Phenylhydrazine (R) quantitatively reduces [Fe2(μ-O)(phen)4(H2O)2]4+ (1) (phen = 1,10-phenanthroline) and its conjugate base [Fe2(μ-O)(phen)4(H2O)(OH)]3+ (2) to [Fe(phen)3]2+ in presence of excess 1,10-phenanthroline in the pH range 4.12-5.55. Oxidation products of phenylhydrazine are dinitrogen and phenol. The reaction proceeds through two parallel paths: 1 + R → products (k1), 2 + R → products (k2); neither RH+ nor the doubly deprotonated conjugate base of the oxidant, [Fe2(μ-O)(phen)4(OH)2]2+ (3) is kinetically reactive though both are present in the reaction media. At 25.0°C, I = 1.0 M (NaNO3), the rate constants are k1 = 425 ± 10 M-1 s-1 and k2 = 103 ± 5 M-1 s-1. An inner-sphere, one-electron, rate-limiting step is proposed.