The oxidative coupling reaction can efficiently be promoted by supported ruthenium catalyst Ru(OH)x/Al2O3. A variety of 2-naphthols and substituted phenols can be converted to the corresponding biaryl compds. in moderate to excellent yields using mol. oxygen as a sole oxidant in water without any additives. The catalysis is truly heterogeneous in nature, and Ru(OH)x/Al2O3 can easily be recovered after the reaction. The catalyst can be recycled seven times with the maintenance of the catalytic performance, and the total turnover no. reaches up to 160. The results of competitive coupling reactions suggest that the present oxidative biaryl coupling reaction proceeds via the homolytic coupling of two radical species and the Ru(OH)x/Al2O3 catalyst acts as an one-electron oxidant. Two radical species are coupled to give the corresponding biaryl product, and the one-electron reduced catalyst is reoxidized by mol. oxygen. The amts. of O2 uptake and H2O formation were almost one-quarter and one-half the amt. of substrate consumed, resp., supporting the reaction mechanism. The kinetic data and kinetic isotope effect show that the reoxidn. of the reduced catalyst is the rate-limiting step for the coupling reaction. [on SciFinder(R)]
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