Chavan Suhas A, Maes Wouter, Gevers Lieven E M, Wahlen Joos, Vankelecom Ivo F J, Jacobs Pierre A, Dehaen Wim, De Vos Dirk E
Centre for Surface Chemistry and Catalysis, Katholieke Universiteit Leuven, Kasteelpark Arenberg 23, 3001 Leuven, Belgium.
Chemistry. 2005 Nov 4;11(22):6754-62. doi: 10.1002/chem.200500251.
The convergent synthesis of a series of porphyrin-functionalized pyrimidine dendrimers has been accomplished by a procedure involving the nucleophilic aromatic substitution (NAS) as a key reaction step. The resulting dendritic porphyrin catalysts show high activity in the light-induced generation of singlet oxygen ((1)O2) from ground-state oxygen. These materials are synthetically useful photosensitizers for the oxidation of various olefinic compounds to the corresponding allylic hydroperoxides. Catalytic activities and regio- and stereoselectivities of the dendritic photosensitizers are comparable to those observed for mononuclear porphyrin catalysts. Recycling of the dendrimer-enlarged homogeneous photocatalysts was possible by solvent-resistant nanofiltration (SRNF) by using an oxidatively stable membrane consisting of a polysiloxane polymer and ultrastable Y zeolite as inorganic filler. Moreover, this membrane technology provides a safe way to isolate the hydroperoxide products under very mild conditions. The membrane showed high retention for the macromolecular catalysts, even in chlorinated solvents, but some oxidative degradation of the porphyrin units of the dendrimer was observed over multiple catalytic runs.
通过以亲核芳香取代（NAS）作为关键反应步骤的方法，完成了一系列卟啉功能化嘧啶树枝状大分子的收敛合成。所得树枝状卟啉催化剂在光诱导基态氧生成单线态氧（¹O₂）方面表现出高活性。这些材料是用于将各种烯烃化合物氧化为相应烯丙基氢过氧化物的合成有用的光敏剂。树枝状光敏剂的催化活性、区域选择性和立体选择性与单核卟啉催化剂所观察到的相当。通过使用由聚硅氧烷聚合物和超稳定Y型沸石作为无机填料组成的氧化稳定膜，通过耐溶剂纳滤（SRNF）实现树枝状大分子放大的均相光催化剂的循环利用。此外，这种膜技术提供了一种在非常温和的条件下分离氢过氧化物产物的安全方法。该膜对大分子催化剂具有高保留率，即使在氯化溶剂中也是如此，但在多次催化运行中观察到树枝状大分子的卟啉单元有一些氧化降解。
