Fine-tuning dirhodium compounds with bridging ligands: Synthesis, structure, catalytic efficiency

Abstract

The structure of dirhodium compounds contains a unique Rh-Rh bond, two axial ligands and four bridging ligands. In the dirhodium(II) compounds, it is easy to migrate the coordinating atoms of the bridging ligand during the catalysis process, which leads to the degradation of the catalyst. Coordination atom migration was identified in bridging ligands. To improve the catalyst stability, we carried out a study on the effect of fine-tuning of the bridging ligand on the dirhodium compound. Several dirhodium compounds were designed and synthesized. During this process, we have successfully found Rh2(5-Br-esp)2 and Rh2(5-tBu-esp)2, which are closer to the ideal geometric configuration of the dirhodium(II) compounds. Rh2(5-Br-esp)2 has been applied in the oxidation of propargyl position and Rh2(5-tBu-esp)2 in the formation reaction of the C–N bond.