Professor YAMAGO, Shigeru and his research group “Development of New Synthetic Route to Hoop-Shaped π Conjugated Molecules” (Published in ” Angewandte Chemie Ineternational Edition”, 18 January 2010)

Professor YAMAGO, Shigeru and his research group

(Laboratory of Polymer Controlled Synthesis,Division of Materials Chemistry)


“Development of New Synthetic Route to Hoop-Shaped π Conjugated Molecules”


Published in ” Angewandte Chemie Ineternational Edition,” 18 January 2010

and Mr IWAMOTO T (from left)

Cycloparaphenylenes are hoop-shaped π conjugated molecules consisting from p-disubstituted benzene rings, and are the simplest structural unit of armchair carbon nanotubes. Due to their unique structure associated with expected unique properties, they have attracted the attention of various disciplines ranging from basic chemistry to material science. However, although they have a simple structure, their synthesis has been a significant challenge.

Figure 1. Chemical structure of single walled carbon nanotube. Cycloparaphenylene unit is highlighted as green color.

We envisioned that square-shaped tetra(para-substituted oligoaryl)platinum complex could be used as a universal precursor for cycloparaphenylenes. If multiple reductive eliminations of platinum from the complex occur, cycloparaphenylene could be formed. Based on this idea, we first treated 4,4′-bis(trimethylstannyl)biphenyl with one equivalent of  Pt(II) complex. The reaction occurred smoothly and we obtained the desired tetranuclear platinum complex in 57% yield. Bromine-induced reductive elimination of the complex also proceeded smoothly and gave [8]cycloparaphenylene in 45% yield. It is remarkable that [8]cycloparaphenylene was synthesized in high overall yield (25%) despite of the considerable high its strain energy of 74 kcal/mol. [8]Cycloparaphenylene emits yellow green fluorescent light upon UV irradiation. This compound and its analogues would be of interests as photonic and electronic materials.

Scheme 1. Synthesis of [8]cycloparaphenylene

The results were published in Angewandte Chemie International Edition as a VIP (very important paper) article on January 18, 2010. The contents were also highlighted as an inside cover.

π conjugated molecule
π conjugated molecule is a molecule having alternating double and single bonds. Conductive polymers are part of π conjugated molecules.

Strain energy
Strain energy is a destabilizing energy of a molecule caused by the deviation of bond angle and/or bond length from the ideal structure.