From a P‐Bridging Phosphaketene to μ‐Phosphinidenide and μ‐Diphosphaurea Units at a Dinickel Core

Salt metathesis of dinickel(II) complex LNi₂Br (1; L is a dinucleating pyrazolate ligand with two β‐diketiminato chelate arms) with Na(OCP) ⋅ (dioxane)₂.₅ yielded LNi₂(PCO) (2) with a P‐bridging phosphaethynolate. Further reaction of 2 with benzyl isocyanide or with an N‐heterocyclic carbene (NHC) triggered decarbonylation and gave LNi₂(PCN‐CH₂Ph) (3) and LNi₂P(NHC) (4) with P‐bridging cyanophosphide and NHC‐phosphinidenide, respectively. Electronic structure analysis indicated a μ₂‐η² : η¹ binding mode of the PCO⁻ anion between the two NiII ions in 2, which is even more pronounced for the [PCN(−CH₂Ph)]⁻ anion in 3. DFT assessment of the formation mechanism of 4 showed that attack at the phosphaketene‐C atom is kinetically preferred but reversible and unproductive, while kinetically more demanding back‐side SN2 attack at the phosphaketene‐P atom triggers CO release with 4 as thermodynamic product. Nucleophilic addition at the phosphaketene‐C could be demonstrated by the strongly exergonic reaction of 2 with KPPh₂, giving unstable K[LNi₂(P(O)CPPh₂)] (5) with a P‐bridging and K⁺‐stabilized diphosphaurea derivative. All new complexes 2–5 have been comprehensively characterized, including by X‐ray diffraction.