Cooperative water oxidation catalysis in a series of trinuclear metallosupramolecular ruthenium macrocycles. Issue 10 (4th September 2017)

• Record Type: Journal Article
• Authors: Kunz, Valentin; Lindner, Joachim O.; Schulze, Marcus; Röhr, Merle I. S.; Schmidt, David; Mitrić, Roland; Würthner, Frank
• Is Part Of: Energy & environmental science. Volume 10:Issue 10(2017)
• Page Start: 2137
• Page End: 2153
• Publication Date: 2017-09-04
• Subjects: Energy conversion -- Periodicals; Fuel switching -- Periodicals; Environmental sciences -- Periodicals; Environmental chemistry -- Periodicals; 333.79
• DOI: 10.1039/c7ee01557g
• Languages: English
• ISSNs: 1754-5692

Abstract

Abstract : Well-defined hydrogen-bonded water networks inside differently sized ruthenium macrocycles facilitate cooperative proton-coupled electron transfers, and accelerate the water oxidation catalysis. Abstract : A series of trinuclear metallosupramolecular Ru(bda) macrocycles has been synthesized and the impact of the ring size on the catalytic activity in homogeneous water oxidation has been elucidated (bda = 2, 2′-bipyridine-6, 6′-dicarboxylate). Kinetic experiments revealed that for all macrocyclic catalysts a proton-coupled oxidation event is rate-determining. Distinct H/D kinetic isotope effects (KIE) have been observed for the individual macrocycles, which follow the same tendency like the catalytic activity where an intermediate ring size exhibits the best performance. To get insight into the different molecular properties, molecular dynamics simulations using a QM/MM approach have been performed for all reaction steps, revealing that the size of the cavity strongly influences the hydrogen-bonded water network inside the macrocyclic structure and thus, important proton-coupled reaction steps of the catalytic cycle. For the most active catalysts, all reactive sites point into the interior of the cavity, which is supported by a single crystal X-ray analysis of the largest macrocycle, and a cooperative effect between the individual Ru(bda) centers facilitating proton abstraction has been substantiated. On the other hand, different structural conformations predominate the smaller macrocycles, which prevent efficient interactions between the Ru(bda) centers.