Free Metallophosphines: Extremely Electron-Rich Phosphorus Superbases That Are Electronically and Sterically Tunable.

We report herein a facile and highly modular access to an intriguing class of free Au-substituted phosphines (AuPhos), namely (LAu) PR (L=singlet carbene ligand; R=H, aryl, alkyl, silyl) (n=1-3). The Tolman electronic parameter (TEP) values coupled with theoretical investigations showcase that Au-substitution can boost the electron-releasing ability of AuPhos, thus leading to an electronically and sterically tunable, extremely electron-rich phosphorus center. The high basicity of AuPhos is attributed to the d-p lone pair π-repulsion arising from interaction between Au substituents and the lone pair at P. A series of multi-nuclear transition metal complexes (i.e. Rh, Ir, Pd, Au, W, Mn) ligated by AuPhos are readily prepared via a straightforward process. Preliminary catalytic results reveal the facilitation of Pd-catalyzed C-N coupling reactions and Ir-catalyzed decarbonylation reactions via AuPhos. This work provides insights for future development of electron-rich ligands.