Establishing the Family of Diruthenium Water Oxidation Catalysts Based on the Bis(bipyridyl)pyrazolate Ligand System

Abstract

A bis(bipyridyl)pyrazolate ((Me)bbp(-)) has recently been introduced as a rugged dinucleating, bis(tridentate) ligand for the formation of efficient diruthenium water oxidation catalysts (J. Am. Chem. Soc. 2014, 136, 24-27). Now, detailed protocols for the synthesis of a whole family of such dinuclear ruthenium complexes [{Ru(pyR(2))2}2(μ-(R1)bbp)(X,Y)](2+) based on the bis(bipyridyl)pyrazolate scaffold are reported. The isolation of a synthetic key intermediate allowed the straightforward introduction of different pyridines as axial ligands. Thereby, a set of complexes with different substituents at the pyrazolate backbone (R(1) = Br, H, Me), different pyridines as axial ligand (R(2) = H, NMe2, SO3), and different (non)bridging units in the in,in-position (X,Y = Cl, H2O, OAc) has been prepared and thoroughly characterized. Complexes of the type [{Ru(pyR(2))2}2(μ-(R1)bbp)(μ-OAc)](2+), with an exogenous acetato bridge, have been used as catalyst precursors in catalytic water oxidation experiments with a sacrificial oxidant. The effect of substitution on the pyrazole core of the (R1)bbp(-) ligand as well as on the pyridine ligands on both electrochemistry and catalytic activity has been systematically investigated. The catalyst stability, reflected by the turnover number, is crucially determined by the substituent at the pyrazolate ligand (R(1) = Me > H > Br). In contrast, the axial pyridine ligands modulate the rate of the catalytic process, expressed by the initial turnover frequency (R(2) = H > NMe2H(+)).

Foot of the Wave Analysis for Mechanistic Elucidation and Benchmarking Applications in Molecular Water Oxidation Catalysis

“…In both cases, we are assuming that the O−O bond formation is the RDS. Other scenarios for WOCs with different RDS steps are not considered in the present work; however, systems where the RDS is first order with regard to [Ru] will also be comprised within the equations of the WNA mechanisms, as the intramolecular O−O bond formation will be in dinuclear complexes . A complete mathematical description of the FOWA equations is presented in the Supporting Information and the most relevant equations are shown in Table .…”

“…Other scenarios for WOCs with different RDS steps are not considered in the present work;h owever,s ystems where the RDS is first order with regard to [Ru] will also be comprised within the equations of the WNAm echanisms, [49] as the intramolecular OÀOb ondf ormationw ill be in dinuclearc omplexes. [47,53,54] Ac omplete mathematical description of the FOWAe quations is presented in the Supporting Information and the most relevant equations are shown in Ta ble 1. It is worth mentioning that for the WNA mechanism, k WNA is an apparent pseudo-rate constantd efined as k WNA = k 1 [H 2 O] (see Ta ble 1) that is associatedw ith the chemical reaction following ET [Eq.…”

Catalytic Oxidation of Water to Dioxygen by Mononuclear Ru Complexes Bearing a 2,6‐Pyridinedicarboxylato Ligand

“…Single crystals of both the Ru II and Ru III species were obtained and their structures are shown in Figure B and C, respectively. Complex 2 II displays the typical slightly distorted octahedral geometry around the ruthenium, as expected for a low‐spin d 6 Ru II ion . The bpy ligands occupy both the axial and equatorial positions assuming the κ‐N 1 O 1 ‐pdc 2− ligands bound in the equatorial plane, with a dangling carboxylate not bonded to Ru.…”

Ditopic Hexadentate Ligands with a Central Dihydrobenzo‐diimidazole Unit Forming a [2x2] Zn4 Grid Complex

“…[6,7] The resulting complexes feature different catalytic, magnetic, and photophysical properties and may enable new cooperative functionality. [8][9][10][11][12] In this context, a number of bimetallic complex catalysts have been reported, e. g., in asymmetric allylic alkylation, [13] water oxidation, [14][15][16][17][18] epoxidation, [19] and transfer hydrogenation of ketones. [20] The probably most adaptable and established ligands for this purpose are derivatives of 2,2':6',2"-terpyridine (terpy) type containing, inter alia, pyrazole, tetrazole, and imidazole subunits.…”