Stability and reactivity of low-spin ferric hydroperoxo and alkylperoxo complexes with bipyridine and phenantroline ligands

In this work the first-order rate constants of self-decomposition of hydrop eroxo and alkylperoxo complexes [Fe(bpr)(2)(OOH)Py](NO3)(2) (2a-Py), [Fe(ph en)(2)(OOH)Py](NO3)(2) (2b-Py) and [Fe(bpy)(2)(OOtBu)CH3CN](NO3)(2) (3a-CH3 CN) were determined in the presence of various substrates and at various te mperatures. It was observed, that the alkylperoxo species are far less stab le than corresponding hydroperoxo intermediates, k = 1.2 x 10(-2) s(-1) (3a -CH3CN in CH,CN at - 10 degrees C) and k = 2 x 10(-4) s(-1) (2a-Py in CH3CN at - 10 degrees C). The sixth ligand (Py in 2a-Py and 2b-Py; CH,CN in 3a-C H3CN) can be replaced by other donor molecules B in appropriate solvent sys tems. Using d(9)-tBuOOH, D-2 NMR signals of tBuOO moieties of complexes 3a- CH3CN, 3a-CH3OH and 3a-H2O were observed. The rate of decomposition of hydr operoxo complexes [Fe(bpy)(2)(OOH)B](NO3)(2) (2a-B), where B are derivative s of Py (3-Br-Py, 3-Me-Py, 4-Me-Py and 4-Me2N-Py) increases with the growth of basisity of B (push effect). Such effect is markedly smaller for alkylp eroxo species [Fe(bpy)(2)(OOtBu)B](NO3)(2) (3a-B). The addition of organic substrates (cyclohexane, cyclohexene, methyl phenyl sulfide) in concentrati ons up to 3 M at -10 degrees C to +20 degrees C does not noticeably change the rate of self-decomposition of 2a-B, [Fe(phen)(2)(OOH)B](NO3)(2) (2b-B) and 3a-B. Thus the intermediates concerned do not directly react with organ ic substrates. The reactivity patterns of 2a-B, 2b-B and 3a-B were characte ristic for free radical oxidation. OH. and HO2. radicals were trapped in so lution containing 2a-Py, and tBuOO(.) free radicals were detected in soluti on in the presence of 3a-B. The determined rates of self-decomposition of c omplexes 2a-B, 2b-B and 3a-B can be used for evaluation of the upper limit for their reactivity towards organic substrates. (C) 2000 Elsevier Science B.V. All rights reserved.