de Gracia Triviño Juan Angel, Ahlquist Mårten S G
Division of Theoretical Chemistry and Biology, Department of Chemistry, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, 10691 Stockholm, Sweden.
PDC Center for High-Performance Computing, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, 10691 Stockholm, Sweden.
J Phys Chem A. 2024 May 16;128(19):3794-3800. doi: 10.1021/acs.jpca.4c00404. Epub 2024 May 6.
The Ru(tda) catalyst has been a major milestone in the development of molecular water oxidation catalysts due to its outstanding performance at neutral pH. The role of the noncoordinating carboxylate group is to act as a nucleophile, donating an oxygen atom to the oxo group, thereby acting as an oxide relay (OR) mechanism for O-O bond formation. A substitution of the carboxylates for phosphonate groups has been proposed, resulting in the Ru(tPaO) catalyst, which has shown even more efficient performance in experimental characterization. In this study, we explore the feasibility of the OR mechanism in the newly reported Ru(tPaO) molecular catalyst. We investigated the catalytic cycle using density functional theory and identified a variation of the OR mechanism that involves radical oxygen atoms in O-O bond formation. We have also determined that the subsequent hydroxide nucleophilic attack is the sole rate-limiting step in the catalytic cycle. All activation free energies are very low, with a free-energy barrier of 2.1 kcal/mol for O-O bond formation and 4.2 kcal/mol for OH nucleophilic attack.
由于Ru(tda)催化剂在中性pH条件下具有出色的性能，它已成为分子水氧化催化剂发展中的一个重要里程碑。非配位羧酸盐基团的作用是作为亲核试剂，将一个氧原子提供给氧代基团，从而作为O-O键形成的氧化物中继（OR）机制。有人提出用膦酸酯基团取代羧酸盐，由此得到了Ru(tPaO)催化剂，该催化剂在实验表征中表现出了更高的效率。在本研究中，我们探讨了新报道的Ru(tPaO)分子催化剂中OR机制的可行性。我们使用密度泛函理论研究了催化循环，并确定了OR机制的一种变体，该变体在O-O键形成过程中涉及自由基氧原子。我们还确定，随后的氢氧根亲核攻击是催化循环中唯一的速率限制步骤。所有活化自由能都非常低，O-O键形成的自由能垒为2.1 kcal/mol，OH亲核攻击的自由能垒为4.2 kcal/mol。
