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A pentadentate [N5] ligand (N2Py2Pz) based on the classic N4Py (N,N-bis (2-pyridylmethyl)- N- bis(2-pyridyl) methylamine) framework has been synthesized by replacing the two pyridylmethyl arms with corresponding (N-methyl) pyrazolylmethyl units to form [N-bis(1-methyl- 2- pyrazolyl) methyl-N- (bis-2- pyridylmethyl) amine] (L1). The oxidation of the iron(II) precursor (N2Py2Pz)FeII(OTf)2 (1) with (tBuSO2)C6H4IO at 298 K leads to the formation of the [FeIV(O)(N2Py2Pz)]2+ intermediate (2) with a near-IR band at 750 nm (εM = 250 M-1cm-1) and a t1/2 ~ 2 min at 298 K. The introduction of the less basic pyrazolylmethyl ligands in place of two pyridylmethyl units generates FeIV=O intermediate 2 that exhibits a cyclohexane oxidation rate of 0.29 s-1 at 298 K, which is 5,000-fold faster than that observed for the classic FeIV(O)N4Py parent complex and 40,000-fold more reactive than the least reactive FeIV(O)N2Py2Q' complex in this series (Py = pyridine, Q' = isoquinoline) recently reported by Nordlander. high-valent. [ABSTRACT FROM AUTHOR]

Reaction of [Fe2 (N-Et-HPTB)-(CH3COS)](BF4)2 (1) with (NO)(BF4) produces a nonheme mononitrosyl diiron(II) complex, [Fe2(N-Et- HPTB)(NO)(DMF)3](BF4)3 (2). Complex 2 is the first example of a [FeII{Fe(NO)}7] species and is also the first example of a mononitrosyl diiron(II) complex that mediates the reduction of NO to N2O. This work describes the selective synthesis, detailed characterization and NO reduction activity of 2 and thus provides new insights regarding the mechanism of flavodiiron nitric oxide reductases. [ABSTRACT FROM AUTHOR]

Nonheme iron enzymes utilize S = 2 iron(IV)-oxo intermediates as oxidants in biological oxygenations. In contrast, corresponding synthetic nonheme Fe IV ═O complexes characterized to date favor the S = 1 ground state that generally shows much poorer oxidative reactivity than their S = 2 counterparts. However, one intriguing exception found by Nam a decade ago is the S = 1 [Fe IV (O)(Me 3 NTB)] 2+ complex (Me 3 NTB = [tris(( N -methyl-benzimidazol-2-yl)methyl)amine], 1O ) with a hydrogen atom transfer (HAT) reactivity that is 70% that of the S = 2 [Fe IV (O)(TQA)] 2+ complex (TQA = tris(2-quinolylmethyl)amine, 3O ). In our efforts to further explore this direction, we have unexpectedly uncovered a family of new S = 1 complexes with HAT reaction rates beyond the currently reported limits in the tripodal ligand family, surpassing oxidation rates found for the S = 2 [Fe IV (O)(TQA)] 2+ complex by as much as an order of magnitude. This is achieved simply by replacing the secondary sphere methyl groups of the Me 3 NTB ligand with larger cycloalkyl-CH 2 (R groups in 2O R ) moieties ranging from c -propylmethyl to c -hexylmethyl. These 2O R complexes show Mössbauer data at 4 K and 1 H NMR spectra at 193 and 233 K that reveal S = 1 ground states, in line with DFT calculations. Nevertheless, they give rise to the most reactive synthetic nonheme oxoiron(IV) complexes found to date within the tripodal ligand family. Our DFT study indicates transition state stabilization through entropy effects, similar to enzymatic catalysis.

Flavodiiron nitric oxide reductases (FNORs) protect microbes from nitrosative stress under anaerobic conditions by mediating the reduction of nitric oxide (NO) to nitrous oxide (N 2 O). The proposed mechanism for the catalytic reduction of NO by FNORs involves a dinitrosyldiiron intermediate with a [hs-{FeNO} 7 ] 2 formulation, which produces N 2 O and a diferric species. Moreover, both NO and hydrogen sulfide (H 2 S) have been implicated in several similar physiological functions in biology and are also known to cross paths in cell signaling. Here we report the synthesis, spectroscopic and theoretical characterization, and N 2 O production activity of an unprecedented monohydrosulfidodinitrosyldiiron compound, with a [(HS)hs-{FeNO} 7 /hs-{FeNO} 7 ] formulation, that models the key dinitrosyl intermediate of FNORs. The generation of N 2 O from this unique compound follows a semireduced pathway, where one-electron reduction generates a reactive hs-{FeNO} 8 center via the occupation of an Fe-NO antibonding orbital. In contrast to the well-known reactivity of H 2 S and NO, the coordinated hydrosulfide remains unreactive toward NO and acts only as a spectator ligand during the NO reduction process.