Oxidative Stannylation with K6Sn2Se6/SnCl2: Synthesis and Crystal Structures of SnCl3-Substitutedpseudo-Tetrahedral Cobalt(III) Complexes

Abstract

The ternary Zintl phase K6Sn2Se6 was recently shown to mildly oxidize Cp*-ligated CoII complexes, although Sn in the formal +III oxidation state usually tends to be a reducing species. Depending on the reaction conditions, different ratios of CoII and CoIII were observed within the product molecules. Cyclovoltammetric investigations indicated that reversible electron transfer occurred between some of the isolated molecules synthesized that way. In order to study the redox behavior of the oxidizing SnIII species in the reaction system, large excesses of SnII were added to the solvent THF. A suppression of the CoII → CoIII transition was expected if the oxidation was reversible. Herein we report the synthesis and crystal structures of [Co2(μ-Cl)3(thf)6][CoClCp*(SnCl3)2] (1) and [Li(thf)4][CoCp*(SnCl3)3] (2) formed from reactions of [CoClCp*]2 with K6Sn2Se6 in the presence of SnCl2 in THF. The results show that oxidation could not be inhibited, indicative of irreversible redox mechanisms. Additionally, one observes the formal insertion of SnCl2 units in Co−Cl bonds. For completion of the 18-electron configuration, the Cp*CoIII 14-electron fragment forms sterically strained anionic structures that may in the future be relevanct as precursors for the formation of Cp*Co-coated heteroatomic aggregates. Furthermore, the cation in 1 is one of the few examples of threefold µ2-bridged binuclear CoII complexes.