C‐Halophosphaalkenes: Probing the range of stability and reactivity towards bromine

Abstract

Abstract The importance of steric protection for the stability of phosphaalkenes RP=CI 2 ( 6 ) was investigated by varying the size of group R. The phosphaalkene IsP=CI 2 ( 6b ) (Is = 2,4,6‐triisopropylphenyl) could be prepared in 15% isolated yield by reaction of IsPCl 2 and HCI 3 with two equivalents of lithium diisopropylamide, in analogy to the synthesis of the stable, sterically more protected, Mes*P = CI 2 ( 6a ) (Mes* = 2,4,6‐tri‐tert‐butylphenyl). If the steric protection on the phosphorus was decreased further (R = Es = 2,4,6‐triethylphenyl, R = Mes = 2,4,6‐trimethylphenyl), the substitution products RP(Cl)N(Pr i ) 2 (R = Es ( 9c ) or Mes ( 9d )) were formed as main products, in addition to thermally unstable phosphaalkenes EsP=CI 2 ( 6c ) and MesP=CI 2 ( 6d ). The structures of 9c‐d were corroborated by independent synthesis from RPCl 2 and two equivalents of diisopropylamine. The reaction of 6a with bromine gave an E/Z mixture of the C‐bromo‐C‐iodophosphaalkene (EZ)‐Mes* P = CBrI (E/Z‐ 10 ). Further reaction with bromine proceeded via Mes*P=CBr 2 ( 5a ) and finally led to Mes* P(Br)(CHBr 2 ) ( 12 ).