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

Abstract

In this systematic study six new chiral alkali-metal complexes derived from (S)-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 (3) when using nBuLi or the aza-allyl complexes [Na{PhC(Me)NCHPh}·TMEDA]∞ (4), [Na{PhC(Me)NCHPh}·3THF] (5), [Na{PhC(Me)NCHPh}·THF·TMEDA] (6), and [K{PhC(Me)NCHPh}·PMDETA]∞ (8) 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 nBuNa or nBuK to give the unexpected 1, 3-diphenyl-2-aza-allyl complexes[M{(PhCH)2N}·L] [M = Na, L = 3 THF (5a) or TMEDA/THF (6a); M = K, L = PMDETA (8a)] 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 CH4.