Disulfide Versus Diselenide Complexes of Copper: Air-Free and Air-Exposed Syntheses Result in Variable Ligands and Coordination

Reactions of bis(1-methylimidazole-2)disulfide (MMI^DS) or bis(1-methylimidazole-2)diselenide (MMI^DSe) with Cu(I) result in a variety of products depending on conditions. Under air-free conditions, dinuclear complexes [Cu₂(µ,κ^S-MMI)₂(κ^N,N’-MMI^DS)₂][BF₄]₂ and [Cu₂(µ,κ^Se-MMI^Se)₂(κ^N,N’-MMI^DSe)₂][BF₄]₂ were obtained and structurally characterized. Both complexes show reduction of the MMI^DS or MMI^DSe and subsequent bridging of the thione or selone between the dinuclear Cu(I) centers. Combining MMI^DSe with Cu(I) in air resulted in crystallization of three different complexes from the same reaction mixture, as confirmed by X-ray crystallography. The various products, [Cu(κ^N,N’-MMI^MSe)(κ^N,N’-MMI^TSe)(CH₃CN)][BF₄]₂, [Cu(κ^N,N’-MMI^Se-CH₂-MMI^Se)₂[BF₄]₂, and the co-crystallized [[Cu(κ^N,N’-MMI^DSe)₂][Cu(κ^N,N’-MMI^Se-CH₂-MMI^Se)][BF₄]₄, indicate that significant reactivity occurs with the availability of air and CH₂Cl₂ solvent. In addition to oxidation of Cu(I) to Cu(II), the MMI^DSe ligands also react to form monoselenide, triselenide, and Se-CH₂-Se bridged selenide ligands.

Graphical Abstract

Although Cu(I) reactions with bis(1-methylimidazole-2)disulfide (MMI^DS) or bis(1-methylimidazole-2)diselenide (MMI^DSe) under air-free conditions result in formation of [Cu₂(µ,κ^S-MMI)₂(κ^N,N’-MMI^DS)₂][BF₄]₂ and [Cu₂(µ,κ^Se-MMI^Se)₂(κ^N,N’-MMI^DSe)₂][BF₄]₂, respectively, treating MMI^DSe with Cu(I) in air results in crystallization of three different complexes from the same reaction mixture: [Cu(κ^N,N’-MMI^MSe)( κ^N,N’-MMI^TSe)(CH₃CN)][BF₄]₂, [Cu(κ^N,N’-MMI^Se-CH₂-MMI^Se)₂[BF₄]₂, and the co-crystallized [[Cu(κ^N,N’-MMI^DSe)₂][Cu(κ^N,N’-MMI^Se-CH₂-MMI^Se)][BF₄]₄, indicating that significant reactivity occurs with the availability of air and CH₂Cl₂ solvent.