Reactions of Rh2(CH3COO)4with thiols and thiolates: a structural study

Abstract

The structural differences between the aerobic reaction products of Rh2(AcO)4(1; AcO−= CH3COO−) with thiols and thiolates in non-aqueous media are probed by X-ray absorption spectroscopy. For this study, ethanethiol, dihydrolipoic acid (DHLA; a dithiol) and their sodium thiolate salts were used. Coordination of simple thiols to the axial positions of Rh2(AcO)4with Rh—SH bonds of 2.5–2.6 Å keeps the RhII—RhIIbond intact (2.41 ± 0.02 Å) but leads to a colour change from emerald green to burgundy. Time-dependent density functional theory (TD-DFT) calculations were performed to explain the observed shifts in the electronic (UV–vis) absorption spectra. The corresponding sodium thiolates, however, break up the Rh2(AcO)4framework in the presence of O2to form an oligomeric chain of triply S-bridged Rh(III) ions, each with six Rh—S (2.36 ± 0.02 Å) bonds. The RhIII...RhIIIdistance, 3.18 ± 0.02 Å, in the chain is similar to that previously found for the aerobic reaction product from aqueous solutions of Rh2(AcO)4and glutathione (H3A), {Na2[Rh2III(HA)4]·7H2O}n, in which each Rh(III) ion is surrounded by about four Rh—S (2.33 ± 0.02 Å) and about two Rh—O (2.08 ± 0.02 Å). The reaction products obtained in this study can be used to predict how dirhodium(II) tetracarboxylates would react with cysteine-rich proteins and peptides, such as metallothioneins.