Catalytic water oxidation induced by phenolato-bridged diMn complexes adsorbed on kaolin clay

SIGNORELLA, S.; BELLÚ, S.; PÉREZ, J.; FERRÓN, J.

Granada

Conferencia; 11th European Biological Inorganic Chemistry conference; 2012

Universidad de Granada

Water oxidation to evolve O2 is a fundamental chemical reaction in photosynthesis. The reaction is catalyzed by a unique Mn enzyme whose active site is comprised of an oxo-bridged tetramanganese cluster. Developing a stable and efficient catalytic system for water oxidation is the most challenging part of the water splitting reaction [1]. We found that adsorption of [Mn2L(OMe)(MeOH)2]ClO4, where L = 2,6-bis[((benzyl)(2-hydroxy-5-X-benzyl)amino)metil]-4-methylphenol (X = H, Cl, Me), 2,6-bis[((2-hydroxy-5-nitrophenyl)(2-hydroxy-benzyl)amino)metil]-4-methylphenol  or 2,6-bis[((2-pyridylmethyl)(2-hydroxy-5-Y-benzyl)amino)metil]-4-methylphenol (Y = Cl, Me), onto kaolin yielded successful functional mimics of the oxygen evolving center. Reaction of 1 (X = H)/kaolin with CeIV or ClO- in water produced a significant amount of O2 in contrast to results obtained in homogeneous phase (as shown in the figure for the 1/kaolin (0.05 mmol/mg) + 90 mM CeIV system). Kinetic studies revealed that catalytic activity increased with catalyst adsorbed on clay and was higher as the amount of clay was lower (at constant catalyst amount). X-ray photoelectron spectroscopy and electron paramagnetic resonance were used to characterize electronic changes of the catalysts adsorbed on kaolin during reaction. Comparison of kinetic parameters, redox potentials and electronic structure changes of compounds of this series provides insights into the water oxidation catalysis, including important factors influencing catalytic activity.