Redox Convergent Synthesis and Reactivity of a Cobalt(III)-Pentasulfido Compound

A new mononuclear cobalt(III)-pentasulfido compound, [(L)Co(S-5)] (3) has been synthesized by using a convergent redox reaction between elemental sulfur and two new cobalt(II)-thiolato compounds, [(L)Co(SR)] (R=Ph, 2 a; 2,6-Me-2-C6H4, 2 b), which in turn were synthesized from a dimeric cobalt(II) complex, [(L)(2)Co-2](2+) (1). Compound 3 features a low-spin, diamagnetic, Co(III) center with a coordinated pentasulfido (S-5(2-)) chain and has no precedence in the literature. Compound 3 is highly stable towards reduction with a potential of -1.36 V (vs. Cp2Fe+/Cp2Fe) and gives back 1 upon chemical/electrochemical reduction. Reaction of 3 with phosphines yields back 1 and phosphine sulfides, while protonation of the coordinated S-5(2-) chain in 3 leads to the formation of 1, elemental sulfur and H2S. Finally, transfer of the coordinated S-5(2-) chain in 3 to selected organic compounds, such as MeI, PhCH2Br and PhCOCl, for the generation of organopolysulfido compounds has been demonstrated.

Automated summary

A new mononuclear cobalt(III)-pentasulfido compound has been synthesized through a convergent redox reaction between two new cobalt(II)-thiolato compounds and elemental sulfur. This compound, which has a low-spin, diamagnetic Co(III) center with a coordinated pentasulfido chain, is unprecedented in the literature.