Synthesis of substituted polycyclooctatetraenes

A detailed account of the synthesis of Shirakawa polyacetylene may be found in [152]. 10.4.1 Synthesis of Substituted Polycyclooctatetraenes 

The metathesis catalysts, W CH(terr-Bu))(iV-(2,6-(i-Pr)2CjH3)(OCMe(CF3)2)2, 1 [153], and W(CH(o-MeOPh))(NPh)(OCMe(CF3)2)2 THF, 2 [91], were prepared using literature methods. Polymerizations and subsequent handling of polymer films and preparation of polymer solutions were conducted in a nitrogen-niled Vacuum Atmospheres drybox. In a typical polymerization, 2-3 mg of catalyst (1 or 2) was weighed into a vial and dissolved in a minimum of pentane (2-3 drops). One drop of THF was added to catalyst 1 to slow the rate of polymerization. Lewis bases will reversibly bind to the catalyst, slowing the rate of propaga- 

Isomerization of the polymer from a predominantly cis configuration to a predominantly trans configuration could be accomplished either thermally or photochemically. Thermal isomerization was accomplished by heating the sample in benzene or THF at 60-80°C in a tube sealed with a Teflon Kontes screw-top until the visible absorption spectrum showed no change. Photochemical isomerization was accomplished at 0°C (monitored by thermocouple and external meter in the bath) by exposure of the sample dissolved in THF or benzene to light from a Pyrex-filtered, 350 W, medium-pressure mercury Hanovia lamp (approximately 6-12 h for a sample concentration of 1 mg mL ). Overexposure resulted in a decrease in color indicating decomposition of the material in solution. THF, toluene and benzene were suitable solvents for this experiment. Chlorinated solvents sometimes lead to photobleaching. 

---