NEW WATER OXIDATION CATALYSTS BASED ON CYANIDEBRIDGED RUTHENIUM POLYPYRIDINES

ABATE, PEDRO O.; JUÁREZ, MARÍA V.; BARALDO, LUIS M.

Montevideo

Conferencia; Humboldt Kolleg: Expanding the Frontiers of Science: A Transdisciplinary Approach; 2022

Alexander von Humboldt Foundation

in order to reduce the use of fossil fuels as a source of energy, one of the strategies explored for fuel generation is to simulate the photosynthetic process that occurs in the plant kingdom, which consists of two semi-reactions: water oxidation and CO2 reduction. The first reaction is considered the bottleneck since it is kinetically demanding as it involves the coupled transfer of 4 protons and 4 electrons. With this in mind, the development of water oxidation catalysts (WOC´s) is imperative [1]. Among the most efficient WOC´s based on Ru complexes are those containing the bda ligand (with bda = 6,6´-dicarboxy-2,2´-bipyridine) [2]. In this work we propose to explore the influence on the catalytic properties by coupling a redox center to two [Ru(bda)(DMSO)] units.In the present work we report the synthesis and characterization of three new polypyridine Ru complexes of formula: [(DMSO)Ru(bda)(py)4(μ-NC)Ru(py)4(μ-CN)Ru(bda)(DMSO)] (1), trans-[Ru(CN)2(tbutpy)4] (2) and [(DMSO)Ru(tbutpy)4(μ-NC)Ru(tbutpy)4(μ-CN)Ru(bda)(DMSO)] (3) (with tbutpy = 4-tert-butylpyridine, py = pyridine). The synthesized complexes were characterized by spectroscopic, electrochemical and computational techniques. One- and two-dimensional NMR spectroscopy measurements allowed the establishment of the symmetric structure of the synthesized complexes and the assignment of the 1H and 13C shifts. From the results of TD-DFT calculations they assigned the transitions observed in the UV-Vis spectra for the synthesized complexes. From electrochemical and oxidation kinetic measurements with [NH₄]₂[Ce(NO₃)₆], as shown in Fig. 1, it was determined that the mechanism for water oxidation catalyzed by (1) corresponds to one of unimolecular type (WNA) with a rate constant kWNA = 0.130 s-1.