Investigation of phthalocyanine catalysts for the aerobic synthesis of meso-substituted porphyrins

✍ Scribed by M. Ravikanth; Catalina Achim; John S. Tyhonas; Eckard Münck; Jonathan S. Lindsey

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 166 KB
• Volume: 01
• Category: Article
• ISSN: 1088-4246
• DOI: 10.1002/(sici)1099-1409(199710)1:4<385::aid-jpp42>3.0.co;2-i

✦ Synopsis

The aerobic oxidation process for the synthesis of porphyrins, previously performed using 5 mol % p-chloranil (TCQ), 5 mol % iron(II) phthalocyanine (FePc) and stoichiometric amounts of O 2 , has been refined using new phthalocyanine catalysts. Four phthalocyanine catalysts have been prepared, characterized by M össbauer spectroscopy and examined for efficacy in the high concentration (0.1 M) synthesis of tetraphenylporphyrin at room temperature. Each phthalocyanine has been identified to be a µ-oxo dimer. Two catalysts are soluble (the µ-oxo dimers [(t-butyl) 4 FePc] 2 O and [(n-C 6 H 13 O) 4 FePc] 2 O) and enable homogeneous reactions, while two are insoluble (the µ-oxo(1) and µ-oxo(2) dimers of FePc, (FePc) 2 O) and give heterogeneous reactions. These four phthalocyanine compounds provide efficient catalysis at the 0.3-1 mol % level using only 1 mol % quinone or hydroquinone (TCQ, DDQ, TCQH 2 or DDQH 2 ), affording ~25% yields of tetraphenylporphyrin in 60 min of oxidation. There are no discernible advantages of the homogeneous versus heterogeneous catalysts. The µ-oxo dimers are active, but FePc is inactive, at the 0.3 mol % level. The activity of the FePc sample at the 5 mol % level is attributed to residual µ-oxo dimer impurity. This aerobic oxidation process is superior to stoichiometric oxidation with TCQ or DDQ, and can be performed in the presence of BF 3 •O(Et) 2 , trifluoroacetic acid, or under neutral conditions.