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

Abstract

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.