BIS(METHYLENE)PHOSPHORANES - SYNTHESIS, SPECTROSCOPIC INVESTIGATIONS AND THERMAL ISOMERIZATIONS TO LAMBDA-3-PHOSPHIRANES

A great number of differently substituted bis(methylene)phosphoranes 10 [R-P{ = C(SiMe3)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(= CR1R2)(= CR3R4)] and 7 [R-P(= C(SiMe3)2(= CR3R4)]. Among these the reaction of the sterically less hindered methylenephosphanes 3c,d [R2N-P = C(H)SiMe3, R = Et, iPr] with an excess of the lithium carbenoide 2b results in the formation of the sigma(4)lambda(5)-phosphiranes 11a,b {R2N-P[= C(H)SiMe3]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 sigma(3)lambda(3)-phosphiranes 15a-o. Investigations performed between 30 and 180-degrees-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,l 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.