Conformational analysis via calculations and NMR spectroscopy for isomers of the mono(imino)pyridine ligand, 2-{(2,6-Me2-C6H3)NC(i-Pr)}C5H4N

• DOI: 10.1039/c2ra20688a
• Publication Date: 2012-05-02T10:30:53Z
• Authors: Timothy J. Dudley; Jennifer E. Beck; Earl E. P. Santos; Kathryn A. Johnston; William S. Kassel; William G. Dougherty; Walter J. Boyko; Deanna L. Zubris
• Keywords: Atropisomer; Imine; Conformational isomerism; Isopropyl

Sterically hindered (imino)pyridine 2-{(2,6-Me2-C6H3)NC(i-Pr)}C5H4N (1) was synthesized via addition of isolated imidoyl chloride to an in situ lithiated pyridine. Room temperature 1-D and 2-D NMR spectroscopy reveals two rapidly equilibrating isomers solution. Interconversion these verified by 2D-EXSY spectroscopy. Calculations at the B3LYP MP2 levels theory reveal four relevant isomers, with atropisomers E geometry (1-EA 1-EB) Z (1-ZA 1-ZB). A simple carbon–carbon bond rotation alter orientation isopropyl group provides a fifth, related conformer, 1-ZB′, that is most stable species level. The transition states for E/Z isomerization pathways between have been characterized. Comparison experimental ab initio chemical shifts combination NOE analysis suggests 1-EB 1-ZB/1-ZB′ are dominant our solution phase studies. Our understanding behavior 1 will help inform future design readily complexed, sterically mono(imine) bis(imine) ligands.