Reaction of β-diketiminate copper(II) complexes and Na2S2 resulted in formation of (μ-η2:η2-disulfido)dicopper(II) complexes (adduct formation) or β-diketiminate copper(I) complexes (reduction of copper(II)) depending on the substituents of the supporting ligands. In the case of sterically less demanding ligands, adduct formation occurred to provide the (μ-η2:η2-disulfido)dicopper(II) complexes, whereas reduction of copper(II) took place to give the corresponding copper(I) complexes with sterically more demanding β-diketiminate ligands. Spectroscopic examinations of the reactions at low temperature using UV-vis and ESR as well as kinetic analysis have suggested that a 1 : 1 adduct LCuII–S–SNa with an end-on binding mode is initially formed as a common intermediate, from which different reaction pathways exist depending on the steric environment of the metal-coordination sphere provided by the ligands. Thus, with the sterically less demanding ligands, rearrangement of the disulfide adduct from end-on to side-on followed by self-dimerisation occurs to give the (μ-η2:η2-disulfido)dicopper(II) complexes, whereas such an intramolecular rearrangement of the disulfide co-ligand does not take place with the sterically more demanding ligands. In this case, homolytic cleavage of the CuII–S bond occurs to give the reduced copper(I) product. The steric effects of the supporting ligands have been discussed on the basis of detailed analysis of the crystal structures of the copper(II) starting materials.
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