Molecular belts

01 August 2009 - Part II

Two succesfull attempts have been reported recently synthesising a new class of molecular belts, the so-called cycloparaphenylenes (carbon nanohoops in marketing speak) that are taking cyclophanes one step further. Jasti & Bertozzi et al. (DOI) beat Takaba & Itami et al. (DOI) by a good five months. The cycloparaphenylene molecule (C6H4)12 in question consists of 12 phenylene units linked together by para joints. It can be envisioned as cyclic poly(p-phenylene) and also as a carbon nanotube segment. Both methods rely at some point on a Suzuki reaction. In the Bertozzi method several oligomers have to be separated:

Not so in the Itami method:

Key strategic advantage for both: direct cyclization of phenylene units would increase ring strain by 50 kcal/mole (will fail) whereas same step with intermediates containing unsaturated rings adds only 5 kcal/mole strain.

Also see molecular belts part I