Anion Rearrangements of Alkali Metal Complexes of the Chiral Amine (S)‑N‑α-(Methylbenzyl)phenylallylamine: Structural and Solution Insights

Reaction of the chiral amine (S)-N-α-(methylbenzyl)­phenylallylamine, [(S)-N-α-mbpa], with nBuM (M = Li, Na, K) in the presence of the Lewis donors TMEDA or THF (TMEDA = N,N,N′,N′-tetramethylethylenediamine, THF = tetrahydrofuran) resulted in a series of mono- or dimetalated complexes, [{PhC­(H)­CH3NC­(H)­C­(H)­C­(H)­PhLi2(TMEDA)2] 1, [{PhC­(H)­CH3NCHCHCH2PhNa­(TMEDA)]2 2, and [PhC­(CH2)­N­(CH2CH2CH3)­K]∞ 3, being formed with various 1,3-sigmatropic rearranged allylic bonding patterns. Completing previous work on the related amine N-α-(methylbenzyl)­allylamine, the potassiated aza-enolate complex [(R)-{(PhC­(CH2)­N­(CH2CH2CH3(THF)]∞ 4 is also reported. All four complexes 1–4 have been characterized by single-crystal X-ray diffraction and solution NMR spectroscopy studies. DTF calculations on model systems investigated the preference for the monomeric Li2-mbpa 1 to undergo isomerization to the aza-allyl anion conformation, which, interestingly, is more energetically stable as a monomeric complex.