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 .