Strong N−X⋅⋅⋅O−N Halogen Bonds: A Comprehensive Study on N‐Halosaccharin Pyridine N‐Oxide Complexes

Abstract

A study of the strong N−X⋅⋅⋅−O−N+ (X=I, Br) halogen bonding interactions reports 2×27 donor×acceptor complexes of N‐halosaccharins and pyridine N‐oxides (PyNO). DFT calculations were used to investigate the X⋅⋅⋅O halogen bond (XB) interaction energies in 54 complexes. A simplified computationally fast electrostatic model was developed for predicting the X⋅⋅⋅O XBs. The XB interaction energies vary from −47.5 to −120.3 kJ mol−1; the strongest N−I⋅⋅⋅−O−N+ XBs approaching those of 3‐center‐4‐electron [N−I−N]+ halogen‐bonded systems (ca. 160 kJ mol−1). 1H NMR association constants (KXB) determined in CDCl3 and [D6]acetone vary from 2.0×100 to >108 m−1 and correlate well with the calculated donor×acceptor complexation enthalpies found between −38.4 and −77.5 kJ mol−1. In X‐ray crystal structures, the N‐iodosaccharin‐PyNO complexes manifest short interaction ratios (RXB) between 0.65–0.67 for the N−I⋅⋅⋅−O−N+ halogen bond.

Halogen Complexes of Anionic N‐Heterocyclic Carbenes

“…For the solvate complexes, the enthalpies range from −5.7 kcal mol −1 for L=CH 3 CN to −10.8 kcal mol −1 for L=THF, which is typical, but at the stronger end for noncovalent halogen bonding [15, 16, 51, 52] . A significantly stronger interaction is calculated for the trimethylamine N ‐oxide adduct with Δ H 298K =−17.5 kcal mol −1 , which is on the same order of magnitude as that calculated for N ‐iodosaccharin pyridine N ‐oxide complexes [53] . Complexation of 2 a with the carbenes IDipp and IMes turned out to be more exothermic (Table 3), revealing a significantly higher stability of 2 a⋅ IDipp ( 5 a , −34.5 kcal mol −1 ) and 2 a⋅ IMes ( 5 b , −33.2 kcal mol −1 ).…”

Halogen Bond of Halonium Ions: Benchmarking DFT Methods for the Description of NMR Chemical Shifts

“… 4 The halonium ion of such three-center bonds simultaneously interacts with two Lewis bases with comparable bond strengths and lengths. 3 Strong, three-center halogen bonds of halonium ions with nitrogen, 5 − 14 oxygen, 15 sulphur, 16 − 18 selenium, 19 , 20 tellurium, 21 halogen, 22 and mixed nitrogen and oxygen 23 , 24 electron donors have lately received ample attention and also found applications in supramolecular chemistry, for example. 3 , 18 , 25 − 29 Although the halogen bond of neutral organic halogen bond donors, such as of iodoperfluorocarbons, is weak (<10 kJ/mol), 30 those of halonium ions are typically >50 kJ/mol and often even >100 kJ/mol.…”

O–I–O halogen bond of halonium ions

“…The energy range of halogen bonds overlaps with that of hydrogen bonds, 18 with the 3c4e halogen bonds being among the strongest secondary interactions (up to 120 kJ mol À1 ). 17 In addition to the 3c4e bonds 19 in trihalide anions, 20 3c4e halogen bond complexes have previously been formed using nitrogen, [21][22][23] sulphur, [24][25][26] selenium, 27,28 tellurium, 29 and mixed nitrogen and oxygen electron donors [30][31][32] (Fig. S1, ESI †).…”