The carbon–phosphorus coupling in the C spectrum is consistent with deprotonation of the methyl group rather than loss of that group:Addition to the nitrile initially gives . An intramolecular proton transfer then converts the imidoyl anion into a conjugated lithiated enamide:The phosphorus–carbon bond is retained. The rearrangement is a hydrogen migration, not a migration of the phosphoryl group to nitrogen. Addition of half an equivalent of TMEDA per Li gives the hemisolvated dimerThe tetrameric and dimeric nuclearities are established for this reaction system; the spectra in the question are consistent with them, but spectra alone would not uniquely prove every detail of the aggregates.[ref]
Lithiated organophosphorus enamines: a new synthetic approach and the first crystal structures by William Clegg and others. Abstract and structures of the unsolvated enamide and its TMEDA hemisolvate, pages 1401–1402