Heterogeneously catalyzed aerobic oxidative biaryl coupling of 2-naphthols and substituted phenols in water
Heterogeneously catalyzed aerobic oxidative biaryl coupling of 2-naphthols and substituted phenols in water
复制标题
DOI：
10.1021/ja050436k
复制
发表时间：
2005-05-11
影响因子：
15
通讯作者：
Mizuno, N
中科院分区：
文献类型：
--
作者：
Matsushita, M;Kamata, K;Mizuno, N
负载型钌催化剂Ru（OH）（x）/Al_2O_3能有效地促进氧化偶联反应。使用分子氧作为唯一氧化剂，在不含任何添加剂的水中，多种2-萘酚和取代苯酚可以以中等至优异的产率转化为相应的联芳化合物。该催化剂在性质上是真正多相的，并且Ru（OH）（x）/Al 2 O3在反应后可以容易地回收。该催化剂可循环使用7次，总循环次数可达160次。竞争偶联反应的结果表明，本氧化联芳基偶联反应是通过两个自由基物种的均裂偶联和Ru（OH）（x）/Al 2 O3催化剂作为一个单电子氧化剂进行。两个自由基物种偶联得到相应的联芳基产物，并且单电子还原的催化剂被分子氧再氧化。O-2吸收量和H2O形成量分别为底物消耗量的近四分之一和一半，支持反应机理。动力学数据和动力学同位素效应表明，还原态催化剂的再氧化是偶联反应的限速步骤。
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 compounds in moderate to excellent yields using molecular 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 number 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 molecular oxygen. The amounts of O-2 uptake and H2O formation were almost one-quarter and one-half the amount of substrate consumed, respectively, supporting the reaction mechanism. The kinetic data and kinetic isotope effect show that the reoxidation of the reduced catalyst is the rate-limiting step for the coupling reaction.