)NiC₂B₉H₁₁ were obtained from [(C₄Et₄)NiBr₂]₂ in 70–95% yields. The reactions of [(C₄Et₄)NiBr₂]₂ with an excess of strong ligands, such as ^tBuNC or dppe, led to the displacement of cyclobutadiene. The structures of the five compounds have been established by X-ray diffraction analysis. The previously reported data on cyclobutadiene nickel complexes have been also reviewed.