Electrochemical catalysis investigation into the dynamic coordination properties of a pyridine-substituted [2Fe2S] model complex

Abstract

A pyridine-substituted diiron dithiolate complex (μ-dmedt)Fe2(CO)5Py 1 was prepared as a biomimetic model for the active site of [FeFe]-hydrogenase by CO-substitution of all-carbonyl complex (μ-dmedt)Fe2(CO)6 [dmedt = SCH(CH3)CH(CH3)S] with pyridine, which has been determined by IR, 1 HNMR, elemental analysis and X-ray crystallography analysis. Electrochemical and IR investigation of the complex 1 in MeCN-[NBu4][PF6] under N2 and under CO has demonstrated that the reversible transformation reaction between the complex 1 and the acetonitrile-substituted species (μ-dmedt)Fe2(CO)5(NCCH3) 2. As in reverse transformation, a 1

[FeFe] Hydrogenase: 2‐Propanethiolato‐Bridged {FeFe} Systems as Electrocatalysts for Hydrogen Production in Acetonitrile‐Water

“…The carboxylate‐substituted diiron‐adt complexes [Fe 2 ((μ‐SCH 2 ) 2 N(R))(CO) 6‐x L x ] (R=−(CH 2 ) 3 COOH or −CH(CH 2 CH 3 )(COOH), L=PMe 3 and x=0 or 2) were electrochemically active in pure CH 3 CN with water as the proton source, likely due to hydrogen bonding interactions [9] . Similar activity in absence of acid has also been reported for complexes [Fe 2 (μ‐dmedt)(CO) 5 L] (dmedt=2,3‐butanedithiol, L=pyridine or 4,4′‐bipyridine) and [Fe 2 (μ‐SCH(CH 2 CH 3 )CH 2 S‐)(CO) 5 L] (L=PMe 3 or P(OMe) 3 ) [11,12,14] . Diiron‐bdt‐based complexes with tris( m ‐pyridyl)phosphane or dipyridylphosphole ligands functioned as HER catalysts in dilute H 2 SO 4 solution [10,13] .…”

“…[6][7][8] Since, water can function both as the solvent medium and/or proton source, and influence the overvoltage for the proton reduction process, it is highly desired to design HER (Hydrogen Evolution Reaction) catalysts that can reduce protons in aqueous media and hence, could assist in developing newer, better and efficient watersplitting systems. [9][10][11][12][13][14] Based on literature reports, water solubility of the [FeFe] H 2 ase models can be enhanced, either by incorporating a hydrophilic group in the [2Fe-2S] core or encapsulating the mimics into water-soluble structures like cyclodextrins, micelles or phospholipid vesicles. Various types of systems that are functional in aqueous media include: (i) complexes with water-solubilizing groups like 1,3-disulfanyl-2-propyltetra-O-acetyl-β-D-glucopyranoside unit on the sulfur bridgehead of the dithiolate linker; [15] (ii) peptide-based polar diiron complexes; [16,17] (iii) diiron carbonyl metallopolymer PDMAEMAg-[2Fe-2S] (DMAEMA = 2-(dimethylamino) ethyl methacrylate) with a polymer backbone along its thiolate substituent (pH 7, TOF of 250000 s À 1 and TON of 4 � 2 × 10 4 molecules of H 2 per catalytic site, operational lifetime of six days under both aerobic and anaerobic conditions); [18][19][20][21] (iv) Na + [Fe 2 (μ-SCH 2 N-(C 6 H 4 SO 3 À )CH 2 S-)(CO) 6 ] and Na + [Fe 2 (μ-SCH 2 N(C 6 H 4 SO 3 À )CH 2 S-)(CO) 5 L] (L = P(OMe) 3 , PTA and PPh 3 ) hosted in cyclodextrin (CyD); [22,23] (v) complexes [Fe 2 (μ-bdt)(CO) 6 ] (TOF, 2600 s À 1 at pH 3) and [Fe 2 (μ-bdt)(CO) 4 (P(OMe) 3 ) 2 ] (TOF, 4400 s À 1 at pH 3) dispersed into micelles of aqueous sodium dodecyl sulfate (SDS) solution; [24][25][26] (vi) complex [Fe 2 (μ,k 2 -bdt-Me)(CO) 5 (μ-PPh 2 )] embedded into bilayer vesicles (liposomes) and immobilized on carbon black without the use of anchoring groups that catalyzed H 2 production in Na 2 SO 4 (aq) solution (pH 7, η 0.4 V).…”

“…[9] Similar activity in absence of acid has also been reported for complexes [Fe 2 (μ-dmedt)(CO) 5 L] (dmedt = 2,3-butanedithiol, L = pyridine or 4,4'-bipyridine) and [Fe 2 (μ-SCH(CH 2 CH 3 )CH 2 S-)(CO) 5 L] (L = PMe 3 or P(OMe) 3 ). [11,12,14] Diiron-bdt-based complexes with tris(m-pyridyl)phosphane or dipyridylphosphole ligands functioned as HER catalysts in dilute H 2 SO 4 solution. [10,13] The protonation of pyridyl moiety allowed such complexes to solubilize in acidic aqueous media.…”

“…Only a few diiron thiolate‐bridged complexes have been studied in purely aqueous medium or in a mixture of water/organic solvent (with or without acid); the major limitation being insolubility and instability of the systems in water [6–8] . Since, water can function both as the solvent medium and/or proton source, and influence the overvoltage for the proton reduction process, it is highly desired to design HER (Hydrogen Evolution Reaction) catalysts that can reduce protons in aqueous media and hence, could assist in developing newer, better and efficient water‐splitting systems [9–14] …”