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Issue 15, 2012
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Conformational analysis via calculations and NMR spectroscopy for isomers of the mono(imino)pyridineligand, 2-{(2,6-Me2-C6H3)NC(i-Pr)}C5H4N

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Abstract

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 in solution. Interconversion of these two isomers was verified by 2D-EXSY NMR spectroscopy. Calculations at the B3LYP and MP2 levels of theory reveal four relevant isomers, with two atropisomers of E geometry (1-EA and 1-EB) and two atropisomers of Z geometry (1-ZA and 1-ZB). A simple carbon–carbon bond rotation to alter the orientation of the isopropyl group provides a fifth, related conformer, 1-ZB, that is the most stable species at the MP2 level. The transition states for E/Z isomerization and the isomerization pathways between atropisomers have been characterized. Comparison of experimental and ab initio NMR chemical shifts in combination with NOE analysis suggests that isomers 1-EB and 1-ZB/1-ZB are the dominant species in our solution phase NMR studies. Our understanding of the isomerization behavior of 1 will help inform the future design of readily complexed, sterically hindered mono(imine) and bis(imine) ligands.

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

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Supplementary files

Article information


Submitted
17 Apr 2012
Accepted
01 May 2012
First published
02 May 2012

RSC Adv., 2012,2, 6237-6244
Article type
Paper

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

T. J. Dudley, J. E. Beck, E. E. P. Santos, K. A. Johnston, W. S. Kassel, W. G. Dougherty, W. J. Boyko and D. L. Zubris, RSC Adv., 2012, 2, 6237
DOI: 10.1039/C2RA20688A

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