Crystal structure of the phosphanylidene-σ4-phosphorane DmpPPMe3 (Dmp=2,6-Mes2C6H3) and reactions with electrophiles

The stable phosphanylidene-σ4-phosphorane DmpPPMe3 (1, Dmp=2,6-Mes2C6H3) has been examined by single-crystal X-ray diffraction methods. The structure of 1 features a relatively short PP bond length of 2.084(2) Å. Reactions of 1 with various electrophiles demonstrate the nucleophilic behavior of the phosphanylidene atom of 1 and also provide access to new organophosphorus compounds. For example, addition of excess BH3 (in the form of either BH3·THF or BH3·SMe2) to 1 leads to formation of a mono-borane adduct DmpP(BH3)PMe3. Reactions of carbon and silicon based electrophiles EX (E=R3C or R3Si; X=halide or OTf−) produce either diphosphanium salts [DmpP(E)PMe3]X or phosphines DmpP(E)X. In some cases equilibrium mixtures of both product types are observed, and the equilibria can be shifted by addition of either X− or PMe3. Compound 1 is also readily protonated by HOTf, HCl and PhOH. As found for the carbon and silicon based electrophiles, the nature of the resulting product depends on the counterion.