Redox-Switchable Hydroelementation of a Cobalt Complex Supported by a Ferrocene-Based Ligand

The first crystallographically
characterized tetrahedral cobalt
salen (salen = N,N′-ethylenesalicylimine)
complex was synthesized by using a 1,1′-ferrocene derivative,
salfen (salfen = 1,1′- di­(2,4-di-tert-butyl-6-salicylimine)­ferrocene).
The complex undergoes two oxidation events at low potentials, which
were assigned as ligand centered by comparison to the corresponding
zinc complex. The cobalt complex was found to catalyze the hydroalkoxylation
of styrenes, similarly to related square planar cobalt salen complexes,
likely due to its fluxional behavior in alcoholic solvents. Furthermore,
the one-electron-oxidized species was found to be inactive toward
hydroalkoxylation. Thus, the hydroalkoxylation reactivity could be
turned on/off in situ by redox chemistry.