Rationalizing the Effect of Ligand Substitution Patterns on Coordination and Reactivity of Alkali Metal Aminotroponiminates

A small series of
alkali metal aminotroponiminates (ATIs), [M­(ATIPh/Ph)­(thf)n], have been
synthesized and fully characterized (M = Li, Na, K). All of these
compounds adopt coordination modes that differ from those reported
for derivatives with a slightly varied substitution pattern at the
ATI ligand (one or two of the N-bound Ph groups substituted by iPr groups). This leads to an unprecedented ATI coordination
mode for the potassium compound [K­(ATIPh/​Ph)] and an unusual Li···Ph interaction for the lithium
compound [Li­(ATIPh/​Ph)]. The influence of
the substitution pattern at the ATI ligand on the shape and energy
of the frontier orbitals of its sodium complexes has been rationalized
by theoretical methods and correlated with experimental results. Analytical
techniques applied in this work include NMR spectroscopy, single crystal
X-ray diffraction, and DFT calculations.