Multielectron Bond Cleavage Processes Enabled by Redox-Responsive Phosphinimide Ligands

The activation of small molecules via multi-electron redox processes offers promise in mediating difficult transformations related to energy conversion processes. While molecular systems that engage in one- and two-electron redox processes are widespread, those that participate in the direct transfer of four or more electrons to small molecules are very rare. To that end, we report a mononuclear chromium(II) complex competent for the 4-electron reduction of dioxygen (O2) and nitrosoarenes. These systems additionally engage in facile two-electron group transfer reactivity including O-atom excision and nitrene transfer. Structural, spectroscopic and computational studies support bond activation processes that intimately occur at a mononuclear chromium(phosphinimide) center and highlight an unusual structural responsiveness of the phosphinimides in stabilizing a range of metal redox states.