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Hemilability Modulation via Phosphane-Triazole Ligand Design: Impact on Catalytic Formic Acid Dehydrogenation

Year: 2025

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide Two novel P–N ligands, 1-[2-(diphenylphosphanyl)ethyl]-1 H -benzo-1,2,3-triazole ( 1 ) and its N2-isomer ( 2 ), were synthesized. Reaction of 1 and 2 with [Ir(μ-Cl)(cod)] 2 and [Rh(μ-Cl)(cod)] 2 in a 2:1 molar ratio followed by AgBF 4 led to the formation of square-planar κ 2 - P, N complexes, Ir-1, Ir-2, Rh-1 and Rh-2 . Density functional theory studies provided insights into the electronic structure and bonding of the complexes. Complex Ir-3 was also prepared for comparison, employing ligand 3, 1-[2-(diphenylphosphanyl)methyl]-1 H -benzo-1,2,3-triazole. Variable-temperature NMR studies on [IrCl(cod)(P–N)] complexes revealed fluxional behavior attributed to ligand hemilability. Activation Gibbs free energies (Δ G ‡ ) for the isomerization equilibrium of [IrCl(cod)(PN)] complexes featuring ligands 1, 2 and 3 are 10.24, 10.60, and 8.87 kcal·mol –1, respectively. This enabled us to propose a coordination-ability scale that follows the trend 3 > 1 > 2 . The relative activities of the iridium complexes were evaluated in the dehydrogenation of formic acid. Under optimized conditions, in an HCOOH/Et 3 N mixture, the initial TOFs are 186, 828, and 948 h –1 for Ir-1, Ir-2, and Ir-3, respectively. This indicates that Ir-3, bearing the most strongly coordinating ligand, exhibits the highest catalytic activity, reaching a TON value of 444 after 7 h. This study demonstrates the tunability of the hemilability of benzo-1,2,3-triazole-based P–N ligands and their potential for modulating catalytic activity.

Source: Inorganic Chemistry

DOI: 10.1021/acs.inorgchem.5c03962