Study of the D?Sb (D = O, S) Transannular Interaction in Sb-Monohalogenated Dibenzostibocines ? An Experimental and Theoretical Study

In order to gain a greater insight in the nature of the D?Sb transannular interaction in dibenzostibocines, a series of D(C6H4S)2SbHal complexes (D = S; Hal = Cl 1, Br 2, I 3; D = O, Hal = Cl 4) has been synthesised. X-ray structure determinations of complexes 1?4 reveal that the antimony atom is in a distorted ?-bipyramidal geometry, acting as an acceptor atom. The eight-membered ring conformation in 1, 2 and 4 can be described as a twist-boat, while in 3 it is approaching Cs symmetry. DFT calculations were carried out on 1 and 4. Topological analysis of the electron density in 1 and 4 showed the presence of critical points in the D?Sb direction (D = O, S). The electron localisation function showed the presence of a lone pair located in an equatorial position on the antimony, and a lone pair of the donor along the D?Sb direction, confirming the presence of a dative bond in the system. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)