Reactions of Hydroxylamine with Metal Porphyrins

Abstract

The reaction of hydroxylamine with a series of metal porphyrins was examined in methanol/chloroform media. The reductive nitrosylation reaction was observed for the manganese and iron porphyrins, leading to a nitrosyl complex that precipitated out of the solution in good isolatable yield (80-90%). This reaction could be used synthetically for the generation of iron and manganese porphyrin nitrosyl complexes and was particularly useful for making isotopically labeled nitrosyl complexes. On the other hand, Co(II)(TPP) and Cr(TPP)(Cl) did not react with hydroxylamine under anaerobic conditions. With trace amounts of oxygen, the reaction of Co(II)(TPP) with hydroxylamine led to the formation of a stable cobalt(III)-bis(hydroxylamine) complex. The infrared, resonance Raman, and proton NMR spectra were consistent with a cobalt(III)-bis(hydroxylamine) complex. The cyclic voltammetry and visible spectroelectrochemistry of this complex were examined. The one-electron reduction of Co(III)(TPP)(NH(2)OH)(2)(+) formed Co(II)(TPP), for which there was no evidence for the coordination of hydroxylamine. Further reduction led to Co(I)(TPP)(-), which reacted with the halogenated solvent to form a cobalt-alkyl complex. The difference in the reactivity of these four metal porphyrins with hydroxylamine correlated well with their E(1/2) values. Iron(III) and manganese(III) porphyrins were relatively easy to reduce and readily underwent the reductive nitrosylation reaction, while cobalt(II) and chromium(III) porphyrins are unreactive. The one-electron oxidation of the hydroxylamine complex with a M(III) porphyrin would be expected to oxidize the N-atom in the coordinated hydroxylamine. The oxidation of M(III)(NH(2)OH) with the loss of a proton would form M(II)(N(I)H(2)O)(+) by an internal electron transfer, which will eventually lead to M(NO). The relationship between the reductive nitrosyl reaction and the enzymatic interconversion of NO and hydroxylamine was discussed.

Disproportionation of hydroxylamine by water-soluble iron(III) porphyrinate compounds

“…Differing from previous results with [Fe III (TPP)] + in organic solutions [17,36] 5À after dissociation (k off = 6.3 Â 10 À4 s À1 ) [37], and reoxidation (Fig. 2).…”

“…2 ], prior to a catalytic disproportionation reaction yielding [Fe II (TPP)(NO)] and excess NH 3 , described as an intramolecular electron transfer or through the reaction of HA with the initially formed bis-coordinated complex [28]. The reaction of HA with Fe III TPP indeed provides a synthetic method for [Fe II (TPP)-(NO)] [17]. The formation of [Fe II (Porph)(H 2 NR)] or [Fe II (Porph)-(H 2 NR) 2 ] by autoreduction of porphyrinates with alkyl or aryl amines has also been reported previously [29].…”

“…HA also appears as a biologically relevant NO-donor, favoring vasodilation when put in contact with mixtures of catalase-H 2 O 2 [12,13] or in the presence of myoglobin and H 2 O 2 [14] More specialized, the multiheme enzyme hydroxylamine oxidoreductase (HAO) from the autotrophic bacteria Nitrosomonas europaea catalyzes the conversion of HA to NO À 2 [15,16]. In organic media, the reactions of certain [Fe III (Porph)] with HA yield nearly quantitatively [Fe II (Porph)(NO)], and only NH 3 has been found as an additional product [17].…”

Interaction between Dioxoruthenium(VI) Porphyrins and Hydroxylamines: Coordination ofN-Substituted Hydroxylamine to Ruthenium and X-ray Crystal Structures of Ruthenium Complexes with a Unidentate Nitrosoarene Ligand

“…We notice that previous reports on the interaction between synthetic metalloporphyrins and hydroxylamines are extremely rare. Besides those on the foregoing ª[Fe III (Por)Cl] RNHOH (R Me, iPr, PhCH 2 CH 2 )º systems, the only others are by Ryan and coworkers [22,23] mainly on the reaction of [M III (Por)Cl] (M Fe, Mn) with NH 2 OH to form nitrosyl metalloporphyrins. Conspicuously, no oxometalloporphyrins have been found to react with hydroxylamines to form nitroso or nitrosyl complexes.…”

Structural, 103Rh NMR and DFT Studies of a Bis(phosphane)RhIII–Porphyrin Derivative

“…Similar porphyrin ring current induced shieldings are known for other low-spin d 6 metalloporphyrins. [31,32] From the 1 H NMR spectra of 1 above 253 K ( Figure S4), the axial ligands and meso-phenyl groups are in the fast exchange limit on the 500 MHz NMR timescale.…”