Bis(methylen)phosphorane — Synthese, spektroskopische Untersuchungen und thermische Isomerisierungen zu λ 3 ‐Phosphiranen

Bis(methylene)phosphoranes – Synthesis, Spectroscopic Investigations and Thermal Isomerizations to λ 3 ‐Phosphiranes A great number of differently substituted bis(methylene)phosphoranes 10 [R – P{ = C(SiMe 3 ) 2 } 2 ] are obtained by nucleophilic substitution from bis[bis(trimethylsilyl)methylene]‐chlorophosphorane ( 8 ). The reactions of dichlorophosphanes 1 and methylenephosphanes 3 with lithium carbenoides 2 furnish the mixed derivatives 6 [R—P( = CR 1 R 2 )( = CR 3 R 4 )] and 7 [R—P( = C(SiMe 3 ) 2 ( = CR 3 R 4 )]. Among these the reaction of the sterically less hindered methylenephosphanes 3c, d [R 2 N—P = C(H)SiMe 3 , R = Et, i Pr] with an excess of the lithium carbenoide 2b results in the formation of the σ 4 λ 5 ‐phosphiranes 11a, b {R 2 N – P[ = C(H)SiMe 3 ] 2 }. The sterically highly demanding substituents in 10a – o render great thermal stability, while the mixed bis(methylene)phosphoranes 6, 7 rearrange to the corresponding σ 4 λ 5 ‐phosphiranes 15a–o . Investigations performed between 30 and 180°C reveal that all bis(methylene)phosphoranes, with the exception of 6c, k – m and 7e , can be isomerized. – The phosphino‐substituted bis(methylene)phosphoranes 10k, 1 show different reactivity. Light‐and thermally induced cleavage of the P – P bond, and dimerization of the corresponding fragments result in the formation of 14 and the diphosphanes 13a, b . The bis(methylene)phosphoranes 10a–o are investigated by UV and NMR spectroscopy.