Phosphorus stabilized carbenes: theoretical predictions

B3LYP/6-311+G** and B3LYP/3-21G(*) isodesmic stabilization energies of several five and six membered cyclic carbenes containing phosphorus were calculated to estimate their stability against dimerization. Bridgehead tricoordinate phosphorus in α-position from the carbene increases the stability. Tetracoordinate phosphorus, in β-position from the divalent carbon (forming a phosphorus ylide) has also a significant stabilizing effect. The combination of the above effects results in systems, which are likely to be synthesizable, their stabilization energy approaching that of the Arduengo carbene.