Ligand-Based H2 Transfer with Dihydrazonopyrrole Complexes of Nickel

Biology uses precise control over proton, electron, H-atom, or H2 transfer to mediate challenging reactivity. While synthetic complexes have made incredible strides in replicating secondary coordination electron or proton donors, there are comparatively fewer examples of ligands that can mediate both proton and electron storage. Rarer still are ligands that can store full H2 equivalents. Here we report a dihydrazonopyrrole Ni complex where an H2 equivalent can be stored on the ligand periphery without any redox change at the metal center. This ligand-based storage of H2 can be leveraged for catalytic hydrogenations. Kinetic and computational analysis suggests a rate determining H2 binding step followed by comparatively facile H–H scission to hydrogenate the ligand. This system is an unusual example where a synthetic system can mimic biology’s ability to mediate H2 transfer via secondary coordination sphere-based processes.