Oxygen Activation by Co(II) and a Redox Non-Innocent Ligand: Spectroscopic Characterization of a Radical–Co(II)–Superoxide Complex with Divergent Catalytic Reactivity

Bimetallic (Et4N)2[Co2(L)2], (Et4N)2[1] (where (L)3– = (N­(o-PhNC­(O)iPr)2)3–) reacts with 2 equiv of
O2 to form the monometallic species (Et4N)­[Co­(L)­O2], (Et4N)­[3]. A crystallographically
characterized analog (Et4N)2[Co­(L)­CN], (Et4N)2[2], gives insight into the structure
of [3]1–. Magnetic measurements indicate
[2]2– to be an unusual high-spin CoII-cyano species (S = 3/2), while IR, EXAFS,
and EPR spectroscopies indicate [3]1– to be an end-on superoxide complex with an S =
1/2 ground state. By X-ray spectroscopy and calculations, [3]1– features a high-spin CoII center;
the net S = 1/2 spin state arises after the Co electrons
couple to both the O2•– and the
aminyl radical on redox non-innocent (L•)2–. Dianion [1]2– shows both nucleophilic
and electrophilic catalytic reactivity upon activation of O2 due to the presence of both a high-energy, filled O2– π* orbital and an empty low-lying O2– π* orbital in [3]1–.