Triple-bond reactivity of an AsP complex intermediate: synthesis stemming from molecular arsenic, As(4).

While P(4) is the stable molecular form of phosphorus, a recent study illustrated the possibility of P(2) generation for reactions in organic media under mild conditions. The heavier group 15 element arsenic can exist as As(4) molecules, but As(4) cannot be stored as a pure substance because it is both light-sensitive and reverts thermally to its stable, metallic gray form. Herein we report As(4) activation giving rise to a mu-As(2) diniobium complex, serving in turn as precursor to a terminal arsenide anion complex of niobium. Functionalization of the latter provides the new AsPNMes* ligand, which when complexed with tungsten pentacarbonyl elicits extrusion of the (AsP)W(CO)(5) molecule as a reactive intermediate. Trapping reactions of the latter with organic dienes are found to furnish double Diels-Alder adducts in which the AsP unit is embedded in a polycyclic organic framework. Thermal generation of (AsP)W(CO)(5) in the presence of the neutral terminal phosphide complex P identical withMo(N[(i)Pr]Ar)(3) leads to the cyclo-AsP(2) complex (OC)(5)W(cyclo-AsP(2))Mo(N[(i)Pr]Ar)(3). The (AsP)W(CO)(5) trapping products were crystallized and characterized by X-ray diffraction methods, and computational methods were applied for analysis of the As-As and As-P bonds in the complexes.