Effects of Alkane Linker Length and Chalcogen Character in [FeFe]-Hydrogenase Inspired Compounds

Di-, tri- and tetraphosphine-substituted Fe/Se carbonyls: Synthesis, Characterization and electrochemical properties

The active sites of [FeFe]-hydrogenase promoted by Fe/E (E=S, Se) clusters have attracted considerable interest due to their significance for understanding the interconversion of hydrogen with protons and electrons. As...

Electronic Communication between Dithiolato-Bridged Diiron Carbonyl and S-Bridged Redox-Active Centres

The catalytic potential of linked redox centres is exemplified by the catalytic site of [FeFe]-hydrogenases, which feature a diiron subsite linked by a cysteinyl S atom to a 4Fe4S cube. The investigation of systems possessing similarly-linked redox sites is important because it provides a context for understanding the biological system and the rational design of abiological catalysts. The structural, electrochemical and spectroscopic properties of Fe2(CO)5(CH3C(CH2S)2CH2SPhNO2, I-bzNO2 and the aniline analogue, I-bzNH2, are described and IR spectroelectrochemical studies have allowed investigation of the reduction products and their reactions with CO and protons. These measurements have allowed identification of the nitrobenzenyl radical anion, quantification of the shifts of the (CO) bands on ligand-based reduction compared with NO2/NH2 exchange and protonation of the pendent ligand. The strength of thioether coordination is related to the electronic effects, where competitive binding studies with CO show that CO/thioether exchange can be initiated by redox processes of the pendent ligand. Stoichiometric multi electron/proton transfer reactions of I-bzNO2 localised on nitrobenzene reductions occur at mild potentials and a metal-centred reduction in the presence of protons does not lead to significant electrocatalytic proton reduction.

FeMo Heterobimetallic Dithiolate Complexes: Investigation of Their Electron Transfer Chemistry and Reactivity toward Acids, a Density Functional Theory Rationalization

The electrochemical behavior of complexes [FeMo(CO)₅(κ²-dppe)(μ-pdt)] (1) and [FeMo(CO)₄(MeCN)(κ²-dppe)(μ-pdt)] (2), in the absence and in the presence of acid, has been investigated. The reduction of 1 follows at slow scan rates, in CH₂Cl₂-[NBu₄][PF₆] and acid-free media, an EC_revE mechanism that is supported by cyclic voltammetry (CV) experiments and digital CV simulations. In MeCN-[NBu₄][PF₆], the electrochemical reduction of 1 is the same as in dichloromethane and follows an ECE mechanism at slow scan rates, but with a positive shift of the redox potentials. In contrast, the oxidation of 1 is strongly solvent-dependent. In dichloromethane, the oxidation of 1 is reversible and involves a single electron, while in acetonitrile, it is irreversible at moderate and slow scan rates ( v ≤ ca. 1 V s^-1), and some chemical reversibility is apparent at higher scan rates ( v = 10 V s^-1). Density functional theory calculations revealed that the chemical step in the EC_revE mechanism corresponds to the dissociation of one PPh₂ end of the diphosphine ligand and the transfer of the semibridging CO to the Fe atom, similarly to the mechanism observed in the FeFe analogue complex. However, in the case of 1, the subsequent coordination of the phosphine ligand to the other metal is an unfavorable process.

[FeFe]-Hydrogenase H-Cluster Mimics with Various -S(CH2)nS- Linker Lengths (n = 2-8): A Systematic Study

The effect of the nature of the dithiolato ligand on the physical and electrochemical properties of synthetic H-cluster mimics of the [FeFe]-hydrogenase is still of significant concern. In this report we describe the cyclization of various alkanedithiols to afford cyclic disulfide, tetrasulfide, and hexasulfide compounds. The latter compounds were used as proligands for the synthesis of a series of [FeFe]-hydrogenase H-cluster mimics having the general formulas [Fe₂(CO)₆{μ-S(CH₂)_nS}] (n = 4-8), [Fe₂(CO)₆{μ-S(CH₂)_nS}]₂ (n = 6-8), and [Fe₂(CO)₆{(μ-S(CH₂)_nS)₂}] (n = 6-8). The resulting complexes were characterized by ¹H and ¹³C{¹H} NMR and IR spectroscopic techniques, mass spectrometry, and elemental analysis as well as X-ray analysis. The purpose of this research was to study the influence of the systematic increase of n from 2 to 7 on the redox potentials of the models and the catalytic ability in the presence of acetic acid (AcOH) by applying cyclic voltammetry.

Steric effect of the dithiolato linker on the reduction mechanism of [Fe2(CO)6{μ-(XCH2)2CRR′}] hydrogenase models (X = S, Se)

Investigations of the electrochemical properties of [Fe₂(CO)₆{μ-(XCH₂)₂CRR′}] (X = S, Se; R or R′ = H or Me) showed that the complex with the bulkiest CMe₂moiety undergoes reduction with potential inversion.