Unusual and unprecedented rings and cages derived from main group elements

This research account presents our significant recent findings in the area of small cage main group metallacarboranes during the past several years. The highlights of these findings are as following: (1) The reactivity study on the carbons apart C4B8-carborane led to the introduction of an unusual carborane species that acts as a restricted electron-acceptor by removing only the valence electrons of a group 1 or group 2 metal, thus forming the corresponding alkali and alkaline earth metal compounds. Further reactivity study of these species in solvent extraction of radioactive cesium metal ion (Cs-137(+)) from nuclear wastes has rekindled our interest to explore new avenues in this area of main group metallacarborane research. (2) The syntheses and structures of main group metallacarboranes have exemplified their rich structural and coordination chemistry beyond their existence as versatile synthons for the production of other metallacarboranes of d- and f-block elements. (3) Synthesis and reactivity study on half- and full-sandwich gallacarboranes opened up the possibility of using such compounds as precursors in the formation of conducting materials. (4) Even though two germanium atoms are present formally in +2 and +4 oxidation states, the reactivity study on the mixed-valence digermacarboranes with Lewis bases shows no indication of exo-polyhedral Ge(IV) atom being the Lewis acid site. And finally, (5) our research has demonstrated that the 'electron-deficient' cages can be quantitatively transformed into the corresponding 'electron-precise' heterocyclic rings.