Low-spin cobalt(ii) redox shuttle by isocyanide coordination

Coordination of the strong-field ligand 2,6-dimethylphenyl isocyanide (DMP-CN) to the Co(PY5Me(2)) framework, where PY5Me(2) represents the pentadentate ligand 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine, has resulted in a new low-spin Co(ii) complex with a relatively low reorganization energy and fast electron-transfer kinetics compared to the prototypical cobalt tris-bipyridine redox shuttle, [Co(bpy)(3)](3+/2+), where bpy represents 2,2 '-bipyridine. Despite nearly 160 mV reduced regeneration driving force, the [Co(PY5Me(2))(DMP-CN)](3+/2+) redox shuttle displayed an increased regeneration efficiency relative to [Co(bpy)(3)](3+/2+), however recombination losses hinder the performance as evidenced by a reduced recombination resistance. Future directions point to low-spin Co(ii) redox shuttles with more negative redox potentials to be paired with a dye or dye mixture that absorbs into the near infrared region.