Triple-Bond Reactivity of an AsP Complex Intermediate: Synthesis Stemming from Molecular Arsenic, As-4

Abstract

While P[subscript 4] is the stable molecular form of phosphorus, a recent study illustrated the possibility of P[subscript 2] generation for reactions in organic media under mild conditions. The heavier group 15 element arsenic can exist as As[subscript 4] molecules, but As[subscript 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 As4 activation giving rise to a μ-As[subscript 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)[subscript 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)[subscript 5] in the presence of the neutral terminal phosphide complex P≡Mo(N[iPr]Ar)[subscript 3] leads to the cyclo-AsP[subscript 2] complex (OC)[subscript 5]W(cyclo-AsP2)Mo(N[iPr]Ar)[subscript 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.