Toward the synthesis of a carbon nanotube end-cap

Abstract

The synthesis of carbon nanotubes is of great interest to a wide variety of chemists. Our approach uses traditional organic synthesis to build rationally designed fullerene fragments, which can be grown into carbon nanotubes. Two target bowls were selected for this research; one consisting of 50 carbon atoms, and the second containing 40. Both bowls, when grown through a repetitive sequence of Diels-Alder addition and rearomatization, would result in the formation of [5,5] carbon nanotubes. The first route attempted was the synthesis of a C50H10 end-cap using diphenanthrylcorannulene as an advanced intermediate. However, after a great deal of trial and error to make the substituted diphenanthrylketone needed, the route was abandoned when the aldol condensation of this ketone with acephenanthrylquinone could not be made efficient enough to continue with the synthesis. The second synthetic target, the C40H10 end-cap, was pursued through the synthesis of corannulene, which was then substituted with bromine. The bromine atoms were converted to vinyl groups, and a Diels-Alder cycloaddition followed by rearomatization forms the new benzo substituent. This was successful for the smallest members of the benzocorannulene family; however, the yields were too low for a practical route to pentabenzo[a,d,g,j,m]corannulene from corannulene, which was the planned precursor for the ultimate formation of the target bowl. An adapted method was employed for the synthesis of larger benzologs. Tribenzo[a,d,j]corannulene was prepared through a modified version of the literature method for the synthesis of dibenzo[a,g]corannulene. With this material characterized and available in gram quantities, the synthesis of pentabenzo[a,d,g,j,m]corannulene was pursued through the dibromination of tribenzo[a,d,j]corannulene, followed by vinylation and subsequent Diels-Alder reaction to accomplish a two-fold benzannulation. This molecule was synthesized and characterized here for the first time. Tetrabenzo[a,d,g,j]corannulene was also observed in some of the reactions, but was never isolated or characterized.