Dataset Information

Effects of N2 Binding Mode on Iron-Based Functionalization of Dinitrogen to Form an Iron(III) Hydrazido Complex.

ABSTRACT: Distinguishing the reactivity differences between N2 complexes having different binding modes is crucial for the design of effective N2-functionalizing reactions. Here, we compare the reactions of a K-bridged, dinuclear FeNNFe complex with a monomeric Fe(N2) complex where the bimetallic core is broken up by the addition of chelating agents. The new anionic iron(0) dinitrogen complex has enhanced electron density at the distal N atoms of coordinated N2, and though the N2 is not as weakened in this monomeric compound, it is much more reactive toward silylation by (CH3)3SiI (TMSI). Double silylation of N2 gives a three-coordinate iron(III) hydrazido(2-) complex, which is finely balanced between coexisting S = 1/2 and S = 3/2 states that are characterized by crystallography, spectroscopy, and computations. These results give insight into the interdependence between binding modes, alkali dependence, reactivity, and magnetic properties within an iron system that functionalizes N2.

SUBMITTER: McWilliams SF

PROVIDER: S-EPMC6115203 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Effects of N2 Binding Mode on Iron-Based Functionalization of Dinitrogen to Form an Iron(III) Hydrazido Complex.

McWilliams Sean F SF Bill Eckhard E Lukat-Rodgers Gudrun G Rodgers Kenton R KR Mercado Brandon Q BQ Holland Patrick L PL

Journal of the American Chemical Society 20180629 27

Distinguishing the reactivity differences between N2 complexes having different binding modes is crucial for the design of effective N2-functionalizing reactions. Here, we compare the reactions of a K-bridged, dinuclear FeNNFe complex with a monomeric Fe(N2) complex where the bimetallic core is broken up by the addition of chelating agents. The new anionic iron(0) dinitrogen complex has enhanced electron density at the distal N atoms of coordinated N2, ...[more]

PMID: 29957940

Similar Datasets

Project description:Nitrogenase reduces dinitrogen (N2) by six electrons and six protons at an active-site metallocluster called FeMo cofactor, to yield two ammonia molecules. Insights into the mechanism of substrate reduction by nitrogenase have come from recent successes in trapping and characterizing intermediates generated during the reduction of protons as well as nitrogenous and alkyne substrates by MoFe proteins with amino acid substitutions. Here, we describe an intermediate generated at a high concentration during reduction of the natural nitrogenase substrate, N2, by wild-type MoFe protein, providing evidence that it contains N2 bound to the active-site FeMo cofactor. When MoFe protein was frozen at 77 K during steady-state turnover with N2, the S = 3/2 EPR signal (g = [4.3, 3.64, 2.00]) arising from the resting state of FeMo cofactor was observed to convert to a rhombic, S = 1/2, signal (g = [2.08, 1.99, 1.97]). The intensity of the N2-dependent EPR signal increased with increasing N2 partial pressure, reaching a maximum intensity of approximately 20% of that of the original FeMo cofactor signal at > or = 0.2 atm N2. An almost complete loss of resting FeMo cofactor signal in this sample implies that the remainder of the enzyme has been reduced to an EPR-silent intermediate state. The N2-dependent EPR signal intensity also varied with the ratio of Fe protein to MoFe protein (electron flux through nitrogenase), with the maximum signal intensity observed with a ratio of 2:1 (1:1 Fe protein:FeMo cofactor) or higher. The pH optimum for the signal was 7.1. The N2-dependent EPR signal intensity exhibited a linear dependence on the square root of the EPR microwave power in contrast to the nonlinear response of signal intensity observed for hydrazine-, diazene-, and methyldiazene-trapped states. 15N ENDOR spectroscopic analysis of MoFe protein captured during turnover with 15N2 revealed a 15N nuclear spin coupled to the FeMo cofactor with a hyperfine tensor A = [0.9, 1.4, 0.45] MHz establishing that an N2-derived species was trapped on the FeMo cofactor. The observation of a single type of 15N-coupled nucleus from the field dependence, along with the absence of an associated exchangeable 1H ENDOR signal, is consistent with an N2 molecule bound end-on to the FeMo cofactor.

Project description:Redox-inactive metal ions that function as Lewis acids play pivotal roles in modulating reactivities of oxygen-containing metal complexes in a variety of biological and biomimetic reactions, including dioxygen activation/formation and functionalization of organic substrates. Mononuclear nonheme iron(III)-peroxo species are invoked as active oxygen intermediates in the catalytic cycles of dioxygen activation by nonheme iron enzymes and their biomimetic compounds. Here, we report mononuclear nonheme iron(III)-peroxo complexes binding redox-inactive metal ions, [(TMC)FeIII(O2)]+-M3+ (M3+ = Sc3+ and Y3+; TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), which are characterized spectroscopically as a 'side-on' iron(III)-peroxo complex binding a redox-inactive metal ion, (TMC)FeIII-(?,?2:?2-O2)-M3+ (2-M). While an iron(III)-peroxo complex, [(TMC)FeIII(O2)]+, does not react with electron donors (e.g., ferrocene), one-electron reduction of the iron(III)-peroxo complexes binding redox-inactive metal ions occurs readily upon addition of electron donors, resulting in the generation of an iron(IV)-oxo complex, [(TMC)FeIV(O)]2+ (4), via heterolytic O-O bond cleavage of the peroxide ligand. The rates of the conversion of 2-M to 4 are found to depend on the Lewis acidity of the redox-inactive metal ions and the oxidation potential of the electron donors. We have also determined the fundamental electron-transfer properties of 2-M, such as the reduction potential and the reorganization energy in electron-transfer reaction. Based on the results presented herein, we have proposed a mechanism for the reactions of 2-M and electron donors; the reduction of 2-M to the reduced species, (TMC)FeII-(O2)-M3+ (2'-M), is the rate-determining step, followed by heterolytic O-O bond cleavage of the reduced species to form 4. The present results provide a biomimetic example demonstrating that redox-inactive metal ions bound to an iron(III)-peroxo intermediate play a significant role in activating the peroxide O-O bond to form a high-valent iron(IV)-oxo species.

Dataset Information

Effects of N2 Binding Mode on Iron-Based Functionalization of Dinitrogen to Form an Iron(III) Hydrazido Complex.

Publications

Effects of N<sub>2</sub> Binding Mode on Iron-Based Functionalization of Dinitrogen to Form an Iron(III) Hydrazido Complex.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets