Organometallic Synthesis of Bimetallic Cobalt-Rhodium Nanoparticles in Supported Ionic Liquid Phases (Co x Rh 100- x @SILP) as Catalysts for the Selective Hydrogenation of Multifunctional Aromatic Substrates.

The synthesis, characterization, and catalytic properties of bimetallic cobalt-rhodium nanoparticles of defined Co:Rh ratios immobilized in an imidazolium-based supported ionic liquid phase (Co _x Rh _{100- x} @SILP) are described. Following an organometallic approach, precise control of the Co:Rh ratios is accomplished. Electron microscopy and X-ray absorption spectroscopy confirm the formation of small, well-dispersed, and homogeneously alloyed zero-valent bimetallic nanoparticles in all investigated materials. Benzylideneacetone and various bicyclic heteroaromatics are used as chemical probes to investigate the hydrogenation performances of the Co _x Rh _{100- x} @SILP materials. The Co:Rh ratio of the nanoparticles is found to have a critical influence on observed activity and selectivity, with clear synergistic effects arising from the combination of the noble metal and its 3d congener. In particular, the ability of Co _x Rh _{100- x} @SILP catalysts to hydrogenate 6-membered aromatic rings is found to experience a remarkable sharp switch in a narrow composition range between Co ₂₅ Rh ₇₅ (full ring hydrogenation) and Co ₃₀ Rh ₇₀ (no ring hydrogenation).
(© 2020 The Authors. Small published by Wiley-VCH GmbH.)