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

Herein, we developed the recyclable ligand-free iridium (Ir)-hydride based Ir-0 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 Ir-0 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 Ir-0 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 & PRIME;,6,6 & PRIME;,7,7 & PRIME;,8,8 & PRIME;-octahydro-1,1 & PRIME;-binaphthyl (H-8-BINAP) and its derivatives without losing enantioselectivity during catalytic events.

Automated summary

In this study, recyclable ligand-free iridium (Ir)-hydride based Ir-0 nanoparticles (NPs) were developed for the selective partial hydrogenation of P-V-substituted naphthalenes. Both isolated and in situ generated NPs showed catalytic activity. Metal-surface-bound hydrides were observed in the NMR study, likely formed from Ir-0 species. Hexafluoroisopropanol as a solvent was found to activate the substrate through hydrogen bonding. The highly regioselective aromatic ring reduction was demonstrated in different phosphine oxides or phosphonates using the NPs as catalysts. The study also presented a novel approach for preparing H-8-BINAP and its derivatives without losing enantioselectivity during catalytic events.