Molecular Templates with Potential for the Selective Production of Single Walled Carbon Nanotubes

While carbon nanotubes hold tremendous promise as revolutionary materials for numerous applications, the full potential of this material category will not be realized until impurity free, topologically pure samples are available in industrially useful quantities.  In the case of any organic target, natural or unnatural, absolute structural and chiral purity is most commonly accessed through rational organic synthetic chemistry.  With these guidelines we set out to synthesize highly curved aromatic templates from which structurally and chirally pure SWCNTs can be grown.

[5,5] carbon nanotube precursors, pentaindenocorannulene and [5,5] nanotube end cap, were both synthesized in three steps from corannulene.  Symmetric five-fold chlorination of corannulene using iodine monochloride gave pentachlorocorannulene.  1,3,5,7,9-pentakis(o-chlorophenyl)corannulene was prepared from pentachlorocorannulene by Suzuki coupling with o-chlorophenylboronic acid.  Pentaindenocorannulene was then achieved by a microwave assisted five-fold aryl-Heck type transformation of 1,3,5,7,9-pentakis(o-chlorophenyl)corannulene.  Alternatively, 1,3,5,7,9-pentakis(2,6-dichlorophenyl)corannulene was accessible from pentachlorocorannulene by palladium mediated Negishi coupling with in situ prepared 2,6-dichorophenylzinc chloride.  The fully formed [5,5] end cap was realized by subjecting 1,3,5,7,9-pentakis(2,6-dichlorophenyl)corannulene to flash vacuum pyrolysis.  Mass analysis, NMR and crystal structure characterization of pentaindenocorannulene and the short, structurally pure [5,5] nanotube end cap have been obtained.

The two aforementioned targets, together with the relatively simple to obtain pentaphenylcorannulene, form a small but very interesting series of high potential [5,5] carbon nanotube precursors.  Efforts to completely dehydrogenate and subsequently elongate these materials on a metal surface into quantities of pure full length [5,5] nanotubes by chemical vapor deposition techniques are in progress by way of key collaborations.