Supramolecular Preorganization Rhodium and Iridium Metal Complexes Within M₁₂L₂₄ Self-Assembled Nanospheres for the Confined Synthesis Rh/Ir Alloyed Nanoparticles

Controlling the size and composition of metal nanoparticles is of considerable interest, as these are essential to their catalytic properties. Recently, our group has developed a preorganization strategy for controlled Ir nanoparticle synthesis inside Pt₁₂L₂₄ nanospheres. In the current contribution, we expand this method to the controlled synthesis of Rh nanoparticles. The encapsulated Rh^I complexes (Rh-s @ G-sphere) led to reasonable size control (2.8 ± 0.9 nm). Next, we demonstrated the formation of Rh-Ir alloyed nanoparticles with varying Rh/Ir compositions, by preorganization of the respective metal complexes inside Pt₁₂L₂₄ nanospheres based on complementary hydrogen bonds before the reduction step that leads to nanoparticle formation. These heterometallic particles were evaluated in the hydrogenation of cinnamaldehyde (7) as a probe reaction. Besides a high activity in this probe reaction, the Rh particles also catalyzed the conversion of the solvent (CH₃CN). The formed basic amine leads to follow-up reactions of the product and compatibility issues with the hosting nanosphere. The solvent hydrogenation was effectively suppressed by using the Rh:Ir alloyed nanoparticles, provided that they contain > 66% Ir. Compared to the monometallic Ir particles (Ir-s @ G-sphere), the Rh:Ir alloyed nanoparticles displayed higher catalytic activity, reaching optimal selectivity and activity at an 8:16–Rh:Ir ratio. The combined catalytic results illustrate that preorganization of the metal complexes in the nanosphere before the reduction with hydrogen effectively facilitates the formation of Rh:Ir alloyed nanoparticles, which allows for tuning a catalyst to create a more active and selective catalyst compared to monometallic or nonencapsulated Rh/Ir particles.