Hydrogen Bond‐Assisted PCET and Formation of WIII─OH in Bis(Dithiolene) Complex

Abstract

<jats:title>Abstract</jats:title><jats:p>The redox non‐innocent nature of dithiolene ligands is well known for stabilizing high‐valent metal ions and facilitating proton‐coupled electron transfer (PCET) processes. Until now, proton reactivity at the dithiolene site has been primarily associated with low‐valent metal centers, as high‐valent metal‐dithiolene complexes were not considered viable for such reactivity. This study introduces high‐valent bis(dithiolene) tungsten (W)‐oxo complexes featuring hydrogen‐bonding interactions, unveiling a novel proton reduction mechanism mediated by the dithiolene moiety. The process begins with a nucleophilic W‐oxo, forming a hydrogen bond, followed by a second hydrogen bond at the dithiolene‐sulfur (S) site. These hydrogen‐bonding interactions significantly modulate the molecular orbital energy levels, enabling the W<jats:sup>IV→III</jats:sup> reduction at −1.75 V (<jats:italic>E</jats:italic><jats:sub>exp</jats:sub>) and allowing, for the first time, the acquisition of an EPR spectrum of a W<jats:sup>III</jats:sup>─OH intermediate species. In contrast, direct electron transfer into the W<jats:sup>IV</jats:sup>═O state would populate the dithiolene π* orbital, demanding substantially larger energy (<jats:italic>E</jats:italic><jats:sub>cal</jats:sub>= −3.45 V). For catalytic proton reduction, the proton transfer through the dithiolene‐S site was identified as the energetically most favorable pathway for generating the W<jats:sup>V</jats:sup>─H catalytic species.</jats:p>