Preparation and characterization of mu-nitrido diiron phthalocyanines with electron-withdrawing substituents: application for catalytic aromatic oxidation

• Published in: Dalton transactions : an international journal of inorganic chemistry 2009-01 (36), p.7410-7420
• Main Authors: Işci, Umit, Afanasiev, Pavel, Millet, Jean-Marc M, Kudrik, Evgeny V, Ahsen, Vefa, Sorokin, Alexander B
• Format: Article
• Language: English
• Subjects: Catalysis; Catalytic Domain; Chemical Sciences; Enzymes - chemistry; Ferrous Compounds - chemical synthesis; Ferrous Compounds - chemistry; Indoles - chemistry; Iron - chemistry; Molecular Conformation; Oxidation-Reduction; Xylenes - chemistry
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/b902592h

Mu-nitrido-bis [tetra-(hexyl-sulfonyl)phthalocyaninatoiron] (3a) and mu-nitrido-bis [tetra-(tert-butylsulfonyl) phthalocyaninatoiron] (3b) complexes have been prepared and fully characterized by electrospray ionization mass spectrometry, UV-Vis, FTIR, EPR, Mössbauer techniques as well as by X-ray photoelectron and Fe K-edge X-ray absorption spectroscopies. Small changes at the periphery of the phthalocyanine ligand introduce a difference in the iron oxidation state. While 3b with tert-butyl substituents is a neutral complex with a mixed-valence Fe(3.5)-N-Fe(3.5) structural unit, 3a having n-hexyl substituents is an oxidized cationic Fe(IV)-N-Fe(IV) complex. The structural parameters of N-bridged diiron phthalocyanine with a Fe(3.5)-N-Fe(3.5) unit were determined for the first time. Iron atoms in 3b are displaced out of plane by 0.24 A and the Fe-N bond distance of the linear Fe-N-Fe fragment is equal to 1.67 A. Both complexes selectively catalyze benzylic oxidation of alkyl aromatic compounds by tBuOOH. Toluene was oxidized to benzoic acid with 80% selectivity, and the total turnover number was as high as 197. p-Toluic acid was the principal product of p-xylene oxidation. In this case the turnover number achieved 587 substrate molecules per molecule of catalyst. The described catalytic system is complementary to the recently reported system based on mu-nitrido diiron tetrabutylphthalocyanine-H2O2 which effectively oxidizes the benzene ring.