Oxidative stannylation with K6Sn2Se6/SnCl2: Synthesis and crystal structures of SnCl3-substituted pseudo-tetrahedral cobalt(III) complexes

The ternary Zintl phase K6Sn2Se6 was recently shown to mildly oxidize Cp*-l igated Co-II complexes, although Sn in the formal +III oxidation state usua lly tends to be a reducing species. Depending on the reaction conditions, d ifferent ratios of Co-II and Co-III were observed within the product molecu les. Cyclovoltammetric investigations indicated that reversible electron tr ansfer occurred between some of the isolated molecules synthesized that way . In order to study the redox behavior of the oxidizing Sn-III species in t he reaction system, large excesses of Sn-II were added to the solvent THF. A suppression of the Co-II --> Co-III transition was expected if the oxidat ion was reversible. Herein we report the synthesis and crystal structures o f [Co-2(mu-Cl)(3)(thf)(6)][CoClCp*(SnCl3)(2)] (1) and [Li(thf)(4)][CoCp*(Sn Cl3)(3)] (2) formed from reactions of [CoClCp*](2) with K6Sn2Se6 in the pre sence of SnCl2 in THE The results show that oxidation could not be inhibite d, indicative of irreversible redox mechanisms. Additionally, one observes the formal insertion of SnCl2 units in Co-Cl bonds. For completion of the 1 8-electron configuration, the Cp*Co-III 14-electron fragment forms sterical ly strained anionic structures that may in the future be relevanct as precu rsors for the formation of Cp*Co-coated heteroatomic aggregates. Furthermor e, the cation in 1 is one of the few examples of threefold mu(2)-bridged bi nuclear Co-II complexes.