Square-planar structures radical formation

The sterically crowded ligand (106) forms a very rare square-planar Co complex, as shown by an X-ray crystal structure, and a spin triplet (paramagnetic) ground state was also identified in the solid state. The Co complex of (107) catalyzes the epoxidation of norbomene with t-BuOOH or Phi as terminal oxidant, catalysis driven by formation of t-BuOO radicals employing a Co redox process. 

In the past, ESR studies on isoxazole(s) revealed the formation and structure of radical as well as the stereochemical information of metallic complexes. It has been reported that the metal appears to be 4-coordinate square planar in bis complexes and hexacoordinate in tetrakis complexes... 

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