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 .