Covalent and ionic bonding in bi- and tricyclic Group 15 amides: equidistant P-I and As-I bonds and fluxional cations.

A series of trivalent Group 15 bis(tert-butylamido)cyclodiphosph(iii)azane element bi- and tricycles of the formulae {[(tBuNP)2(tBuN)2]ElX}, El = P, As, Sb, Bi, where X = Ph, OPh, OtBu, N3, hexamethyldisilylamide (HMDS), OTf, was synthesized from the corresponding chlorides via salt elimination. The ensuing compounds were studied spectroscopically and X-ray crystallographically with a particular focus on the length of the El-X bond. While the Group 15 element to phenyl and HMDS were of normal lengths and completely covalent, those to azide appeared to be partly ionic.