Haptotropism in a Nickel Complex with a Neutral, π‐Bridging cyclo‐P(4) Ligand Analogous to Cyclobutadiene

Dedicated to Professor Manfred Scheer on the occasion of his 65th birthday The reaction of (1)Ni(η(2)‐cod), 2, incorporating a chelating bis(N‐heterocyclic carbene) 1, with P(4) in pentane yielded the dinuclear complex [(2)Ni](2)(μ(2),η(2) : η(2)‐P(4)), 3, formally featuring a cyclobutadiene‐like, neutral, rectangular, π‐bridging P(4)‐ring. In toluene, the butterfly‐shaped complex [(1)Ni](2)(μ(2),η(2) : η(2)‐P(2)), 4, with a formally neutral P(2)‐unit was obtained from 2 and either P(4) or 3. Computational studies showed that a haptotropic rearrangement involving two isomers of the μ(2),η(2) : η(2)‐P(4) coordination mode and a low‐energy μ(2),η(4) : η(4)‐P(4) coordination mode, as previously predicted for related nickel cyclobutadiene complexes, could explain the coalescence observed in the low‐temperature NMR spectra of 3. The insertion of the (1)Ni fragment into a P−P bond of P(7)(SiMe(3))(3), forming complex 5 with a norbornane‐like P(7) ligand, was also observed.