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.