Nitrogenase‐Inspired Mo‐Ru‐Mo Electron Bridge Anchored in Covalent Organic Frameworks for Efficient Photocatalytic Nitrogen Reduction

Abstract The photocatalytic nitrogen (N ₂ ) reduction reaction (NRR) is a promising route for sustainable ammonia (NH ₃ ) synthesis, yet it is limited by the inefficient and non‐directional transfer of electrons from light‐harvesters to catalytic sites. Inspired by the directional electron‐relay function in nitrogenases, this is rationally designed and synthesized a V‐shaped, trimetallic molybdenum‐ruthenium‐molybdenum (Mo‐Ru‐Mo, RuMo ₂ ) electron bridge, anchored within the bipyridine‐based covalent organic frameworks (COFs) for efficient NRR. This biomimetic electron bridge, featuring a central Ru(II) photosensitizer flanked by two Mo(VI) catalytic centers via bipyrimidine linkers, with two ultra‐short (≈5.4 Å) Ru‐to‐Mo electron transfer channels. Remarkably, the optimized catalyst, COF‐2‐RuMo ₂ , achieved an impressive ammonia production rate of 406.6 µmol g ⁻¹ h ⁻¹ , an 8‐fold enhancement over the pure COF‐2. Comprehensive photophysical studies and density functional theory (DFT) calculations reveal that the RuMo ₂ bridge promotes efficient exciton dissociation, facilitates rapid dual‐channel electron transfer to the Mo centers, and enables effective N ₂ activation via a synergistic electronic effect, following an alternating reduction pathway. This work offers valuable insights into the structural design of COF‐based photocatalysts featuring engineered electron transfer pathways.