Making Oxygen with Ruthenium Complexes

TLDR: A general reactivity toward water oxidation in a class of molecules whose properties can be "tuned" systematically by synthetic variations based on mechanistic insight is described.

Abstract: Mastering the production of solar fuels by artificial photosynthesis would be a considerable feat, either by water splitting into hydrogen and oxygen or reduction of CO2 to methanol or hydrocarbons: 2H2O + 4hν → O2 + 2H2; 2H2O + CO2 + 8hν → 2O2 + CH4. It is notable that water oxidation to dioxygen is a key half-reaction in both. In principle, these solar fuel reactions can be coupled to light absorption in molecular assemblies, nanostructured arrays, or photoelectrochemical cells (PECs) by a modular approach. The modular approach uses light absorption, electron transfer in excited states, directed long range electron transfer and proton transfer, both driven by free energy gradients, combined with proton coupled electron transfer (PCET) and single electron activation of multielectron catalysis. Until recently, a lack of molecular catalysts, especially for water oxidation, has limited progress in this area. Analysis of water oxidation mechanism for the “blue” Ru dimer cis,cis-[(bpy)2(H2O)RuIIIORuIII(OH2)(b...