Are lithium and sodium salts of N-(2-hydroxyphenyl)-salicylaldimine aromatic metalla-hetero[10]annulenes? An answer given by spatial magnetic properties (through space NMR shieldings—TSNMRS)

Abstract

The spatial magnetic properties (through space NMR shieldings-TSNMRS) of the enol tautomer of N-(2-hydroxyphenyl)-salicylaldimine, the lithium and sodium salts in comparison with cyclodecapentaene and pyrano[2,3-b]pyrrole were studied to answer this question.

Ortho‐Quinone Methide Driven Synthesis of New O,N‐ or N,N‐Heterocycles

“…Specifications normally employed from magnetic point of view to quantify, e. g ., (anti)aromaticity, are theoretical non‐measurable items: single NICS values or components of the latter, or traces of NICS or components of the latter starting from the centre of the (anti)aromatic compound up to 10 Å outwards. Experimental Δδ/ppm in proton NMR spectra, in turn, are the molecular response property of our TS NMRS values . For this latter reason, the spatial magnetic properties (TS NMRS values) of 12 H ‐benzo[ a ]xanthen‐12‐one 11 (and, vide infra , of the preferred conformers/diastereomers of the new O , N ‐ and N , N ‐heterocycles) have been calculated and examined with respect to (i) the combined ring current effect of the C‐7a to 11a phenyl residues and the anisotropy effect of the carbonyl moiety on the chemical shift of H‐1 in 11 ( cf .…”

“…This is in no case remarkable. The experimental proton chemical shift δ( 1 H)/ppm is the molecular response property of the spatial magnetic properties TS NMRS ( e. g ., the anisotropy/ring current effect) . Both the chemical shift difference between the phenyl protons in the cis ( 17 a ) and the trans diastereomer ( 32 b ) [Δδ(H‐5′‐H‐4)=0.07 ppm, Δδ(H‐4′‐H‐3=−0.07 ppm] and the calculated ring current effects [Δδ(H‐5′‐H‐4)=‐0.34 ppm, Δδ(H‐4′‐H‐3=+0.02 ppm] are comparable.…”

Quantification and Visualization of the Anisotropy Effect in NMR Spectroscopy by Through-Space NMR Shieldings

“…In other complexes studied and where chelatoaromaticity was assumed (acetylacetonato chelato complexes, metallobenzenes complexes, orthohydroxy-para-pyrone chelato complexes and the molybdenum dithiolene complex 20a) [77] as well as in the corresponding free ligands chelatoaromaticity could not be identified [77]. Herefrom can be concluded that approving the lithium and sodium salts of N-(2-hydroxyphenyl)salicylaldimine as the first example of metalla-hetero [10]annulene goes too far [78] and when evaluating aromaticity [80,81], which is a multidimensional characteristic [81] dependent on energetic, geometric and magnetic criteria [82,83], that all items must be considered. Scheme 3.11), the magnetic criteria (spatial magnetic properties-TSNMRS) were studied in order to compare with previous results (cf.…”

“…36 Visualization of the magnetic properties (TSNMRS) of N-(2-hydroxyphenyl) salicylaldimine 21 (left) and 1,3-dihydroxy-naphthyl-2-aldehyde 24 as ICSS of different direction and size. Reproduced by permission of the PCCP Owner Societies[78].…”

NMR Spectroscopic Study of Tautomerism in Solution and in the Solid State

“…Employing the same methodology [38,39], the preferred quinoid type structure of a bridged bisphenazine type molecule 19 could be assigned [43] (Scheme 5.13). On the other hand, employing the same methodology again [38,39], the enol form and the lithium and sodium salts of N(-2-hydroxyphenyl)-salicylaldimine could be readily identified to be not the first example of metalla-hetero[10]annulenes [44].…”