IRON(II) REDUCTANT (DH2)-INDUCED ACTIVATION OF DIOXYGEN FOR THE HYDROXYLATION OF AROMATIC-HYDROCARBONS AND PHENOLS - REACTION MIMIC FOR TYROSINE-HYDROXYLASE

Several iron(II) complexes [(Fe(II)L(x)); Fe-II(DPAH)(2) (DPAH(2) = 2,6-dicarboxylpyridine), Fe-II(PA)(2) (PAH = picolinic acid), and Fe-II(bpy)(2)(2+) (bpy = 2,2'-bipyridine)] in combination with a reductant [DH2; PhNHNHPh (mimic of dihydroflavin and tetrahydropterins)] catalytically activate O-2 (1 atm) for the hydroxylation of phenol and substituted phenols [e.g., PhOH --> o,p-C6H4(OH)(2); 4-XC(6)H(4)OH --> 4-XC(6)H(3)(OH)(2) (X = Cl, H, t-Bu, MeO)]. This chemistry, which appears to involve a Fenton-like reactive intermediate, [L(x)Fe(IV)OOH(DH)] (1c), mimics that of the tyrosine hydroxylase systems. With phenol as the reactant, the dominant product is catechol with the o/p ratio dependent on the DH3/Fe(II)L(x) ratio, As the latter approaches unity, catechol is favored. With Fe-II(DPAH)2 in 3:1 (mole ratio) acetonitrile/pyridine [(MeCN)(3)py], the relative reactivity for a series of substituted phenols (4-XC(6)H(4)OH; X = Cl, H, r-Bu, MeO) is substituent dependent: Cl > H > t-Bu > MeO.