Synthesis and Reactivity of Nickel‐Stabilised μ2:η2,η2‐P2, As2 and PAs Units

The reactivity of two paramagnetic nickel(I) compounds, CpNi(NHC) (where Cp=cyclopentadienyl; NHC=1,3‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene (IMes) or 1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene (IPr)), towards [Na(dioxane)x][PnCO] (Pn=P, As) is described. These reactions afford symmetric bimetallic compounds (μ2:η2,η2‐Pn2){Ni(NHC)(CO)}2. Several novel intermediates en route to such species are identified and characterised, including a compound containing the PCO− anion in an unprecedented μ2:η2,η2‐binding mode. Ultimately, on treatment of the (μ2:η2,η2‐Pn2){Ni(IMes)(CO)}2 compounds with carbon monoxide, the Pn2 units can be released, affording P4 in the case of the phosphorus‐containing species, and elemental arsenic in the case of (μ2:η2,η2‐As2){Ni(IMes)(CO)}2.