A naphthyridine‐derived expanded pincer ligand is described that can host two copper(I) centers. The proton‐responsive ligand can undergo reversible partial and full dearomatization of the naphthyridine core, which enables cooperative activation of H2 giving an unusual butterfly‐shaped Cu4H2 complex.

We report the synthesis and characterization of a series of cationic, neutral, and anionic dicopper­(I) complexes featuring a μ-mesityl ligand and a naphthyridine-derived PNNP expanded pincer ligand. Structural characterization showed that the protonation state of the dinucleating ligand has a pronounced effect on the bending and tilting of the μ-mesityl ligand. DFT calculations indicate that the varying orientations of the μ-mesityl ligand are inherent due to changes in electronic structure rather than crystal-packing effects. NBO analysis reveals how the interactions that contribute to the three-center–two-electron bond between the μ-mesityl ligand and the dicopper core change for the various degrees of observed bending and tilting.

α-Diimines are commonly used as supporting ligands for a variety of transition metal-catalyzed processes, most notably in α-olefin polymerization. They are also precursors to valuable synthetic targets, such as chiral...

<p>We report the synthesis and characterization of a series of cationic, neutral and anionic dicopper(I) complexes featuring a <i>µ</i>-mesityl ligand and a naphthyridine-derived PNNP expanded pincer ligand. Structural characterization showed that the protonation state of the dinucleating ligand has a pronounced effect on the bending and tilting of the <i>µ</i>-mesityl ligand. DFT calculations indicate that the varying orientations of the <i>µ</i>-mesityl ligand are inherent due to changes in electronic structure rather than crystal packing effects. NBO analysis reveals how the interactions that contribute to the 3-center 2-electron bond between the <i>µ</i>-mesityl ligand and the dicopper core change for the various degrees of observed bending and tilting. </p>

Understanding how multicopper oxidases (MCOs) reduce oxygen in the trinuclear copper cluster (TNC) is of great importance for development of catalysts for the oxygen reduction reaction (ORR). Herein, we report a mechanistic investigation into the ORR activity of the dinuclear copper complex [Cu 2 L(μ-OH)] 3+ (L = 2,7-bis[bis(2-pyridylmethyl)aminomethyl]-1,8-naphthyridine). This complex is inspired by the dinuclear T3 site found in the MCO active site and confines the Cu centers in a rigid scaffold. We show that the electrochemical reduction of [Cu 2 L(μ-OH)] 3+ follows a proton-coupled electron transfer pathway and requires a larger overpotential due to the presence of the Cu-OH-Cu motif. In addition, we provide evidence that metal−metal cooperativity takes place during catalysis that is facilitated by the constraints of the rigid ligand framework, by identification of key intermediates along the catalytic cycle of [Cu 2 L(μ-OH)] 3+ . Electrochemical studies show that the mechanisms of the ORR and hydrogen peroxide reduction reaction found for [Cu 2 L(μ-OH)] 3+ differ from the ones found for analogous mononuclear copper catalysts. In addition, the metal−metal cooperativity results in an improved selectivity for the four-electron ORR of more than 70% because reaction intermediates can be stabilized better between both copper centers. Overall, the mechanism of the [Cu 2 L(μ-OH)] 3+ -catalyzed ORR in this work contributes to the understanding of how the cooperative function of multiple metals in close proximity can affect ORR activity and selectivity.