Switching the Electron-Donating Ability of Phosphines through Proton-Responsive Imidazolin-2-ylidenamino Substituents.

Stimuli-responsive ancillary ligands are valuable tools to control the activity and selectivity of transition-metal catalysts. The synthesis and characterization of a series of metal complexes containing phosphines with proton-responsive imidazolin-2-ylidenamino substituents are reported. Determination of the ligand-donor properties revealed that protonation of each substituent increases the Tolman electronic parameter (TEP) of the phosphine by 22 cm-1 , hence allowing for switching of the electron-donor power of phosphine 2 within an unprecedented range (ΔTEP=43.4 cm-1 ).