Novel Conjugated Polymer Containing Aromatic Ring and Selenium in Backbone. Kinetics of Substituent Effect on the Addition Reaction of Benzeneselenols to Ethynylbenzenes as a Model for Addition Polymerization

Abstract

Substituent effect on the addition reaction of benzeneselenols to ethynylbenzenes was investigated as a model for addition polymerization to give conjugated polymer containing aromatic ring and selenium atom in the backbone. The addition reaction of benzeneselenols to ethynylbenzenes having p-methoxy, p-methyl, p-chloro, and p-H substituent groups occurred readily without appreciable side reactions. Adducts of the anti-Markownikoff’s structure were obtained in >99% yield. Relative reactivity of the addition step of the benzeneseleno radical to substituted ethynylbenzenes, which is the rate-determining step, was found to decrease in the order of p-methoxy, p-methyl, p-chloro, and p-H. Relative reactivity of substituted benzeneseleno radicals to ethynylbenzene, on the contrary, increased in the above order. These relative reactivities were better correlated by the modified Hammett’s equation containing a resonance effect than by the simple Hammett’s equation. These results indicate that a perturbation between SOMO of benzeneseleno radical and HOMO of ethynylbenzene in the transition state is an important controlling factor for the addition reaction. The substituent effect of the chain transfer step between β-phenylselenostyrylene radical (⌬–Ċ=CH–Se–⌬) and p-Y benzeneselenols was also determined. The experimental data were compared with the energy levels of HOMO, SOMO, and LUMO calculated by CAChe system (PM3). The results were also compared with those of the addition reactions of benzenethiol to ethynylbenzene and benzeneselenol to styrene. The transition state of the addition reaction of benzeneselenol to ethynylbenzene was found to be similar to that of benzenethiol to ethynylbenzene and benzeneselenol to styrene.