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Conversion of a Fleeting Open-Shell Iron Nitride into an Iron Nitrosyl.

ABSTRACT: Terminal metal nitrides have been proposed as key intermediates in a series of pivotal chemical transformations. However, exploring the chemical activity of transient tetragonal iron(V) nitrides is largely impeded by their facile dimerization in fluid solutions. Herein, in?situ EPR and Mössbauer investigations are presented of unprecedented oxygenation of a paramagnetic iron(V) nitrido intermediate, [Fe^V N(cyclam-ac)]⁺ (2, cyclam-ac^- =1,4,8,11-tetraazacyclotetradecane-1-acetate anion), yielding an iron nitrosyl complex, [Fe(NO)(cyclam-ac)]⁺ (3). Further theoretical studies suggest that during the reaction a closed-shell singlet O atom is transferred to 2. Consequently, the N-O bond formation does not follow a radical coupling mechanism proposed for the N-N bond formation but is accomplished by three mutual electron-transfer pathways between 2 and the O atom donor, thanks to the ambiphilic nature of 2.

SUBMITTER: Chang HC

PROVIDER: S-EPMC6899486 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Conversion of a Fleeting Open-Shell Iron Nitride into an Iron Nitrosyl.

Chang Hao-Ching HC Lin Yen-Hao YH Werlé Christophe C Neese Frank F Lee Way-Zen WZ Bill Eckhard E Ye Shengfa S

Angewandte Chemie (International ed. in English) 20191022 49

Terminal metal nitrides have been proposed as key intermediates in a series of pivotal chemical transformations. However, exploring the chemical activity of transient tetragonal iron(V) nitrides is largely impeded by their facile dimerization in fluid solutions. Herein, in situ EPR and Mössbauer investigations are presented of unprecedented oxygenation of a paramagnetic iron(V) nitrido intermediate, [FeV N(cyclam-ac)]+ (2, cyclam-ac- =1,4,8,11-tetraazacyclotetrad ...[more]

PMID: 31532866

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Project description:We use quantitative experimental and theoretical approaches to characterize the vibrational dynamics of the Fe atom in porphyrins designed to model heme protein active sites. Nuclear resonance vibrational spectroscopy (NRVS) yields frequencies, amplitudes, and directions for 57Fe vibrations in a series of ferrous nitrosyl porphyrins, which provide a benchmark for evaluation of quantum chemical vibrational calculations. Detailed normal mode predictions result from DFT calculations on ferrous nitrosyl tetraphenylporphyrin Fe(TPP)(NO), its cation [Fe(TPP)(NO)]+, and ferrous nitrosyl porphine Fe(P)(NO). Differing functionals lead to significant variability in the predicted Fe-NO bond length and frequency for Fe(TPP)(NO). Otherwise, quantitative comparison of calculated and measured Fe dynamics on an absolute scale reveals good overall agreement, suggesting that DFT calculations provide a reliable guide to the character of observed Fe vibrational modes. These include a series of modes involving Fe motion in the plane of the porphyrin, which are rarely identified using infrared and Raman spectroscopies. The NO binding geometry breaks the four-fold symmetry of the Fe environment, and the resulting frequency splittings of the in-plane modes predicted for Fe(TPP)(NO) agree with observations. In contrast to expectations of a simple three-body model, mode energy remains localized on the FeNO fragment for only two modes, an N-O stretch and a mode with mixed Fe-NO stretch and FeNO bend character. Bending of the FeNO unit also contributes to several of the in-plane modes, but no primary FeNO bending mode is identified for Fe(TPP)(NO). Vibrations associated with hindered rotation of the NO and heme doming are predicted at low frequencies, where Fe motion perpendicular to the heme is identified experimentally at 73 and 128 cm-1. Identification of the latter two modes is a crucial first step toward quantifying the reactive energetics of Fe porphyrins and heme proteins.

Dataset Information

Conversion of a Fleeting Open-Shell Iron Nitride into an Iron Nitrosyl.

Publications

Conversion of a Fleeting Open-Shell Iron Nitride into an Iron Nitrosyl.

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