Catalysts for asymmetric‐induction polymerization of benzofuran. II. Properties and catalyses of some binary systems containing the menthoxy group

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Abstract
It has been found that the equimolar binary system consisting of aluminum trichloride and (−)‐menthoxytriethyltin, ‐germanium or ‐silicone is effective for the asymmetric‐induction polymerization of benzofuran in toluene at −78°C. The specific rotation [α]D of the resultant polybenzofuran ranged from +10° to +40°, depending on the polymerization conditions as well as the metal atoms constituting the menthoxy compounds. The 1:1 ethylaluminum dichloride—menthol system was also effective for the same polymerization. It was confirmed that these binary systems easily undergo an exchange reaction, giving a dimeric menthoxyaluminum dichloride, (Men*OAlCl2)2, m.p. 72–75°C. A toluene solution of the crystalline dimer polymerized benzofuran into a high polymer having as large an [α]D value as +79.4°, although polymerization with the dimer was much slower than that with the parent binary mixtures. All these results lead to the conclusion that the true catalytic species of our multicomponent systems is most probably the dimeric menthoxyaluminum dichloride.

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