Synthesis of Heterogeneous Ir0∼600–900/γ-Al2O3 in One Pot From the Precatalyst Ir(1,5-COD)Cl/γ-Al2O3: Discovery of Two Competing Trace “Ethyl Acetate Effects” on the Nucleation Step and Resultant Product

Abstract

In 2010 we reported a two-step synthesis of a Ir0∼900/γ-Al2O3 supported-nanoparticle catalyst. In that study, a well-defined Ir(1,5-COD)Cl/γ-Al2O3 precatalyst was isolated and characterized before being reduced in contact with acetone solvent and cyclohexene and under H2 in a second step. Synthetically, one would like to remove the Ir(1,5-COD)Cl/γ-Al2O3 precatalyst isolation step, shortening the precatalyst synthesis and allowing the overall synthesis to be accomplished more efficiently in one pot. However, herein we report that the one-pot synthesis starting from commercially available [Ir(1,5-COD)Cl]2 and γ-Al2O3 yields an order of magnitude increase in the observed nucleation rate constant, k1,obs, as well as a decrease in the average particle size from Ir0∼900 to Ir0∼600. Mechanistic experiments reveal that the origin of this effect, amazingly, is the presence of residual ethyl acetate employed in the isolated precatalyst synthesis, which is not present in the one-pot synthesis. Additional mechanistic...