Ligand-Free Ultrasmall Recyclable Iridium(0) Nanoparticles for Regioselective Aromatic Hydrogenation of Phosphine Oxide Scaffolds: An Easy Access to New Phosphine Ligands

Abstract

Herein, we developed the recyclable ligand-free iridium (Ir)-hydride based Ir⁰ nanoparticles (NPs) for the first regioselective partial hydrogenation of P^V -substituted naphthalenes. Both the isolated and in situ generated NPs are catalytically active. A control nuclear magnetic resonance (NMR) study revealed the presence of metal-surface-bound hydrides, most likely formed from Ir⁰ species. A control NMR study confirmed that hexafluoroisopropanol as a solvent was accountable for substrate activation via hydrogen bonding. High-resolution transmission electron microscopy of the catalyst supports the formation of ultrasmall NPs, and X-ray photoelectron spectroscopy confirmed the dominance of Ir⁰ in the NPs. The catalytic activity of NPs is broad as showcased by highly regioselective aromatic ring reduction in various phosphine oxides or phosphonates. The study also showcased a novel pathway toward preparing bis(diphenylphosphino)-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl (H₈ -BINAP) and its derivatives without losing enantioselectivity during catalytic events.

Keywords: Hydrogenation; Iridium; Ligands; Nanoparticles; Phosphine Oxides.