On the structure of a proposed mixed-valent analogue of the diiron subsite of [FeFe]-hydrogenase.

We show that a dinuclear assembly apparently providing the first example of a synthetic molecule exhibiting key features of the diiron subsite of [FeFe] hydrogenase, viz. CO-bridging of a coordinatively unsaturated, dithiolate-bridged mixed-valence diiron centre, is in fact a diamagnetic tetranuclear complex.

Modeling [Fe-Fe] hydrogenase: evidence for bridging carbonyl and distal iron coordination vacancy in an electrocatalytically competent proton reduction by an iron thiolate assembly that operates through Fe(0)-Fe(II) levels.

IR spectroelectrochemistry of Fe4{Me(CH2S)3}2(CO)8 (4Fe6S) in the nu(CO) region shows that the neutral and anion forms have all their CO groups terminally bound to the Fe atoms; however, for the dianion there is a switch of the coordination mode of at least one of the CO groups. The available structural and nu(CO) spectra are closely reproduced by density-functional theory calculations. The calculated structure of 4Fe6S2- closely mirrors that of the diiron subsite of the [Fe-Fe] hydrogenase H cluster with a bridging CO group and an open coordination site on the outer Fe atom of pairs of dithiolate-bridged Fe0FeII subunits connected by two bridging thiolates.

Assignment of molecular structures to the electrochemical reduction products of diiron compounds related to [Fe-Fe] hydrogenase: a combined experimental and density functional theory study.

The reduction chemistry of (mu-bridge)[Fe(CO)3]2 [bridge = propane-1,3-dithiolate (1) and ethane-1,2-dithiolate (2)] is punctuated by the formation of distinct products, resulting in a marked difference in CO inhibition of electrocatalytic proton reduction. The products formed following reduction of 2 have been examined by a range of electrochemical, spectroelectrochemical, and spectroscopic approaches. Density functional theory has allowed assessment of the relative energies of the structures proposed for the reduction products and agreement between the calculated spectra (IR and NMR) and bond distances with the experimental spectra and EXAFS-derived structural parameters.

Steps along the path to dihydrogen activation at [FeFe] hydrogenase structural models: dependence of the core geometry on electrocatalytic proton reduction.

Differences in the rate of electrocatalytic proton reduction by Fe2(mu-PPh2)2(CO)6, DP, and the linked phosphido-bridged analogue Fe2(mu,mu-PPh(CH2)3PPh)(CO)6, 3P, suggest that dihydrogen elimination proceeds through a bridging hydride. The reaction path was examined using electrochemical, spectroscopic, and in silico studies where reduction of 3P gives a moderately stable monoanion [Kdisp(3P-) = 13] and a distorted dianion. The monomeric formulation of 3P- is supported by the form of the IR and EPR spectra.

Electron transfer at a dithiolate-bridged diiron assembly: electrocatalytic hydrogen evolution.

Electrochemical reduction of Fe(2)(mu-pdt)(CO)(6) 1 (pdt = propane-1,3-dithiolate) leads initially to a short-lived species, 1-, then subsequently to two-electron reduced products, including a CO-bridged diiron compound, 1B. The assignment of the redox level of 1- is based on EPR and UV-vis spectra together with the observation that a CO-saturated solution of 1- decays to give 1 and 1B. Hydride reduction of 1 also results in formation of 1B via a relatively long-lived formyl species, 1(formyl).

Electrocatalytic proton reduction by phosphido-bridged diiron carbonyl compounds: distant relations to the H-cluster?

Intermediates formed during reduction of Fe(2)(mu-PPh(2))(2)(CO)(6) (1) in the presence of protons have been identified by spectroelectrochemical, continuous-flow, and interrupted-flow techniques. The mechanism for electrocatalytic proton reduction suggested by these observations yields digital simulation of the voltammetry in close agreement with measurements conducted in THF over a range of acid concentrations. The mechanism for electrocatalytic proton reduction involves initial formation of the dianion, 1(2-), which is doubly protonated prior to further reduction and dihydrogen elimination.

Transient FTIR spectroelectrochemical and stopped-flow detection of a mixed valence (Fe(I)-Fe(II)) bridging carbonyl intermediate with structural elements and spectroscopic characteristics of the di-iron sub-site of all-iron hydrogenase.

Iron(I) in biology?: one-electron oxidation of an (Fe(I)-Fe(I)) carbonyl cyanide precursor bearing a proximal thioether group leads to an (Fe(I)-Fe(II)) bridging carbonyl transient with spectral features similar to the di-iron sub-site of the CO inhibited paramagnetic centre of all-iron hydrogenase.