he Synthetic Organic Chemistry Program is supporting the research of Dr. James C. Martin of the Department of Chemistry at Vanderbilt University. Dr. Martin is developing routes to an exciting class of molecules which contain one or more of a so-called hypervalent atoms that impart unique properties to the molecule. These will provide the new methods for the increasingly complex materials needed by agriculture, medicine and industry. An understanding of the charge distribution and preferred geometry for hypervalent main-group element species has allowed the development of several bidentate, tridentate, and tetradentate ligands to provide important effects on the chemical reactivity of these species. Important tridentate ligand species, with two apical fluoroalkoxy ligands connected by five-membered rings to an equatorial aryl carbon, are easily synthesized by reactions of main-group element species with a trilithio derivative prepared from the iodinane by reaction with n-butyllithium. The iodine(V) species, produced by oxidation of the iodinane with fluorine, followed by other reactions, are useful as oxidizing agents. A neutral selenium analogue with an equatorial methyl group is a very interesting methylating agent. Some of these compounds are expected to provide applications in materials science. The hexaiodobenzene dication, which was recently reported as a ten-electron sigma-delocalized aromatic species involving the in-plane p-orbitals of the six iodines, could be considered a species with a pentaiodophenyl tridentate ligand attached to a six-electron iodine dication. The sigma-delocalized aromatic system provides stabilization for this tridentate ligand. Introduction of other 6-electron centers, such as carbocations, to the pentaiodophenyl ligand has been effected and the possibility of sigma-delocalized stabilization will be studied. Analogues with iodines replaced by other main-group elements of similar van der Waal's radii are expected to provide comparable sigma-delocalized aromatics, not only for hexasubstituted benzenes, but also for naphthalene and other pi-aromatic centers, as well as some alkyl centers with arrangements of the main group atoms in cyclic array with close arrangement of the atoms relative to neighboring atoms. Hexakis-(selenophenyl)benzene dication has been made, with evidence for sigma-delocalized aromaticity. Several other aromatic species, with a tree-center four-electron hypervalent bond parallel to the p-orbitals of a pi-aromatic system, species which are called bis-ipso aromatic species, have been prepared. These provide stabilization for hypervalent boron or carbon species, and possibly even nitrogen species. Aluminum analogues of the hypervalent boron species, reported earlier, have been prepared for comparisons. A wide range of elements are to be studied in related aromatic species.
