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

The stable phosphanylidene-sigma(4)-phosphorane DmpP=PMe3 (1, Dmp = 2,6-Mes(2)C(6)H(3)) 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) Angstrom. 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. (C) 2000 Elsevier Science S.A. All rights reserved.