Polystyrene and polymethacrylate resin-supported Jacobsen’s alkene epoxidation catalyst
作者:Laetitia Canali、Elaine Cowan、Hervé Deleuze、Colin L. Gibson、David C. Sherrington
DOI:10.1039/b002118k
日期:——
Polystyrene and polymethacrylate-based resin supported Jacobsenâs chiral Mn salen complexes have been prepared. The resins are of defined molecular structure and morphology, and the complexes have been attached primarily in a pendant fashion. The loadings of Mn(III) are in the range â0.08â0.35 mmol gâ1 to maximise the likelihood of site-isolation. The polymer-supported complexes have been used as enantioselective catalysts in the epoxidation of 1,2-dihydronaphthalene, indene, 1-phenylcyclohex-1-ene and 1-phenyl-3,4-dihydronaphthalene using m-chloroperbenzoic acid as the oxidant and 4-methylmorpholine N-oxide as the co-oxidant. Though the activities of the polymer catalysts are reduced relative to the soluble homogeneous analogue, the catalysts are sufficiently active to be useful. The corresponding reduction in enantioselectivity is more significant, and is both substrate and polymer resin dependent. However, in the case of 1-phenylcyclohex-1-ene and a macroporous polymethacrylate-based resin the enantioselectivity is equivalent to that of the soluble complex (91â92% ee). This is the first report of a polymer-supported analogue of Jacobsenâs catalyst being as selective as the homogeneous species. The catalysis data is discussed in detail in the context of the design of the polymer-supported system, and the existing data already available in the literature.
Attempts have also been made to recycle the polymer catalysts with and without re-loading of Mn. In fact the level of leaching of Mn is very low, but the catalysts show a very rapid fall off in both activity and selectivity in the first and second cycles. Overall therefore it seems that the intrinsic stability of the chiral Mn(II) salen complex itself is too low to allow viable recycling, and the development of other more stable supported chiral metal salen complexes for use in other enantioselective reactions seems a better future option.
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我们制备了聚苯乙烯和聚甲基丙烯酸酯基树脂支持的雅各布森手性锰沙林络合物。这些树脂具有明确的分子结构和形态,络合物主要以悬垂方式附着。锰(III)的负载量范围为 0.08â0.35 mmol gâ1 ,以最大限度地提高位点分离的可能性。聚合物支撑复合物被用作对映体选择性催化剂,以间氯过苯甲酸为氧化剂,4-甲基吗啉 N-氧化物为助氧化剂,对 1,2-二氢萘,茚,1-苯基环己-1-烯和 1-苯基-3,4-二氢萘进行环氧化反应。虽然与可溶性均相类似物相比,聚合物催化剂的活性有所降低,但其活性足以发挥作用。对映体选择性的相应降低更为显著,并且与底物和聚合物树脂有关。不过,在 1-苯基环己-1-烯和大孔聚甲基丙烯酸酯基树脂的情况下,对映体选择性与可溶性复合物相当(91%-92% ee)。这是首次报道聚合物支撑的雅各布森催化剂类似物具有与均相催化剂相同的选择性。我们结合聚合物支撑系统的设计以及文献中已有的数据,对催化数据进行了详细讨论。 我们还尝试在锰重载或不重载的情况下回收聚合物催化剂。事实上,锰的沥滤水平非常低,但催化剂在第一和第二个循环中的活性和选择性都迅速下降。因此,总体看来,手性 Mn(II) salen 复合物本身的内在稳定性太低,无法进行可行的回收利用,而开发其他更稳定的支撑手性金属 salen 复合物用于其他对映体选择性反应似乎是未来更好的选择。