Jónsson Stefán, Odille Fabrice G J, Norrby Per-Ola, Wärnmark Kenneth
Organic Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00, Lund, Sweden.
Org Biomol Chem. 2006 May 21;4(10):1927-48. doi: 10.1039/b518244a. Epub 2006 Apr 19.
The synthesis of the components of the dynamic supramolecular hydrogen-bonded catalytic system 2 + 3 is described. The catalytic performance and substrate- and enantioselectivity of Mn(salen) catalyst 2 were investigated in the presence and absence of the Zn(porphyrin) receptor unit 3. The effects of pyridine and pyridine N-oxide donor ligands were also studied. Some aspects on the mechanism of the Jacobsen-Katsuki epoxidation, based on literature observations, are introduced as a means to analyse the behaviour of 2 and its modulation by the formation of macrocycle 1 with 3. A complete association model of the metal-free system 4 + 5 refutes the earlier assumption that macrocycle 1 is the predominant form of catalyst 2 under the standard epoxidation reaction conditions with 2 + 3. Evidence are provided that receptor-binding substrates and nonbinding substrates, respectively, are epoxidised by two different catalytic species, or two distinct distributions of species in competitive epoxidations using catalytic system 2 + 3. The two species are assigned to the endo and exo faces of the Mn(salen) catalyst in macrocycle 1, and to equivalently folded oligomeric structures with monomers 2 and 3 in adjacent positions.
描述了动态超分子氢键催化体系2 + 3各组分的合成。研究了在存在和不存在锌卟啉受体单元3的情况下，Mn(salen)催化剂2的催化性能以及底物选择性和对映选择性。还研究了吡啶和吡啶N - 氧化物供体配体的影响。基于文献观察，介绍了雅各布森 - 胜木环氧化反应机理的一些方面，以此作为分析2的行为及其与3形成大环1时的调控作用的一种手段。无金属体系4 + 5的完整缔合模型驳斥了先前的假设，即在2 + 3的标准环氧化反应条件下，大环1是催化剂2的主要形式。有证据表明，受体结合底物和非结合底物分别由两种不同的催化物种进行环氧化，或者在使用催化体系2 + 3的竞争性环氧化反应中由两种不同的物种分布进行环氧化。这两种物种分别对应于大环1中Mn(salen)催化剂的内表面和外表面，以及相邻位置具有单体2和3的等效折叠低聚结构。
