Installing Quinol Proton/Electron Mediators onto Non-Heme Iron Complexes Enables Them to Electrocatalytically Reduce O to HO at High Rates and Low Overpotentials.

We prepare iron(II) and iron(III) complexes with polydentate ligands that contain quinols, which can act as electron proton transfer mediators. Although the iron(II) complex with -(2,5-dihydroxybenzyl)-,','-tris(2-pyridinylmethyl)-1,2-ethanediamine (Hqp1) is inactive as an electrocatalyst, iron complexes with ,'-bis(2,5-dihydroxybenzyl)-,'-bis(2-pyridinylmethyl)-1,2-ethanediamine (Hqp2) and -(2,5-dihydroxybenzyl)-,'-bis(2-pyridinylmethyl)-1,2-ethanediamine (Hqp3) were found to be much more active and more selective for water production than a previously reported cobalt-Hqp1 electrocatalyst while operating at low overpotentials. The catalysts with Hqp3 can enter the catalytic cycle as either Fe(II) or Fe(III) species; entering the cycle through Fe(III) lowers the effective overpotential.