Thermodynamics of the Cu^II μ-Thiolate and Cu^I Disulfide Equilibrium: A Combined Experimental and Theoretical Study

Abstract

The redox equilibrium between dinuclear Cu(II) μ-thiolate and Cu(I) disulfide structures has been analyzed experimentally and via DFT calculations. Two new ligands, L(2)SSL(2) and L(4)SSL(4), and their Cu(II) μ-thiolate and Cu(I) disulfide complexes were synthesized. For L(2)SSL(2), these two redox-isomeric copper species are shown to be in equilibrium, which depends on both temperature and solvent. For L(4)SSL(4) the μ-thiolate species forms as the kinetic product and further evolves into the disulfide complex under thermodynamic control, which creates the unprecedented possibility to compare both species under the same reaction conditions. The energies of the μ-thiolate and disulfide complexes for two series of related ligands have been calculated with DFT; the results rationalize the experimentally observed structures, and emphasize the important role that steric requirements play in the formation of the Cu(II) thiolate structure.

Coordination of new disulfide ligands to CuI and CuII: Does a CuII μ-thiolate complex form?

“…[Cu I (CH 3 CN) 4 ](BF 4 ), L2, (3R,6S)-meso-3,6-bis(tert-butyloxycarbonylaminomethyl)-1,2-dithiacyclohexane, N-hydroxymethylpyrazole and N-hydroxymethyl-3,5-dimethylpyrazole were synthesized according to literature procedures [13,[17][18][19]. NMR spectra were recorded on a Bruker 300 DPX spectrometer.…”

“…3. The half-wave potentials (E 1/2 ) and the peak-topeak separations (DEp) of the Cu I complexes containing either L1, L2, [13] L3 or L4 are given in Table 3.…”

“…This conversion, in which Cu II is reduced to Cu I and the thiolate ligands are oxidized to form a disulfide bond, takes place intramolecularly and in some cases can be reversed in a controlled manner [11][12][13]. It has been reported that small ligand changes can determine the formation of either a Cu II l-thiolate or a Cu I disulfide complex [14].…”

“…The difference between L3 and L4 lies in the methyl groups on the pyrazole rings, as addition of a methyl group to a pyridyl moiety has shown to have a large effect on the complex formation [14]. Ligand L2 was used for comparative purposes, because of its ability to form both Cu II l-thiolate and Cu I disulfide complexes [13]. The …”

Catalytic catechol oxidation by copper complexes: development of a structure–activity relationship

“…2 were synthesized according to literature procedures or are commercially available. 4,7,8,[20][21][22][23][24] As the ligands are similar to each other, they were systematically named by their structure. For example L 1 stands for the fragment N,N-bis(2-pyridylmethyl)aminoethyl and Py for 2-pyridylmethyl.…”