Oxo-bridged Tri- and Tetra-nuclear Cobalt Complexes Supported with Amide-Based Nitrogen Donor Ligands

This work presents two mixed-valent mu(3)-oxo-bridged trinuclear [(Co2+)(2)Co3+] complexes 1 and 2 and a mu(4)-oxo-bridged tetranuclear [Co-4(2+)] complex 3. Crystal structures of 1 and 2 showed the presence of triangular complexes having two Co2+ and one Co3+ centers bridged by a mu(3)-oxo group. In contrast, complex 3 exhibited a tetrahedrally arranged mu(4)-oxo-bridged [Co-4(2+)] core. A significant feature is the stabilization of unusual mu-oxo-bridged complexes exclusively supported with all nitrogen donor ligands. The X-ray photoelectron spectroscopy confirmed the multiple oxidation states of cobalt ions in these complexes. Such oxo-bridged cobalt complexes were investigated for their catalytic activity towards H2O2-mediated oxidation of assorted benzyl alcohols.