Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
J Am Chem Soc. 2013 Apr 24;135(16):6192-9. doi: 10.1021/ja400367h. Epub 2013 Apr 12.
Hydroxy group-selective acylation in the presence of more nucleophilic amines was achieved using acetates of first-row late transition metals, such as Mn, Fe, Co, Cu, and Zn. Among them, cobalt(II) acetate was the best catalyst in terms of reactivity and selectivity. The combination of an octanuclear cobalt carboxylate cluster [Co4(OCOR)6O]2 (2a: R = CF3, 2b: R = CH3, 2c: R = (t)Bu) with nitrogen-containing ligands, such as 2,2'-bipyridine, provided an efficient catalytic system for transesterification, in which an alkoxide-bridged dinuclear complex, Co2(OCO(t)Bu)2(bpy)2(μ2-OCH2-C6H4-4-CH3)2 (10), was successfully isolated as a key intermediate. Kinetic studies and density functional theory calculations revealed Michaelis-Menten behavior of the complex 10 through an ordered ternary complex mechanism similar to dinuclear metallo-enzymes, suggesting the formation of alkoxides followed by coordination of the ester.
在更具亲核性的胺存在下，使用第一过渡系列的 late transition metals 的醋酸盐，如 Mn、Fe、Co、Cu 和 Zn，可以实现羟基的选择性酰化。其中，二价钴醋酸盐在反应性和选择性方面是最好的催化剂。具有含氮配体的八核钴羧酸酯簇[Co4(OCOR)6O]2（2a：R = CF3，2b：R = CH3，2c：R = (t)Bu）与氮，如 2,2'-联吡啶，提供了用于 transesterification 的高效催化体系，其中成功分离出桥连双金属配合物 Co2(OCO(t)Bu)2(bpy)2(μ2-OCH2-C6H4-4-CH3)2（10）作为关键中间体。动力学研究和密度泛函理论计算表明，配合物 10 通过类似于双核金属酶的有序三元复合物机制表现出 Michaelis-Menten 行为，表明烷氧基的形成随后是酯的配位。
