Modulating the reactivity of phosphanylidenephosphoranes towards water 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 exploiting their phosphinidenoid reactivity. Herein, we thoroughly show that a facile PMe 3 for H 2 O exchange gives access to various primary phosphine oxides of the general formula RP(H) 2 O (R = Mes*, Mes Ter, Dip Ter) and the molecular structure of Dip TerP(O)H 2 was determined. However, phosphanylidenephosphoranes are described to be highly nucleophilic as well. We show that the attachment of main group Lewis acids such as GaCl 3 and GaI 3 to R-P(PMe 3 ) yielded the highly sensitive, yet stable coordination compounds [(RPGaX 3 )PMe 3 ] (R = Mes*, Dip Ter) or [(RPPMe 3 ) 2 GaCl 2 ]GaCl 4 (R = Mes Ter). In contrast to the free phosphanylidenephosphoranes, these species reacted differently with H 2 O, which was demonstrated for [(Mes*PPMe 3 )GaI 3 ]. Here the formation of the phosphino-phosphonium cation [Mes*P(H)PMe 3 ] + and different anions was observed with combined NMR spectroscopic and SC-XRD (SC-XRD = single crystal X-ray diffraction analysis) studies. This work demonstrates that the ambiphilic character of phosphanylidenephosphoranes can be utilized to manipulate the reactivity of R-P(PMe 3 ) towards water, giving primary phosphine oxides, whereas the Lewis acid adducts [(RPGaX 3 )PMe 3 ] gave phosphino-phosphonium species.