On the ambiphilic character of phosphanylidenephosphoranes and manipulation of phosphinidenoid reactivity with Lewis acids

Phosphanylidenephosphoranes of the type R−P(PR’3), also known as phospha-Wittig reagents, can be utilized in a variety of bond activation reactions pursuing their phosphinidenoid reactivity. In here, we thoroughly show that a facile PMe3 for H2O exchange gives access to various primary phosphine oxides of the general formula RP(H)2O (R = Mes*, MesTer, DipTer). The molecular structure of DipTerP(H)2O was determined and provided the first picture of such species in the solid state. However, phosphanylidenephosphoranes are described to be highly nucleophilic as well. We show that the attachment of main group Lewis acids such as GaCl3 and GaI3 to2 R−P(PMe3) yielded highly sensitive, yet stable coordination compounds [RP(GaX3)PMe3] (R = Mes*, DipTer) or [(RPPMe3)2GaCl2]GaCl4 (R = MesTer). In contrast to the free phosphanylidenephosphoranes, these species reacted differently with H2O which was demonstrated for [(Mes*PPMe3)GaI3]. Here the formation of the phosphinophosphonium cation [Mes*P(H)PMe3]+ and different anions was observed with combined NMR spectroscopic and SC-XRD (SC-XRD = single crystal diffraction analysis) studies. This work demonstrates that the ambiphilic character of phosphanylidenephosphoranes can be utilized to manipulate the reactivity of R−P(PMe3) towards water, giving primary phosphine oxides, whereas the Lewis acid adducts [(RPPMe3)GaX3] gave phosphino-phosphonium species.