Unusual Solvent-Promoted Smiles Rearrangement of Two Different Phosphorus-Containing Organolithium Compounds to the Same Lithium Phosphide. Crystal Structure of MeP{C₆H₄-2-CH(C₆H₄-2-CH₂NMe₂)NMe₂}Li(THF)₂

Treatment of the tertiary phosphines RP(C₆H₄-2-CH₂NMe₂)₂ (R = Me, 1; R = i-Pr, 4) with n-BuLi in THF yields the lithium phosphides [RP{C₆H₄-2-CH(C₆H₄-2-CH₂NMe₂)NMe₂}]Li(THF)₂ (R = Me, 5; R = i-Pr, 6) as the sole phosphorus-containing products. Compound 5 is also obtained when either the lithium phosphinomethanide Li{CH₂P(C₆H₄-2-CH₂NMe₂)₂} (3) or the benzyllithium complex [MeP(C₆H₄-2-CH₂NMe₂){C₆H₄-2-CH(Li)NMe₂}]₂ (2) is dissolved in THF. Conversion of 2 to 5 is extremely rapid, whereas conversion of 3 to 5 takes several days at room temperature. The deuterium-labeled compound Li{CH₂P(C₆H₄-2-CD₂NMe₂)₂} (3a) isomerizes in THF to DCH₂P(C₆H₄-2-CD(C₆H₄-2-CD₂NMe₂)NMe₂}Li(THF)₂ (5a) and shows a strong kinetic isotope effect in comparison to the isomerization of 3. Compounds 5 and 6 have been characterized by multinuclear NMR spectroscopy and X-ray crystallography, and a mechanism for their formation from 1−4 is proposed.