The synthesis of weak chemical bonds at or near thermodynamic potential is a fundamental challenge in chemistry, with applications ranging from catalysis to biology to energy science. Proton-coupled electron transfer using molecular hydrogen is an attractive strategy for synthesizing weak element–hydrogen bonds, but the intrinsic thermodynamics presents a challenge for reactivity. Here we describe the direct photocatalytic synthesis of extremely weak element–hydrogen bonds of metal amido and metal imido complexes, as well as organic compounds with bond dissociation free energies as low as 31 kcal mol⁻¹. Key to this approach is the bifunctional behaviour of the chromophoric iridium hydride photocatalyst. Activation of molecular hydrogen occurs in the ground state and the resulting iridium hydride harvests visible light to enable spontaneous formation of weak chemical bonds near thermodynamic potential with no by-products. Photophysical and mechanistic studies corroborate radical-based reaction pathways and highlight the uniqueness of this photodriven approach in promoting new catalytic chemistry.

合成处于或接近热力学势的弱化学键是化学中的一项基本挑战，其应用范围从催化到生物学再到能源科学。使用分子氢的质子耦合电子转移是合成弱元素-氢键的一种有吸引力的策略，但本征热力学对反应性提出了挑战。在这里，我们描述了金属氨基和金属亚氨基配合物的极弱元素-氢键的直接光催化合成，以及键离解自由能低至 31 kcal mol ^{-1的有机化合物}. 这种方法的关键是发色氢化铱光催化剂的双功能行为。分子氢的活化发生在基态，由此产生的氢化铱会收集可见光，从而能够在接近热力学势的情况下自发形成弱化学键，而不会产生副产物。光物理和机理研究证实了基于自由基的反应途径，并强调了这种光驱动方法在促进新催化化学方面的独特性。