Salicylaldimines: Formation via Ring Contraction and Synthesis of Mono- and Heterobimetallic Alkali Metal Heterocubanes

The formation of salicylaldimine
derivatives via ring contraction
as byproducts in 2-aminotropone syntheses has been investigated. Salicylaldiminate
(SAI) complexes of the alkali metals Li–K have been synthesized
and transformed into heterobimetallic complexes. Important findings
include an unusual double heterocubane structure of the homometallic
sodium SAI, an unprecedented ligand-induced E/Z isomerization of the aldimine functional group in the
homometallic potassium SAI, and the first example of a structurally
authenticated mixed-metal SAI based on s-block central atoms. Rapid
equilibria have been shown to play a crucial role in the solution
phase chemistry of mixed-metal SAIs. Analytical techniques applied
in this work include (heteronuclear) NMR spectroscopy, VT- and DOSY
NMR spectroscopy, high-resolution mass spectrometry, single-crystal
X-ray diffraction analysis, and DFT calculations.