"Weakly Ligated, Labile Ligand" Nanoparticles: The Case of Ir(0) ·(H⁺Cl^-)

It is of considerable interest to prepare weakly ligated, labile ligand (WLLL) nanoparticles for applications in areas such as chemical catalysis. WLLL nanoparticles can be defined as nanoparticles with sufficient, albeit minimal, surface ligands of moderate binding strength to meta-stabilize nanoparticles, initial stabilizer ligands that can be readily replaced by other, desired, more strongly coordinating ligands and removed completely when desired. Herein, we describe WLLL nanoparticles prepared from [Ir(1,5-COD)Cl]₂ reduction under H₂, in acetone. The results suggest that H⁺Cl^--stabilized Ir(0) nanoparticles, herein Ir(0) ·(H⁺Cl^-) , serve as a WLLL nanoparticle for the preparation of, as illustrative examples, five specific nanoparticle products: Ir(0) ·(Cl^-Bu₃NH⁺) , Ir(0) ·(Cl^-Dodec₃NH⁺) , Ir(0) ·(POct₃)_0.2 (Cl^-H⁺) , Ir(0) ·(POct₃)_0.2 , and the γ-Al₂O₃-supported heterogeneous catalyst, Ir(0) ·(γ-Al₂O₃) (Cl^-H⁺) . (where a and b vary for the differently ligated nanoparticles; in addition, solvent can be present as a nanoparticle surface ligand). With added POct₃ as a key, prototype example, an important feature is that a minimum, desired, experimentally determinable amount of ligand (e.g., just 0.2 equiv POct₃ per mole of Ir) can be added, which is shown to provide sufficient stabilization that the resultant Ir(0) ·(POct₃)_0.2 (Cl^-H⁺) is isolable. Additionally, the initial labile ligand stabilizer HCl can be removed to yield Ir(0) ·(POct₃)_0.2 that is >99% free of Cl^- by a AgCl precipitation test. The results provide strong support for the weakly ligated, labile ligand nanoparticle concept and specific support for Ir(0) ·(H⁺Cl^-) as a WLLL nanoparticle.