Surface-assisted transfer hydrogenation catalysis on a γ-Al2O3-supported Ir dimer

Area of Science:

• Heterogeneous catalysis
• Organometallic chemistry
• Surface science

Background:

• Iridium complexes are effective catalysts for hydrogenation reactions.
• Developing supported catalysts with enhanced activity and stability is crucial for industrial applications.
• Understanding the interaction between metal complexes and oxide supports is key to designing efficient catalysts.

Purpose of the Study:

• To synthesize and characterize a novel oxide-supported iridium dimer catalyst.
• To investigate the catalytic activity of the supported iridium dimer for transfer hydrogenation of aromatic ketones.
• To elucidate the structural features and surface interactions responsible for the enhanced catalytic performance.

Main Methods:

• Synthesis of an iridium dimer complex [Ir(2){η(5)-C(5)(CH(3))(5)}(2)(μ-CH(2))(2)] (Ir(2)).
• Preparation of γ-Al(2)O(3)-supported Ir(2) (Ir(2)/γ-Al(2)O(3)) catalyst.
• Detailed characterization of the supported catalyst using advanced techniques.
• Evaluation of catalytic activity in transfer hydrogenation of aromatic ketones.

Main Results:

• The Ir(2)/γ-Al(2)O(3) catalyst exhibited high activity for transfer hydrogenation, with a turnover number of 699 (24 h) for acetophenone.
• Characterization revealed bridged Ir-(OAl)(2)-Ir bonds at the interface between the Ir dimer and the γ-Al(2)O(3) surface.
• The supported catalyst significantly outperformed homogeneous Ir(2) and Ir(2) supported on SiO(2) and MgO.
• A structural transformation leading to an Ir(2)-H(2)/γ-Al(2)O(3) intermediate was proposed to facilitate catalysis.

Conclusions:

• The γ-Al(2)O(3) support plays a critical role in stabilizing the Ir dimer and enhancing its catalytic activity.
• Bridged Ir-(OAl)(2)-Ir bonds are essential for the high performance of the supported catalyst.
• The study provides insights into the dynamic behavior of oxide surfaces in hydrogen transfer catalysis.