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

Area of Science:

• Organometallic Chemistry
• Catalysis
• Ligand Design

Background:

• Development of novel P-N ligands is crucial for advancing homogeneous catalysis.
• Benzo-1,2,3-triazole-based ligands offer tunable electronic and steric properties.
• Understanding ligand hemilability is key to optimizing catalyst performance.

Purpose of the Study:

• Synthesize and characterize novel P-N ligands and their corresponding iridium and rhodium complexes.
• Investigate the electronic structure, bonding, and fluxional behavior of these metal complexes.
• Evaluate the catalytic activity of the iridium complexes in formic acid dehydrogenation.

Main Methods:

• Synthesis of two novel P-N ligands and their N2-isomer.
• Formation of square-planar P,N-chelating iridium(I) and rhodium(I) complexes.
• Characterization using Density Functional Theory (DFT) studies and Variable-Temperature Nuclear Magnetic Resonance (VT-NMR) spectroscopy.
• Catalytic evaluation in formic acid dehydrogenation.

Main Results:

• Successful synthesis of P-N ligands 1, 2, and 3, and their corresponding iridium and rhodium complexes (Ir-1, Ir-2, Rh-1, Rh-2).
• DFT studies provided insights into electronic structure and bonding.
• VT-NMR revealed fluxional behavior attributed to ligand hemilability, enabling a coordination-ability scale: 3 > 1 > 2.
• Iridium complexes exhibited varying catalytic activities in formic acid dehydrogenation, with Ir-3 showing the highest activity (TOF: 948 h⁻¹, TON: 444).

Conclusions:

• The hemilability of benzo-1,2,3-triazole-based P-N ligands can be effectively tuned.
• Ligand coordination ability directly correlates with catalytic activity in formic acid dehydrogenation.
• The synthesized P-N ligands and their metal complexes show significant potential for catalytic applications.