The
2-phosphaethynolate (OCP) anion has found versatile applications
across the periodic table but remains underexplored in group 2 chemistry
due to challenges in isolating thermally stable complexes. By rationally
modifying their coordination environments using 1,3-dialkyl-substituted
N-heterocyclic carbenes (NHCs), we have now isolated and characterized
thermally stable, structurally diverse, and hydrocarbon soluble magnesium
phosphaethynolate complexes (2, 4
Me
, and 8–10), including the novel
phosphaethynolate Grignard reagent (2
iPr
). The methylmagnesium phosphaethynolate and magnesium diphosphaethynolate
complexes readily activate dioxane with subsequent H-atom abstraction
to form [(NHC)MgX(μ-OEt)]2 [X = Me (3) or OCP (8 and 9)] complexes. Their reactivities
increased with the Lewis acidity of the Mg2+ cation and
may be attenuated by Lewis base saturation or a slight increase in
carbene sterics. Solvent effects were also investigated and led to
the surreptitious isolation of an ether-free sodium phosphaethynolate
(NHC)3Na(OCP) (6), which is soluble in aromatic
hydrocarbons and can be independently prepared by the reaction of
NHC and [Na(dioxane)2][OCP] in toluene. Under forcing conditions
(105 °C, 3 days), the magnesium diphosphaethynolate complex (NHC)3Mg(OCP)2 (10) decomposes to a mixture
of organophosphorus complexes, among which a thermal decarbonylation
product [(NHC)2PI][OCP] (11) was
isolated.