Vitamin B₁₂ is a unique metal complex which has the cobalt ion and the corrin as a centered metal and a ligand, respectively. The Co(I) state of the vitamin B₁₂ reacts alkyl halide to form alkylated complex by the S_N2 type reaction and proceed the several catalytic reactions via alkyl radicals formed by homolysis of the cobalt-carbon bond.^[1] Based on these properties of the vitamin B₁₂, many B₁₂-inspired reactions have been developed.^[2] In general, many researchers have used the cobyrinate complex (1) as the B₁₂ derivatives. Here, we report the synthesis and characterization of the Co(II) state of pyrocobseter (2) with π-expanded structure and the reactivities of the complex will be discussed.

The pyrocobester was synthesized by the pyrolysis of the cobyrinate.^[3] The absorption of the pyrocobester showed efficiently red-shift compared to the cobyrinate because of the conjugated corrin ligand. Furthermore, Co(II)/Co(I) redox potentials were +0.3 V shifted (Figure 1). In addition, the spectrum was dramatically changed after adding the CH₃I as the substrate. It is suggested that Co(I) state of pyrocobester reacted with CH₃I and alkylated complex (CH₃-Co(III)) was formed. In this presentation, we will report experimental detail of pyrocobester chemistry.

References

[1] D. Gryko et al., Chem. Soc. Rev., 2015, 44, 3391.

[2] H. Shimakoshi, Y. Hisaeda, Chem. Rec., 2021, 21, 2080.

[3] B. Kraütler et al., Helv. Chim. Acta., 1983, 66, 1493.