Diphosphaallyl cations

The phosphonium phosphaalkenes are formed via the diphosphaallyl cation after the cationic rupture of an extracyclic C—Cl bond. Contrary to the photochemical or anionic ring-opening reactions, the cationic intermediates are not detected. The theoretical calculations performed on unsubstituted derivatives reveal for this reaction a P—P bond rupture by a disrotatory process leading directly to an exo-exo open chain structure <92IC2414>. 

AgOTf or Gads followed by a [3 + 2] cycloaddition of the intermediate diphosphaallylic cation with acetonitrile as dipolarophile. Compounds 126 were then deprotonated with LiHMDS to give the stable PHC 127. 

Recently, detailed P NMR studies of the formation of the 1,2-diphosphaallyl anion were carried out in order to increase its unacceptably low yield. This led to the very surprising discovery that an unstable ElZ- (5 P-Si +41.4 5 P-C +454.2 ppm jpp 460.6 Hz) as well as the finally isolated EIE- sova.er (8 P-Si +8.0 8 P-C 411.1 ppm jpp 461.2 Hz l,2-dimethoxyethane/[D5]-benzene solution) are present in the reaction mixture. An X-ray structure determination shows the solid compound to be built up of discrete tris(l,2-dimethoxyethane-0,0 )lithium cations and / -isomeric 3-phenyl-l,3-bis(trimethylsilyl)-l,2-diphosphapropenide anions (Fig. 6). 

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