A Crystalline NiX<sub>6</sub> Complex

High-valent nickel species are implicated as intermediates\nin industrially\nrelevant chemical transformations and in the catalytic cycles of metalloenzymes.\nAlthough a small number of tetravalent NiX<sub>4</sub> complexes have\nbeen crystallographically characterized, higher nickel valence states\nhave not been identified. Here we report a stable, crystalline NiX<sub>6</sub> complex, Ni(BeCp)<sub>6</sub> (<b>1</b>; cyclopentadienyl\nanion (Cp)), formed by the insertion of zerovalent nickel into three\nBe–Be bonds. This 16-electron species features an inverted\nligand field, is diamagnetic, and exhibits <i>C</i><sub>3<i>v</i></sub> symmetry, on account of the lifting of\nNi 4<i>p</i>-orbital degeneracy in this molecular geometry.\nSingle-crystal X-ray diffraction and quantum chemical calculations\nboth reveal a toroidal band of electron density perpendicular to the <i>C</i><sub>3</sub> axis of the complex, which may be attributed\nto delocalized, multicenter aromatic NiBe<sub>6</sub> bonding.