N-Iodophthalimide as a halogen bond donor, a comparison with N-iodosuccinimide and N-iodosaccharin

We investigate here the ability of N-iodophthalimide (NIPht) to act as a halogen bond (HaB) donor, in comparison with well-known HaB donors N-iodosuccinimide (NISucc) and N-iodosaccharin (NISacc). The structure of NIPht itself is reported, together with those of neutral adducts with 4-dimethylaminopyridine (DMAP), 4,4 '-bipyridine and 2,2 '-bipyridine derivatives. Comparison with analogous adducts involving NISucc and NISacc shows that NIPht behaves essentially like NISucc as a HaB donor, both forming weaker adducts than NISacc with a given Lewis base. A symmetric anionic complex [NPht-I-NPht](-) is isolated in the presence of [K(18-crown-6)](+). It exhibits N-I distances very close to those observed in the known [NSucc-I-NSucc](-) and [NSacc-I-NSacc](-) species (2.24-2.26 & Aring;), confirming the 3-center-4-electron (3c-4e) character of the bonding in these species. This similarity confirms the peculiar character of the only other reported salt of [NPht-I-NPht](-), namely [Me4N][NPht-I-NPht], where the longer N-I distances (2.29 & Aring;) are a consequence of a specific solid-state arrangement and C-H & ctdot;O hydrogen bonds.