Disproportionation Of O-Methylhydroxylamine Catalyzed By Aquapentacyanoferrate(Ii)

The aquapentacyanoferrate(II) ion, [Fe-II(CN)(5)-H2O](3-), catalyzes the disproportionation reaction of O-methylhydroxylamine, NH2OCH3, with stoichiometry 3NH(2)OCH(3) -> NH3 + N-2 + 3CH(3)OH. Kinetic and spectroscopic evidence support an initial N coordination of NH2OCH3 to [Fe-II(CN)(5)center dot H2O](3-) followed by a homolytic scission leading to radicals [Fe-II(CN)(5)center dot NH2](3-) (a precursor of Fe(III) centers and bound NH3) and free methoxyl, CH3O center dot, thus establishing a radical path leading to N-methoxyamino ((NHOCH3)-N-center dot) and 1,2-dimethoxyhydrazine, (NHOCH3)(2). The latter species is moderately stable and proposed to be the precursor of N-2 and most of the generated CH3OH. Intermediate [Fe-III(CN)(5)L](2-) complexes (L = NH3, H2O) form dinuclear cyano-bridged mixed-valent species, affording a catalytic substitution of the L ligands promoted by [FeIII(CN)(5)L](3-). Free or bound NH2OCH3 may act as reductants of [Fe-II(CN)(5)H2O](2-), thus regenerating active sites. At increasing concentrations of NH2OCH3 a coordinated diazene species emerges, [Fe-II(CN)(5)H2O](3-), which is consumed by the oxidizing CH3O center dot, giving N-2 and CH3OH. Another side reaction forms [Fe-II(CN)(5)H2O](3-), an intermediate containing the nitrosomethane ligand, which is further oxidized to the nitroprusside ion, [Fe-II(CN)(5)H2O](2-). The latter is a final oxidation product with a significant conversion of the initial [Fe-II(CN)(5)H2O](3-) complex. The side reaction partially blocks the Fe(II) aqua active site, though complete inhibition is not achieved because the radical path evolves faster than the formation rates of the Fe-II-NO+ bonds.