Alkali-Metal-Induced C–C Bond Cleavage and CH₄ Elimination in the Amido → Aza-Allyl Transformation of the (<i>S</i>)‑<i>N</i>‑α-(Methylbenzyl)benzylamido Anion

In this systematic study six new chiral alkali-metal complexes derived from (<i>S</i>)-α-(methylbenzyl)­benzylamine (α-mmba) have been synthesized and characterized in the solution state, with five successfully analyzed by single-crystal X-ray diffraction. The reaction products observed are highly dependent on the choice of alkali metal and Lewis donor used, affording either the amido deprotonation complex [Li­{PhCH­(Me)­NCH₂Ph}·HMPA]₂ (<b>3</b>) when using nBuLi or the aza-allyl complexes [Na­{PhC­(Me)­NCHPh}·TMEDA]_∞ (<b>4</b>), [Na­{PhC­(Me)­NCHPh}·3THF] (<b>5</b>), [Na­{PhC­(Me)­NCHPh}·THF·TMEDA] (<b>6</b>), and [K­{PhC­(Me)­NCHPh}·PMDETA]_∞ (<b>8</b>) via hydrogen elimination reactions. Unexpectedly a co- secondary product is also obtained when tridentate or pseudo-tridentate donor ligands are used in the reaction of α-mbba with either <i>n</i>BuNa or <i>n</i>BuK to give the unexpected 1, 3-diphenyl-2-aza-allyl complexes­[M­{(PhCH)₂N}·L] [M = Na, L = 3 THF (<b>5a</b>) or TMEDA/THF (<b>6a</b>); M = K, L = PMDETA (<b>8a</b>)] in various ratios. Reinforcing the experimental findings, formation of the methane elimination complex was confirmed via GC-headspace analysis experiments, while theoretical DTF calculations on model systems reinforce the experimental findings showing that thermodynamic gas elimination pathways trend toward the larger alkali metals with H₂ elimination kinetically favored over CH<sub>4