A reduced 2Fe2S cluster probe of sulfur-hydrogen versus sulfur-gold interactions

Abstract

The Ph3 PAu(+) cation, renowned as an isolobal analogue of H(+) , was found to serve as a proton surrogate and form a stable Au2 Fe2 complex, [(μ-SAuPPh3 )2 {Fe(CO)3 }2 ], analogous to the highly reactive dihydrosulfide [(μ-SH)2 {Fe(CO)3 }2 ]. Solid-state X-ray diffraction analysis found the two SAuPPh3 and SH bridges in anti configurations. VT NMR studies, supported by DFT computations, confirmed substantial barriers of approximately 25 kcal mol(-1) to intramolecular interconversion between the three stereoisomers of [(μ-SH)2 {Fe(CO)3 }2 ]. In contrast, the largely dative SAu bond in μ-SAuPPh3 facilitates inversion at S and accounts for the facile equilibration of the SAuPPh3 units, with an energy barrier half that of the SH analogue. The reactivity of the gold-protected sulfur atoms of [(μ-SAuPPh3 )2 {Fe(CO)3 }2 ] was accessed by release of the gold ligand with a strong acid to generate the [(μ-SH)2 {Fe(CO)3 }2 ] precursor of the [FeFe]H2 ase-active-site biomimetic [(μ2 -SCH2 (NR)CH2 S){Fe(CO)3 }2 ].

Keywords: hydrogenases; hydrosulfides; iron-sulfur-gold clusters; isolobal species; sulfur inversion.