Deciphering the mechanistic landscape of formic acid dehydrogenation with the heterobimetallic Ir(III)-Ni(II) catalyst.

Heterobimetallic catalysts have garnered significant attention due to their potential to achieve synergistic effects in catalytic transformations. However, the mechanistic complexity arising from the interactions between distinct metal centers and multifunctional ligands poses substantial challenges for rational catalyst design. This study systematically investigates the reaction mechanism of Ir(III)-Ni(II) heterobimetallic complexes in the catalytic dehydrogenation of formic acid through density functional theory (DFT) calculations. A detailed comparison between the reaction pathways using formic acid (HCOOH) and formate (HCOO) as substrates was conducted. When formate serves as the reactant, the Ir(III) center follows the classical β-hydrogen elimination mechanism, consistent with established single-metal dehydrogenation paradigms. In contrast, when formic acid is employed as the substrate, a novel, previously unreported ligand-assisted outer-sphere hydrogen transfer mechanism is revealed: while the Ni(II) center does not directly coordinate to the substrate, it facilitates proton transfer the 2,6-pyridinedicarboxylate ligand, demonstrating its indirect yet critical role. Kinetic and thermodynamic analyses indicate that H gas release constitutes the rate-determining step for both pathways, aligning with experimental observations. These findings elucidate an innovative strategy for achieving metal-ligand cooperation catalysis in heterobimetallic systems and provide a robust theoretical foundation for the development of next-generation bifunctional catalysts capable of efficiently dehydrogenating formic acid under mild conditions.