Insights into the Two‐Electron Reductive Process of [FeFe]H₂ase Biomimetics: Cyclic Voltammetry and DFT Investigation on Chelate Control of Redox Properties of [Fe₂(CO)₄(κ²‐Chelate)(μ‐Dithiolate)]

Abstract

The electrochemical reduction of complexes [Fe 2 (CO) 4 (k 2-phen)(m-xdt)] (phen = 1,10-phenanthroline;x dt = pdt (1), adt iPr (2)) in MeCN-[Bu 4 N][PF 6 ]0 .2 m is described as a two-reduction process. DFT calculations show that 1 and its monoreduced form 1 À À display metal-and phenanthrolinecentered frontier orbitals (LUMO and SOMO) indicating the non-innocenceo ft he phenanthroline ligand.T wo energetically close geometries were found for the doubly reduced species suggesting an intriguing influence of the phenanthroline ligand leading to the cleavage of aF e ÀSb ond as proposed generally for this type of complex or retaining the electrond ensity and avoiding FeÀSc leavage. Extension of calculations to other complexes with edt, adt iPr bridge and even virtuals pecies [Fe 2 (CO) 4 (k 2-phen)(m-adt R)] (R = CH(CF 3) 2 , H) or [Fe 2 (CO) 4 (k 2-phen)(m-pdt R)] (R = CH(CF 3) 2 , iPr) showed that the relative stabilityb etween both two-electron-reduced isomersd epends on the nature of the bridge andt he possibility to establish ar emote anagostic interaction between the iron center{ Fe(CO) 3 }a nd the group carried by the bridged-head atom of the dithiolate group. Scheme1.(a) Schematic view of the H-cluster of [FeFe]hydrogenases, (b) and (c) two representative exampleso fd iiron complexes featuringr edoxactive ligand.

Toward Diiron Dithiolato Biomimetics with Rotated Conformation of the [FeFe]‐Hydrogenase Active Site: A DFT Case Study on Electron‐Rich, Isocyanide‐Based Scaffolds

“…This observation is reasonable in electron‐rich systems where a strong CT from the unrotated unit to the rotated one occurs: indeed the rotated Fe receiving electron density from the unrotated one is preferentially stabilized by a long range interaction with a relatively acidic H δ+ rather than with the nitrogen lone pair. This result is in line with recent theoretical predictions on Fe 2 S 2 biomimics, revealing a strong influence of the polarization of the dithiolato bridgehead in stabilizing the rotated Fe upon reduction i. e. upon increasing electron density in the system [62] . However, this intramolecular stabilizing interaction is presumably too weak to compensate for the rotation energy cost, and the predicted ΔG R is positive (4.5 kcal/mol).…”

“…This result is in line with recent theoretical predictions on Fe 2 S 2 biomimics, revealing a strong influence of the polarization of the dithiolato bridgehead in stabilizing the rotated Fe upon reduction i. e. upon increasing electron density in the system. [62] However, this intramolecular stabilizing interaction is presumably too weak to compensate for the rotation energy cost, and the predicted ΔG R is positive (4.5 kcal/ mol). Another factor contributing to destabilizing the rotated form is the presence of a H-bond between the axial NÀ H group and MeNC nitrogen, which in fact stabilized the unrotated isomer.…”

Use of the Asymmetrical Chelating N-Donor 2-Imino-Pyridine as a Redox [Fe4S4] Cubane Surrogate at a Di-Iron Site Related to [FeFe]-Hydrogenases

“…In this context, various redox ligands were combined with bio-inspired di-iron systems, in the hope that they could act as redox electron-reservoirs with non-innocent properties [11][12][13][14] as [Fe4S4], allowing a catalytic activity. Among these ligands, are included in particular chelating nitrogen donor ligands, such as 2,2 -bipyridine (bipy), 1,10-phenanthroline (phen), 2,2 -bipyrimidine (bpym), 2-(phenylazo)pyridine (pap) (Scheme 1b) [15][16][17][18][19][20][21][22]. In parallel, diphosphines such as bma (bma = 2,3-bis(diphenylphosphino)maleic anhydride), dppen (1,2-bis(diphenylphosphino)ethene), bpcd (4,5-bis(diphenylphosphino)-4-cyclopenten-1,3dione), were combined with di-iron systems, but it was shown that they act as innocent bystanders when they are associated with di-iron {Fe 2 (CO) 4 (µ-dithiolate)} core [23][24][25].…”

Synthesis, Characterization and Electrochemical Studies of bis(Monothiolato) {FeFe} Complexes [Fe2(μ‐SC6H4‐OMe‐m)2(CO)5L] (L = CO, PCy3, PPh3)

“…Furthermore, most of the studies have considered mainly dithiolates as the linkers [1,19–50] . Only recently, the focus has shifted to monothiolate‐based {FeFe} systems.…”