?-nitrido diiron phthalocyanines: Electron-withdrawing vs electron-donating substituent effect on oxidation reaction catalysis

Abstract

Two mu-nitrido phthalocyanine complexes tetra non-peripherally substituted with either electron-withdrawing hexylsulfonyl chains ([FePc(SO(2)Hex)(4)](2)N) or electron-donating hexyloxy chains ([FePc(OHex)(4)](2)N) were prepared and fully characterized by FT-IR, MALDI-MS and UV-vis spectroscopic techniques, to investigate the effect of the substitution pattern on their catalytic properties. Iron atoms in both mu-nitrido complexes are in the Fe-IV-N=Fe-IV oxidation state, hence under their cationic form, as evidenced by the N3 peak in FT-IR and the fact that they are EPR silent. Both [FePc(SO(2)Hex)(4)](2)N and [FePc(OHex)(4)](2)N complexes were tested as catalysts for the oxidation of different benzyl alcohols by tBuOOH and gave the corresponding benzoic acids with excellent selectivity and complete conversion. The electron-withdrawing hexylsulfonyl-substituted mu-nitrido complex [FePc(SO(2)Hex)(4)](2)N exhibited slightly better catalytic activities and selectivity towards the benzoic acid products than the electron-donating hexyloxy substituted mu-nitrido complex [FePc(OHex)(4)](2)N.