Electrochemistry of Nitrite Reductase Model Compounds. 3. Formation and Characterization of a Bis(hydroxylamine)(tetraphenylporphyrinato)Iron(II) Complex

Authors

Diwei Feng, Marquette University
Michael D. Ryan, Marquette UniversityFollow

Document Type

Article

Language

eng

Format of Original

4 p.

Publication Date

7-1-1987

Publisher

American Chemical Society

Source Publication

Inorganic Chemistry

Source ISSN

0020-1669

Abstract

The reaction of hydroxylamine with Fe^III(TPP)CI and Fe^II(TPP) (TPP = tetraphenylprphyrinate(2-)) at room temperature and at lower temperatures (<-20 °C) was studied in this work. At room temperature, hydroxylamine reacted with both Fe^III- and Fe^II(TPP) to form Fe(TPP)(NO). But, when the temperature was reduced to -40 °C in methylene chloride, Fe(TPP)(NH₂OH)₂ was stable. This complex was characterized by visible and NMR spectroscopy and by electrochemistry. The visible and NMR spectra of Fe(TPP)(NH₂OH)₂ were similar to other low-spin six-coordinate ferrous TPP complexes. As was consistent with this low spin (S = 0) formulation, the chemical shifts of the porphyrin and hydroxylamine resonances were independent of temperature. In addition, the resonances due to the coordinated hydroxylamine were observed upfield from Me₄Si. The same Fe(TPP)(NH₂OH)₂ complex can be formed from Fe(TPP)Cl and hydroxylamine, where the excess hydroxylamine can reduce the iron. The Fe- (TPP)-hydroxylamine complex was stable at low temperatures, but it decomposed at room temperature to Fe(TPP)(NO). Conversely, when Fe(TPP)NO and hydroxylamine were mixed together at low temperatures, Fe(TPP)(NH₂OH)₂ was formed. Cyclic voltammetry of this complex was carried out at -35 °C. The first reduction wave was observed with an E_1/2 value of -1.22 V vs. a Ag/AgNO₃ reference electrode, while the first oxidation wave occurred at an E_1/2 value of -0.18 V vs. Ag/AgNO₃. Coulometric oxidation of the complex at -35 °C at 0.1 V vs. Ag/AgNO₃ gave a coulometric n value of 3, and the final oxidation product was Fe(TPP)(NO). The voltammetric data were consistent with an initial formation of a ferric complex, which underwent subsequent reaction to form the nitrosyl complex.

Comments

Inorganic Chemistry, Vol. 26, No. 15 (July 1, 1987): 2480-2483. DOI.

Recommended Citation

Feng, Diwei and Ryan, Michael D., "Electrochemistry of Nitrite Reductase Model Compounds. 3. Formation and Characterization of a Bis(hydroxylamine)(tetraphenylporphyrinato)Iron(II) Complex" (1987). Chemistry Faculty Research and Publications. 513.
https://epublications.marquette.edu/chem_fac/513