Fused Cyclic Carbodiphosphorane: Carbodiphosphorane- diphosphinocarbene Thermal Interconversion

All manipulations were performed under an inert atmosphere of argon using standard Schlenk techniques. Dry, oxygen-free solvents were employed. 1H, 13C, 31P NMR spectra were recorded on Bruker AC200, WM250 or Avance 300 spectrometers. IR spectra were recorded on a Perkin-Elmer 1600. 1H, 13C NMR chemical shift were reported in ppm relative to Me4Si as external standard. 31P NMR downfield chemical shift are expressed with a positive sign, in ppm, relative to standard of 85 % H3PO4. Carbodiphosphorane 1a was prepared by the previously reported method.[1] 2a: A benzene solution (1 mL) of 1a (0.05 g, 0.1 mmol) was heated at 80 °C for 60 h. After evaporation of the volatiles under vacuum, the brown solid was washed three times with pentane. Azaphosphete 2a was obtained as white crystals from a toluene solution at-30 °C (yield, 1.46g, 76%). M.p. 71-73 °C. 31P{1H} NMR (C6D6