Redox-switchable catalysis utilizes redox active ligands to influence the catalytic activities displayed by coordinated metals. Christopher W. Bielawski and his group, University of Texas at Austin, USA, in collaboration with Stephen Sproules, University of Glasgow, UK, have designed ferrocene-containing N-heterocyclic carbenes, by means of a straightforward synthesis, and ligated these compounds to a series of iridium and catalytically active ruthenium complexes.

The team found that the catalytic activity displayed by a Hoveyda–Grubbs ruthenium complex outfitted with a ferrocene containing ligand in the ring-closing metathesis reaction of diethyl diallylmalonate could be controlled by changing the oxidation state of the redox-active moiety. Indeed, the complex could be switched between states of relatively low and high catalytic activity by adding stoichiometric quantities of a mild oxidant or reducing agent, respectively.

Since catalytic activity is often intimately tied to the electronic properties of ligated metals, these results may pave new avenues for modulating the intrinsic chemo- and regioselectivities displayed by catalysts supported by redox-switchable N-heterocyclic carbenes.

• Redox-Switchable Ring-Closing Metathesis: Catalyst Design, Synthesis, and Study,
  K. Arumugam, C. D. Varnado, Jr., S. Sproules, V. M. Lynch, C. W. Bielawski,
  Chem. Eur. J. 2013.
  DOI: 10.1002/chem.201301247