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Porphyrin‐Functionalized Dendrimers: Synthesis and Application as Recyclable Photocatalysts in a Nanofiltration Membrane Reactor
Author(s) -
Chavan Suhas A.,
Maes Wouter,
Gevers Lieven E. M.,
Wahlen Joos,
Vankelecom Ivo F. J.,
Jacobs Pierre A.,
Dehaen Wim,
De Vos Dirk E.
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500251
Subject(s) - dendrimer , porphyrin , chemistry , catalysis , singlet oxygen , membrane , allylic rearrangement , nanofiltration , solvent , photochemistry , organic chemistry , polymer chemistry , combinatorial chemistry , oxygen , biochemistry
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 O 2 ) 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.