EDA Complexes of N-halosaccharins with N- and O-donor ligands

Abstract

A series of EDA complexes of N-iodosaccharin (NISac) and N-bromosaccharin (NBSac) with nitrogen and oxygen electron-pair donors, NISacÁH 2 O, NISacÁTHF, NISacÁPy, NISac 2 ÁPyz and NBSac 2 ÁPyz, was prepared and examined by X-ray diffraction and NMR. The complexes are relatively stable, crystalline compounds with the ligand bound to the halogen atom in a nearly linear arrangement N-halogen-ligand. The halogen-ligand distances are inversely proportional to the donor ability of the ligand. The interactions between ligand and halogen are stronger for iodine than bromine. The X-ray structure analysis has shown that for some compounds the N-X bond in the halosaccharin moiety is not coplanar with the isothiazole ring, and the quantum-chemical calculations demonstrate a high flexibility of the corresponding angle. Complexes were modelled also by DFT calculations using B3LYP and MPW1K functionals. A better fit of the computed geometry was obtained by the geometry optimization in a polar solvent continuum than in vacuum.

Alternative Motifs for Halogen Bonding

“…N ‐Halosaccharins, namely N ‐iodosaccharin (NISac) and N ‐bromosaccharin (NBSac), represent another group of potent XB donors that form very strong and close‐to‐linear halogen bonds with N‐ and O‐containing ligands. Dolenc and Modec54 reported the crystal structures of NISac · H 2 O (MUGCOH), NISac · THF (MUGCUN), NISac · pyridine (MUGDAU), (NISac) 2 · pyrazine (MUGDEY) and (NBSac) 2 · pyrazine (MUGDIC). Interestingly, the water molecule in NISac · H 2 O forms a strong N–I ··· O halogen bond with the iodine atom but also two O–H ··· O hydrogen bonds with the carbonyl and sulfone group.…”

NX⋯Y halogen bonds. Comparison with NH⋯Y H-bonds and CX⋯Y halogen bonds

“…Even shorter distances are observed when the XB acceptor is an anion, 41 an amine or triazine, 45,46 or an imine. 49 A very recent study 50 paired halosaccharins with a series of pyridine-N-oxides. 49 A very recent study 50 paired halosaccharins with a series of pyridine-N-oxides.…”

“…[41][42][43][44][45][46][47][48][49][50] As described below, a wide range of electron donor molecules is considered, including both lone pair and p-donors, and molecules of varying donor ability. We take as a starting point systems where there is available a significant amount of experimental data to serve as a check on the validity of the calculations.…”

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

“…The (imide)N⋅⋅⋅O(PyNO) distances, on the other hand, vary within a narrow range, 4.434(2)–4.481(2) Å for NISac‐ Z, and 4.163(2)–4.250(4) Å for NBSac‐ Z complexes, implying that only the donor halogen position is altered between N atoms and O atoms. The (imide)N⋅⋅⋅O(PyNO) distances of, NISac‐ Z are about 0.100 Å shorter than (imide)N⋅⋅⋅N(py) of NISac‐N py and, NBSac‐ Z are about 0.07 Å shorter when compared to (imide)N⋅⋅⋅N(py) of NBSac‐N py complexes . These findings suggest that the donor halogens of N‐halosaccharins are highly sensitive towards the electron density of the acceptor atoms, which is evidently larger for O‐atom of aromatic N ‐oxides.…”

“… Computed electrostatic potentials projected on the 0.001 au electron density surfaces of NISac, pyridine (py) and 1 , and crystal structures of NISac‐py and NISac‐ 1 .…”