Novel isolable C,C-dichlorophosphaalkenes RP=CCl2 owing to the use of new huge stabilizing groups

Three new C,C-dichlorophosphaalkenes RP=CCl2 18-20 have been synthesized fr om the corresponding dichlorophosphines RPCl2 11-13. Compounds 18-20 are st abilized owing to the use of thr very bulky new groups R-1 [2,6-bis(4-methy lphenyl)-4-methylphenyl] and R-3 [2;6-bis(2-methoxyphenyl)-4-methylphenyl] and the known 2,6-dimesityl-4-methylphenyl (R-2). The compounds with a R-3 group ((RI)-I-3: 4, (RPCl2)-P-3: 13, (RPH2)-P-3: 17 and (RP)-P-3=CCl2: 20) exist in the form of two conformational isomers on the NMR time scale. A H- 1 and P-31 NMR dynamic study (for 4 and 13 respectively) allowed the determ ination of the Delta G* of this phenomenon, respectively 18.5 and 18.2 kcal /mol.