Reductive Photocatalytic Proton‐Coupled Electron Transfer by a Zirconium‐Based Molecular Platform

Reductive proton‐coupled electron transfer (PCET) has important energetic implications in numerous synthetic and natural redox processes. The development of catalytic systems that can mediate such transformations has become an attractive target, especially when light is used to generate the reactive species towards solar‐to‐chemicals conversion. However, such approach becomes challenged by kinetic competition with H2 evolution. Here we describe the excited state reactivity of a molecular Zr‐based platform under visible light irradiation for the efficient reduction of multiple bonds. Mechanistic investigations shine light on a charge separation process that colocalizes an excited electron and an acidic proton to promote selective PCET. We further leveraged this reactivity for the photocatalytic reduction of a variety of organic substrates. Our results demonstrate the promise of this molecular platform to design strong photocatalytic PCET mediators for reductive transformations. More broadly, we also show the potential relevance of PCET mechanisms in the (photo)redox chemistry of Zr‐based molecular materials. Insert text for Table of Contents here: Light irradiation of a Zr‐based coordination compound provides a potent, excited state proton‐coupled electron transfer (PCET) donor that remains stable against hydrogen evolution. Instead, this species can catalyze the reduction of multiple organic substrates (Sub), demonstrating its potential for solar‐to‐chemical applications and providing valuable insight into the photoredox chemistry of Zr−OH motifs.