de Boer Johannes W, Alsters Paul L, Meetsma Auke, Hage Ronald, Browne Wesley R, Feringa Ben L
Stratingh Institute for Chemistry, Faculty of Mathematics and Natural Sciences, University of Groningen, Nijenborgh 4, 9747, AG, Groningen, The Netherlands.
Dalton Trans. 2008 Nov 28(44):6283-95. doi: 10.1039/b809177c. Epub 2008 Oct 10.
The role played by the additives salicylic acid, L-ascorbic acid and oxalic acid in promoting the catalytic activity of MnIV2(O)3(tmtacn)22 (1(PF6)2, where tmtacn = N,N',N''-trimethyl-1,4,7-triazacyclononane) in the epoxidation and cis-dihydroxylation of alkenes with H2O2 and in suppressing the catalysed decomposition of H2O2 is examined. Whereas aliphatic and aromatic carboxylic acids effect enhancement of the catalytic activity of 1 through the in situ formation dinuclear carboxylato bridged complexes of the type [MnIII2(mu-O)(mu-RCO2)2(tmtacn)2]2+, for L-ascorbic acid and oxalic acid notable differences in reactivity are observed. Although for L-ascorbic acid key differences in the spectroscopic properties of the reaction mixtures are observed compared with carboxylic acids, the involvement of carboxylic acids formed in situ is apparent. For oxalic acid the situation is more complex with two distinct catalyst systems in operation; the first, which engages in epoxidation only, is dominant until the oxalic acid additive is consumed completely at which point carboxylic acids formed in situ take on the role of additives to form a second distinct catalyst system, i.e. that which was observed for alkyl and aromatic carboxylic acids, which yield both cis-diol and epoxide products.
研究了添加剂水杨酸、L-抗坏血酸和草酸在促进MnIV2(O)3(tmtacn)22（1(PF6)2，其中tmtacn = N,N',N''-三甲基-1,4,7-三氮杂环壬烷）催化H2O2对烯烃进行环氧化和顺式二羟基化反应以及抑制H2O2催化分解方面所起的作用。脂肪族和芳香族羧酸通过原位形成[MnIII2(μ-O)(μ-RCO2)2(tmtacn)2]2+型双核羧基桥联配合物来提高1的催化活性，而对于L-抗坏血酸和草酸，观察到反应活性存在显著差异。尽管与羧酸相比，L-抗坏血酸的反应混合物在光谱性质上存在关键差异，但原位形成的羧酸的参与是明显的。对于草酸，情况更为复杂，存在两种不同的催化体系；第一种仅参与环氧化反应，在草酸添加剂完全消耗之前占主导地位，此时原位形成的羧酸开始起到添加剂的作用，形成第二种不同的催化体系，即观察到的烷基和芳香族羧酸的催化体系，该体系能生成顺式二醇和环氧化产物。
