THE SYNTHESIS, CHARACTERIZATION AND SOME PROPERTIES OF NEW QUASI-AROMATIC MAIN GROUP-RING SYSTEMS

The synthesis and characterization of several previously unknown ring systems that involve heavier main group elements are described. Four new types of potentially delocalized six-membered ring compounds that comprise the cyclic arrays (RBPR')3, (RAINR')3, (RZnSR')3 and (GeNR')3, are considered. The synthetic routes to these rings are straightforward and require only one or two steps to give the respective products in good yield. All the rings have been structurally characterized. The structures, in conjunction with spectroscopic data, indicate considerable variation in delocalization with ring type. Quasi-aromaticity in the case of the (RBPR')3 ring is well supported by the experimental data and, indirectly, by the non-planar structure that was observed for the 'anti-aromatic' four-membered (RBPR')2 rings. Further support comes from recent calculations at the SCF level using the basis set 6-31G* which indicate that the (HBPH)3 system has a similar stabilization to that seen in borazine, whereas the (HAlNH)3 ring exhibits only a minor degree of delocalization of the pi-electrons.