Pushing Single-Oxygen-Atom-Bridged Bimetallic Systems to the Right: A Cryptand-Encapsulated Co–O–Co Unit

A dicobalt(II) complex, [Co2­(mBDCA-5t)]2– (1), demonstrates a cofacial
arrangement of trigonal mono­pyramidal Co(II) ions with an inter-metal
separation of 6.2710(6) Å. Reaction of 1 with potassium
superoxide generates an encapsulated Co–O–Co core in
the dianionic complex, [Co2O­(mBDCA-5t)]2– (2); to form the linear Co–O–Co
core, the inter-metal distance has diminished to 3.994(3) Å.
Co K-edge X-ray absorption spectroscopy data are consistent with a
+2 oxidation state assignment for Co in both 1 and 2. Multi­reference complete active space calculations
followed by second-order perturbation theory support this assignment,
with hole equivalents residing on the bridging O-atom and on the cryptand
ligand for the case of 2. Complex 2 acts
as a 2-e– oxidant toward substrates including CO
and H2, in both cases efficiently regenerating 1 in what represent net oxygen-atom-transfer reactions. This dicobalt
system also functions as a catalase upon treatment with H2O2.