A bird's-eye view of the water splitting and H2 generation at a ruthenium(II) pincer complex is presented. Using a combination of density functional theory and efficient algorithms for exploration of potential energy hypersurface (PES), a total of 197 local minima and 186 transition states are identified, and a new mechanism for water splitting and H2 evolution via hydroxycarbonyl intermediates is presented. Furthermore, a global feature of the reaction PES, so-called potential energy landscape, is discussed on analyzing the obtained structures. As a result, the landscape is characterized by hierarchical structure, namely, PES consists of many "superbasins (SBs)" that are separated by relatively high energy barriers corresponding to bond breaking around Ru(II) center. Each SB involves a set of conformational isomers that can be interchanged with each other through relatively small barriers. To the best of our best knowledge, this is the first report on the quantum chemical computation of the hierarchical structure of PES for a realistic, catalytic reaction system.
Keywords: density functional theory; disconnectivity graph; energy landscape; energy surface; ruthenium pincer complex.
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