In Crystallo O2 Cleavage at a Preorganized Triiron Cluster

In Nature, the four-electron reduction of O2 is catalyzed at preorganized multimetallic active sites. These complex active sites often feature low-coordinate, redox-active metal centers precisely positioned to facilitate rapid O2 activation processes that obviate the generation of toxic, partially-reduced oxygen species. Very few biomimetic constructs simultaneously recapitu-late the complexity and reactivity of these biological cofactors. Herein, we report solid-state O2 activation at a triiron(II) active site templated by phosphinimide ligands. Insight into the structure of the O2 reduction intermediates was obtained via in crystallo O2 dosing experiments in conjunction with spectroscopic, structural, magnetic, and computational studies. These data support the in situ formation of an Fe2IIIFeIV-dioxo intermediate upon O2 exposure that participates in oxygen atom and hydrogen atom transfer reactivity with exogenous substrates to furnish a stable FeIIFe2III-oxo species. Combined, these stud-ies provide an extraordinary level of detail into the dynamics of bond forming and breaking processes operative at complex multimetallic active sites.