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

Abstract

Diiron bis(monothiolato)-bridged hydrogenase mimics [Fe 2 (μ-S i Pr) 2 (CO) 6 ] A ( i Pr = isopropyl) and their phosphine derivatives [Fe 2 (μ-S i Pr) 2 (CO) 5 (L 1/2 )] and [Fe 2 (μ-S i Pr) 2 (CO) 4 (L 3 )] {tricyclohexylphosphine (L 1 , PCy 3 ) 1, triphenylphosphine (L 2 , PPh 3 ) 2 and cis-1,2-bis(diphenylphosphino)ethylene (L 3 , dppv) 3} have been synthesized and investigated for electrocatalytic proton reduction activity in CH 3 CNÀ H 2 O. Based on the FTIR data (red-shift), the electron-donating ability of the phosphines followed the order: dppv > PCy 3 > PPh 3 (average shift value with respect to complex A was 61 (1), 51 (2) and 80 (3) cm À 1 ). From CV measurements, it was seen that the catalytic reduction potential (acetic acid as proton source) shifted considerably towards positive potentials (anodic shift) on changing the solvent from pure CH 3 CN to CH 3 CNÀ H 2 O (4 : 1 v/v). An increase in the percentage of water in CH 3 CN led to the decomposition of complexes 1 and 3. Though complexes A and 2 were stable in CH 3 CNÀ H 2 O (3 : 2 v/v), no improvement in electrocatalytic currents was observed.

Design of Rigidified μ-(9-Fluorenethiolate) {FeFe} Hydrogen Evolving Catalysts

“…Since the “plateau” region was not observed, the value of the observed rate constant k obs ( k obs = k [H + ] 2 ) approximated at 189 mM of CH 3 COOH was 414 s –1 (eq ). , Also, higher i cat / i p and TOF values for complex 1 indicate that 1 was a more efficient catalyst in comparison to similar reported diiron hexacarbonyl monothiolate-bridged complexes [Fe 2 (μ-S i Pr) 2 (CO) 6 ] ( D ; i Pr = isopropyl) and [Fe 2 (μ-7-mercapto-4-methylcoumarin) 2 (CO) 6 ] E (Table ). i normalc normala normalt i normalp = n 0.4463 R T k o b s F ν n is the number of electrons required to generate 1 mol of H 2 (here, n = 2), F is the Faraday constant, ν is the scan rate in V s –1 , R is the ideal gas constant, T is the temperature in kelvin, and k obs is the observed rate constant in s –1 .…”

“…Since the "plateau" region was not observed, the value of the observed rate constant k obs (k obs = k[H + ] 2 ) approximated at 189 mM of CH 3 COOH was 414 s −1 (eq 3). 42,43 Also, higher i cat /i p and TOF values for complex 1 indicate that 1 was a more efficient catalyst in comparison to similar diiron hexacarbonyl monothiolate-bridged complexes [Fe 2 (μ-S i Pr) 2 (CO) 6 ] (D; i Pr = isopropyl) 44 and [Fe 2 (μ-7-mercapto-4-methylcoumarin) 2 (CO) 6 ] E 32 (Table 1).…”

Improved Access to ‘Butterfly’ Di‐Iron Dithiolates Fe2(μ‐SR)2(CO)6 and their Mono‐ and Bis(phosphine) Adducts

“…The metrical parameters for the set of structures are in accord with previous reports [7,30–34] and are available as Supporting Information. The steric effect of phosphine substitution largely forces the complexes to the syn ‐geometry, the only exceptions being 4c Me and 4c Et .…”

“…Moving to the synthesis of mono-PCy 3 substituted derivatives, treatment of 1 Me , 1 Et , 1 iPr , 1 tBu , 1 Ph and 1 Bn with one equivalent of PCy 3 under reflux give the corresponding monosubstituted complexes Fe 2 (μ-SR) 2 (PCy 3 )(CO) 5 (4 b), 31 P{ 1 H} NMR spectra in CDCl 3 showed singlet signals for the bound phosphine in the range 55-66 ppm. The equivalent mono-PPh 3 complexes 4 c could also be accessed by refluxing the starting materials in a 1 : 1 ratio.…”