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

The Ph3PAu+ cation, renowned as an isolobal analogue of H+, was found to serve as a proton surrogate and form a stable Au2Fe2 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 SAu 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]H2ase-active-site biomimetic [(μ2-SCH2(NR)CH2S){Fe(CO)3}2].