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A dimeric dithiolate-bridged species, [Fe(NO)(PS2)] 2 ( 1 ) containing two {FeNO} 7 units, can be isolated by treating [Fe(CO) 2 (NO) 2 ] with PS2H 2 (PS2H 2 = bis(2-dimercaptophenyl)phenylphosphine). Crystallographic studies reveal the syn-configuration of NO units and the bridging thiolates in the butterfly shape of the 2Fe2S core. Addition of PPh 3 to the solution of dinuclear 1 leads to the formation of mononuclear {FeNO} 7 [Fe(NO)(PS2)(PPh 3 )] ( 2 ) that shows electrochemical responses similar to those of 1 . One-electron reduction of 1 with Cp* 2 Co or KC 8 results in the isolation of thiolate-bridged bimetallic DNIC, [(PS2)Fe(μ-PS2)Fe(NO) 2 ] - ([ 3 ] - ), confirmed by several spectroscopies including single-crystal X-ray diffraction studies. The bimetallic DNIC [ 3 ] - is a rare example obtained from the one-electron reduction of a dinuclear Fe-NO {FeNO} 7 model complex. With the assistance of redox behaviors of 2 , electrochemical studies imply that the reduction of 1 leads to the formation of a mononuclear {FeNO} 8 [Fe(NO)(PS2)(THF)] - intermediate, which involves disproportionation or NO - transfer to yield [ 3 ] - . Based on IR data and magnetic properties, the electronic structure of [ 3 ] - can be described as a Fe II /{Fe(NO) 2 } 9 state. Isolation of the {Fe(NO) 2 } 9 moiety coordinated by the Fe ancillary complex lends strong support to the NO scrambling behavior in the effectiveness of the activity of flavodiiron nitric oxide reductases (FNORs).

The one-electron oxidations of a Fe2 complex lead to the formation of a persistent metal-stabilized thiyl radical Fe2 species, mixed-valent Fe4, and Fe8 complexes. The unpaired spin in the Fe2 radical species delocalizes over the Fe2 and the aromatic dithiolate, mostly on the terminal sulfur. The subsequent dimerization of the singly oxidized Fe2 to the Fe4 retains the partial thiyl radical character. For an analogue with less steric hindrance, the π-π stacking interaction between the dithiolato aromatic rings induces generation of the Fe8, in which process electronic structures of the species are modulated through reducing the thiyl radical to the thiolate. Electronic reorganization repeats when the Fe8 is converted to Fe4. Electronic interplay in the complexes decreases the energy gap of frontier MOs and buffers electronic impacts upon redox events. Easier accessible redox potentials and increased stability of the species are facilitated. The results demonstrate that electronic versatility of the benzenedithiolate exerts pronounced influences on electronic and coordination structure of the metal complexes., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Attachment of the redox-active C(60)(H)PPh(2) group modulates the electronic structure of the Fe(2) core in [(μ-bdt)Fe(2)(CO)(5)(C(60)(H)PPh(2))]. The neutral complex is characterized by X-ray crystallography, IR, NMR spectroscopy, and cyclic voltammetry. When it is reduced by one electron, the spectroscopic and density functional theory results indicate that the Fe(2) core is partially spin-populated. In the doubly reduced species, extensive electron communication occurs between the reduced fullerene unit and the Fe(2) centers as displayed in the spin-density plot. The results suggest that the [4Fe4S] cluster within the H cluster provides an essential role in terms of the electronic factor.

A series of iron azadithiolate complexes possessing an intramolecular secondary coordination sphere interaction and an ability to reduce HOAc at the potential near the first electron-transfer process are reported. A unique structural feature in which the aza nitrogen has its lone pair point toward the apical carbonyl carbon is observed in [Fe(2)(mu-S(CH(2))(2)NR(CH(2))(2)S)(CO)(6-x)L(x)](2) (R = (n)Pr, x = 0, 1a; R = (i)Pr, x = 0, 1b; R = (n)Pr, L = PPh(3), x = 1, 2; R = (n)Pr, L = P(n)Bu(3), x = 1, 3) as biomimetic models of the active site of Fe-only hydrogenase. The presence of this weak N...C(CO(ap)) interaction provides electronic perturbation at the Fe center. The distance of the N...C(CO(ap)) contact is 3.497 A in 1a. It increases by 0.455 A in 2 when electronic density of the Fe site is slightly enriched by a weak sigma-donating ligand, PPh(3). A longer distance (4.040 A) is observed for the P(n)Bu(3) derivative, 3. This N...C(CO(ap)) distance is thus a dynamic measure of electronic nature of the Fe(2) core. Variation of electronic richness within the Fe(2) moiety among the complexes reflects on their electrochemical response. Reduction of 2 is recorded at the potential of -2.17 V, which is 270 mV more negative than that of 1. Complex 3 requires additional 150 mV for the same reduction. Such cathodic shift results from CO substitution by phosphines. Electrocatalytic hydrogen production from HOAc by both kinds of complexes (all-CO and phosphine-substituted species) requires the potential close to that for reduction of the parent molecules in the absence of acids. The catalytic mechanism of 1a is proposed to involve proton uptake at the Fe(0)Fe(I) redox level instead of the Fe(0)Fe(0) level. This result is the first observation among the all-CO complexes with respect to electrocatalysis of HOAc.

Fe3(CO)12 reacted with azadiethylthiols afforded [Fe2(μ‐S(CH2)2NR(CH2)2S)(CO)6]2 (R = nPr, 1A; iPr, 2A). Structure analysis revealed that 1A features the anti‐(a,e,a,e) configuration, while its iso‐propyl 2A adopts the syn‐(a,e,a,e) arrangement. NMR measurements at room temperature confirmed this structure, showing distinct signals for 2 NCH2 and 2 SCH2 methylene groups. Acid treatment of 1–2 yielded N‐protonated species (1A–H, 2A–H), maintaining the anti‐(a,e,a,e) configuration. Isolation of 1B–H revealed both the syn‐(a,e,e,a) and anti‐(a,e,e,a) configuration by X‐ray single‐crystallography. Protonation of 1A–H induced downfield shifts in methylene proton signals, with NH hydrogen recorded at 6.96 ppm. Furthermore, 1B–H displays similar NMR behavior, indicating the coexistence of two isomeric molecules of 1B–H, syn‐(a,e,e,a) and anti‐(a,e,e,a), which is consistent with the crystallographic results. Moreover, ion mobility‐mass spectrometry (IM‐MS) is harnessed for the swift identification and differentiation of these isomeric complexes in solution. By leveraging accurate mass measurements and MS/MS analyses, the molecular formula and constituents are validated. The sample mobility enables straightforward characterization of 1A, 1B, and 2A in relation to their stereo‐ and regio‐configurations, obviating the need for extensive time or sample quantities. Integration of findings from X‐ray crystallography, NMR, and IM‐MS furnishes precise and comprehensive structural insights into the coordination complexes. [ABSTRACT FROM AUTHOR]

Abstract: The heterotrimetallic complexes [FeMFe(dpa)4Cl2] (M=Ni (1), Pd (2), and Pt (3); dpa−=dipyridylamido) featuring two high‐spin iron centers linked by Group 10 metals were synthesized and their physical properties were investigated. Oxidation of 1–3 with suitable oxidants in CH2Cl2 solution yielded the mixed‐valent species [1]+/2+–[3]+/2+. The solution properties of [1]0/+/2+–[3]0/+/2+ were characterized by 1H NMR and UV/Vis/NIR spectroscopy as well as spectroelectrochemisty. The mixed‐valent states of [1]+–[3]+ obtained by electrochemical or chemical oxidation are classified as class II valence delocalization. The solid‐state structures of 1–3, [1]+, [3]+, and [1]2+ were determined by single‐crystal X‐ray diffraction analysis, exhibiting a linear metal framework with an approximate D4 symmetry. The spin states and magnetic properties were studied by using SQUID magnetometry, EPR and Mössbauer spectroscopy, and DFT calculations. Antiferromagnetic interactions between terminal high‐spin iron centers are present within [1]0/+/2+–[3]0/+/2+ and the |J| values increase with the central metal ion changing from Ni to Pt. The DFT calculations reproduce the antiferromagnetic coupling and ascribe it to a σ‐type exchange pathway. The substitution of the central metal not only influences the spin–spin interactions but also the degree of electronic delocalization between the terminal iron sites along the Fe‐M‐Fe chains. [ABSTRACT FROM AUTHOR]

Biomimetic diiron complexes bearing redox non-innocent ligands are discussed in this review. The complexes are synthesized to model the active site of [FeFe] hydrogenase in order to elucidate the catalytic mechanism of H2 evolution and design superior artificial catalysts. Employment of the redox active ligands serves an important factor to modulate electronic structure of the Fe2 core as the similar functionality exerted by the [4Fe4S] cofactor within the H-cluster. Different types of redox active ligands are summarized. The influence of their ligation is observable in spectroscopy as well as cyclic voltammetry, and studied by theoretical calculation. [ABSTRACT FROM AUTHOR]

The one-electron oxidations of a Fe2 complex lead to the formation of a persistent metal-stabilized thiyl radical Fe2 species, mixed-valent Fe4, and Fe8 complexes. The unpaired spin in the Fe2 radical species delocalizes over the Fe2 and the aromatic dithiolate, mostly on the terminal sulfur. The subsequent dimerization of the singly oxidized Fe2 to the Fe4 retains the partial thiyl radical character. For an analogue with less steric hindrance, the π-π stacking interaction between the dithiolato aromatic rings induces generation of the Fe8, in which process electronic structures of the species are modulated through reducing the thiyl radical to the thiolate. Electronic reorganization repeats when the Fe8 is converted to Fe4. Electronic interplay in the complexes decreases the energy gap of frontier MOs and buffers electronic impacts upon redox events. Easier accessible redox potentials and increased stability of the species are facilitated. The results demonstrate that electronic versatility of the benzenedithiolate exerts pronounced influences on electronic and coordination structure of the metal complexes. [ABSTRACT FROM AUTHOR]