Probing Ligand Effects on O–O Bond Formation of Ru-Catalyzed Water Oxidation: A Computational Survey

Runhua Kang †, Kejuan Chen †, Jiannian Yao *†,Sason Shaik ‡, and Hui Chen *†

† Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China

‡ Institute of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, Givat Ram Campus, 91904, Jerusalem, Israel

Inorg. Chem., Article ASAP

DOI: 10.1021/ic500008c

Publication Date (Web): June 26, 2014

*E-mail: chenh@iccas.ac.cn (H.C.)., *E-mail: jnyao@iccas.ac.cn (J.Y.).

Synopsis

For mononuclear Ru-based water oxidation catalysts (WOCs), our systematic DFT calculations have identified and rationalized that there are several factors affecting the O−O bond formation process: (1) a phenyl or carbene group cis to the proton-accepting moiety in the WNA mechanism; (2) the net charge of the system; and (3) steric hindrance for a very bulky ligand in the I2M mechanism. All of these factors can potentially be subjects of adjustment in future ligand design.

Section:

Physical Organic Chemistry

Abstract

Ligand effects of some representative monomeric Ru-based water oxidation catalysts on the key O–O formation step are revealed in this work. Three effects, namely, cis-effect, net charge effect, and steric hindrance effect, are identified, which can exert sizable modulation on the O–O formation barriers for the two widely accepted O–O formation mechanisms of WNA (water nucleophilic attack) and I2M (direct coupling of two high-valent metal oxo units). The study demonstrates that, through the way of ligand design, there remains a large space for improving O–O bond formation reactivity.

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