Solid-State and Solution Structures of Glycinimine-Derived Lithium Enolates

A combination of crystallographic, spectroscopic, and computational studies was applied to study the structures of lithium enolates derived from glycinimines of benzophenone and (+)-camphor. The solvents examined included toluene and toluene containing various concentrations of tetrahydrofuran, N,N,N′,N′-tetra­methyl­ethylene­diamine (TMEDA), (R,R)-N,N,N′,N′-tetra­methyl­cyclo­hexane­diamine [(R,R)-TMCDA], and (S,S)-N,N,N′,N′-tetra­methyl­cyclo­hexane­diamine [(S,S)-TMCDA]. Crystal structures show chelated monomers, symmetric disolvated dimers, S4-symmetric tetramers, and both S6- and D3d-symmetric hexamers. 6Li NMR spectroscopic studies in conjunction with the method of continuous variations show how these species distribute in solution. Density functional theory computations offer insights into experimentally elusive details.