Ab initio molecular dynamics study of water oxidation reaction pathways in mono-Ru catalysts.

Ab initio molecular dynamics simulations with an adaptive biasing potential are carried out to study the reaction path in mononuclear Ru catalysts for water oxidation of the type (Ar)Ru(X)(bpy) with different aromatic ligands (Ar). The critical step of the O-O bond formation in the catalytic cycle starting from the (Ar)Ru(O)(bpy) intermediate is analyzed in detail. It is shown that an explicit inclusion of the solvent environment is essential for a realistic description of the reaction path. Clear evidence is presented for a concerted reaction in which the O-O bond formation is quickly followed by a proton transfer leading to a Ru-OOH intermediate and a hydronium ion. An alternative path in which the approaching water first coordinates to the metal centre is also investigated, and it is found to induce a structural instability of the catalyst with the breaking of the aromatic ligand coordination bond.