Steps toward the synthesis of a geodesic C 60 H 12 end cap for a C 3v carbon [6,6]nanotube Thomas J. Hill, Richard K. Hughes, Lawrence T. Scott * Department of Chemistry, Merkert Chemistry Center, Boston College, 2609 Beacon Street, Chestnut Hill, MA 02467-3860, USA article info Article history: Received 16 July 2008 Received in revised form 22 September 2008 Accepted 26 September 2008 Available online 8 October 2008 Dedicated to Professor Reginald H. Mitchell on the occasion of his 65th birthday abstract Several shape-persistent carbon-rich nanomolecules with diameters exceeding 1.7 nm have been pre- pared by the aldol trimerization of 20-carbon aromatic ketones bearing chlorine atoms at various sites. These C 60 H 27 Cl 3 and C 60 H 24 Cl 6 polycyclic aromatic compounds represent attractive intermediates for the synthesis of a geodesic C 60 H 12 end cap of a C 3v carbon [6,6]nanotube. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Carbon nanotubes have been widely touted for their potential to fulfill dreams in materials science and in the emerging realm of nanotechnology. 1–4 They also hold considerable intrinsic scientific interest owing to their unusual curved networks of trigonal carbon atoms. Despite intense scrutiny by scientists and engineers worldwide for nearly two decades, however, these fascinating carbon-rich materials are still being made today by poorly un- derstood empirical methods. 5–8 We contend that such targets should be accessible by rational chemical synthesis and that the successful realization of the requisite synthetic methods will revolutionize the science of carbon-rich materials. Our 12-step laboratory synthesis of fullerene-C 60 by chemical methods in 2002 9–11 represents one milestone in the journey toward that goal. In recent years, we have begun to focus our research on the development of chemical methods for the rational, structure-spe- cific synthesis of single-chirality, all-carbon, single walled nanotubes (SWNTs). The structural variety possible for carbon nanotubes is virtually limitless. 3,12,13 They come in all different dia- meters. The orientation of the benzene rings along the shaft can be chiral (helical) or achiral, and the chiral tubes vary according to the pitch of the helix. Achiral tubes are classified according to the ap- pearance of their rims as either ‘zig-zag’ or ‘armchair’. Both ends can be open, or both can be closed, or a single tube may have one end of each type. Superimposed on all of that, carbon nanotubes can be single walled, double walled, or multiwalled, with more than 10 coaxial tubes nested together. 3,12,13 Carbon nanotubes from all of these classes are already known, and their properties vary as a function of structure. 3,12,13 Unfortunately, empirical methods 5–8 do not produce homogeneous samples in which all the carbon nanotubes have the same predefined diameter and chirality (ring orientation). The problem is compounded by the fact that, unlike the fullerenes, carbon nanotubes made in this way cannot be sep- arated and purified to homogeneity by chromatographic methods, because they are totally insoluble. 14,15 This problem represents a clear challenge to synthetic organic chemists! Where should one begin? We have chosen the achiral, armchair, all-carbon, single walled nanotubes (e.g., [6,6]SWNTs) as our highest priority targets. Such nanotubes are expected to exhibit metal-like behavior, regardless of diameter. 1,3,12,13 Consequently, they all hold the potential to find use as ultra-thin, super-strong, electrically conducting nanowires in myriad nanoelectronic de- vices. Most zig-zag tubes and chiral tubes, by contrast, are expected not to exhibit metal-like behavior. 1,3,12,13 The choice of initial targets thus seems obvious to us. This paper describes one approach to the chemical synthesis of [6,6]SWNTs. 1.1. General strategy The course we are pursuing builds on our previous experience with syntheses of open geodesic polyarenes. 11,16,17,18 Figure 1 il- lustrates the general strategy, as applied to a proposed synthesis of [6,6]SWNTs that are closed at one end and open at the other. As we see it, two major hurdles must be surmounted to produce SWNTs by this general strategy: (1) synthesis of a geodesic polyarene that has the initial armchair rim and six fully unsaturated five-mem- bered rings, as required for a hemisphere by Euler’s theorem 19 and * Corresponding author. Tel.: þ1 617 552 8024; fax: þ1 617 552 6454. E-mail address: lawrence.scott@bc.edu (L.T. Scott). Contents lists available at ScienceDirect Tetrahedron journal homepage: www.elsevier.com/locate/tet 0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2008.09.087 Tetrahedron 64 (2008) 11360–11369