Bimetallic reactivity. One-site addition two-metal oxidation reactions using a di-Co(II) complex of a binucleating ligand with 5-and 6-coordinate sites

The preparation of an unsymmetrical binucleating ligand bearing a bridging oxadiazole ring flanked on one side by three ligands and on the other by fo ur ligands is described. When bound to two metals, the ligand forms complex es where the metals are in 5- and 6-coordinate sites after the incorporatio n of an exogenous bridging ligand. A di-Co2+ complex of th is ligand has be en prepared containing a hydroxide bridge. The complex is readily oxidized to the di-Co3+ state by outer sphere electron transfer with ferrocenium ion s. Addition of Br-2 or NO2+ to the di-Co2+ complex leads to the rapid forma tion of the di-Co3+ bromo or nitro complexes, respectively. The ligand char acteristics which allow for double oxidation with ferrocenium ions and for the one-site addition two-metal oxidations with Br-2 and NO2+ are discussed in terms of mechanical coupling between the two metal sites.