Synthesis of Phosphorus(V)-Stabilized Geminal Dianions. The Cases of Mixed P=X/P→BH3 (X = S, O) and P=S/SiMe3 Derivatives

The monodeprotonation of [CH2(PPh2 -> BH3)(PPh2=E)] (E = S (6), O (7)) afforded [CH(PPh2 -> BH3)(PPh2=-E)](-) (E = S (6(-)), O (7(-))), whose structures were confirmed by X-ray crystallography. The kinetics of the second deprotonation appeared to be crucial in efficient synthesis of the corresponding dianions. Thus, the double deprotonation of 6 only led to 6(2-); the analogous reaction with 7 was slower and resulted only in the partial formation of 7(2-). Double deprotonation of the compound [CH2(SiMe3)-(PPh2=S)] (8) also resulted in the partial formation of (C(SiMe3)(PPh2=S)](2-) (8(2-)), whose structure was confirmed by X-ray crystallography. The rare monomeric Mg carbene compound [MgC(PPh2 -> BH3)(PPh2=S)] (9) was obtained by the reaction of 6 with Mg(nBu)(2). The X-ray structure of 9 is presented.