Free Metallophosphines: Extremely Electron-Rich Phosphorus Superbases that are Electronically and Sterically Tunable

A variety of research fields ranging from catalysis to materials science benefit from readily accessible electron-rich ancillary ligands such as phosphines with diverse stereoelectronic properties. We report herein a facile and highly modular access to an intriguing class of free Au-substituted phosphines (AuPhos), namely (LAu)nPR3-n (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 electron-rich d10 Au substituents and the lone pair at P. A series of multi-nuclear transition metal complexes (i.e. Rh, Ir, Au, W, Mn) ligated by AuPhos are readily prepared via a straightforward process. Preliminary catalytic results reveal the facilitation of Ir-catalyzed decarbonylation reactions of aldehydes via AuPhos, unveiling their tremendous potential for the development and improvement of transition metal catalysts when electron-rich metal centers are required.