Intramolecular stabilization of a catalytic [FeFe]-hydrogenase mimic investigated by experiment and theory

Abstract

The mono-substituted complex [Fe2(CO)5(μ-naphthalene-2-thiolate)2(P(PhOMe-p)3)] was prepared taking after the structural principles from both [NiFe] and [FeFe]-hydrogenase enzymes. Crystal structures are reported for this complex and the all carbonyl analogue. The bridging naphthalene thiolates resemble μ-bridging cysteine amino acids. One of the naphthyl moieties forms π-π stacking interactions with the terminal bulky phosphine ligand in the crystal structure and in calculations. This interaction stabilizes the reduced and protonated forms during electrocatalytic proton reduction in the presence of acetic acid and hinders the rotation of the phosphine ligand. The intramolecular π-π stabilization, the electrochemistry and the mechanism of the hydrogen evolution reaction were investigated using computational approaches.

Switching Site Reactivity in Hydrogenase Model Systems by Introducing a Pendant Amine Ligand

“…Likewise, the center-to-center distance between the bridging aromatic Mebdt ligand and aromatic rings of tris­(4-methoxyphenyl)­phosphine ligand varies between 3.43 Å in 1FeH – (strong stabilizing effect, one Fe–S bond broken, iron atom protonated) and 3.74 Å in 1FeHSH (weak stabilization enabling release of H 2 ) (Figure S14, see SI). A similar stabilizing effect by a bridging aromatic thiolate and a terminal aromatic ring of the phosphine substituent was also observed in an earlier report by our group . An EECC mechanism with two consecutive one-electron steps to give 1 2– (with Gibbs free energy changes of −140 kcal/mol for BP86 and −123 kcal/mol for B3LYP) and two sequential steps of protonation also appears feasible since protonation will be facile and swift then (Scheme S2, see SI).…”

“…Incorporation of a basic terminal nitrogen-containing ligand can assist proton transfer to the nearest metal ion . When introducing larger bridging aromatic thiolate ligands , and/or terminal nitrogen-containing ligands, , a pronounced effect on redox potential and a catalyst stabilization by π–π stacking of the bridging and a terminal aromate can be seen …”

Mechanism of Diiron Hydrogenase Complexes Controlled by Nature of Bridging Dithiolate Ligand

“…[32,33] The bridging di-thiolates play an important role in the development of the biomimetic chemistry of [FeFe] hydrogenase. [34][35][36][37] Here, we extend previous work on propane dithiolate (pdt)-bridged di-nuclear iron-sulfur complexes [38][39][40] with terminal mono-or di-substituted tris(4-methoxyphenyl)phosphine (P(PhOMe-p) 3 ) ligands. The introduction of an aromatic benzene di-thiolate (bdt) allows the detailed investigation of the effects of the terminal phosphines and the nature of the μ-bridging ligands on complex stability and catalytic performance.…”

“…In model complexes, terminal phosphine ligands are good substitutes for naturally occurring CN − [32,33] . The bridging di‐thiolates play an important role in the development of the biomimetic chemistry of [FeFe] hydrogenase [34–37] . Here, we extend previous work on propane dithiolate (pdt)‐bridged di‐nuclear iron‐sulfur complexes [38–40] with terminal mono‐ or di‐substituted tris(4‐methoxyphenyl)phosphine (P(PhOMe‐ p ) 3 ) ligands.…”

[FeFe]‐hydrogenase H‐cluster mimics mediated by mixed (S, Se) and (S, Te) bridging moieties: Insight into molecular structures and electrochemical characteristics

“…The addition of one equivalent AcOH to solutions of complexes 1 and 2 causes a shift in their reduction peaks to less negative potentials by approximately 40 and 30 mV, respectively (Figure ). This anodic shift suggests that there is an interaction between the acid and the reduced species of these complexes in CH 2 Cl 2 . However, the current is not increasing with consecutive additions of AcOH indicating that catalysis is not occurred at this potential.…”