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.