Hemilabile Proton Relays and Redox Activity Lead to {FeNO}<sup><i>x</i></sup> and Significant Rate Enhancements in NO<sub>2</sub><sup>–</sup> Reduction
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Incorporation of the triad of redox activity, hemilability, and proton responsivity into a single ligand scaffold is reported. Due to this triad, the complexes Fe(PyrrPDI)(CO)2 (3) and Fe(MorPDI)(CO)2 (4) display 40-fold enhancements in the initial rate of NO2– reduction, with respect to Fe(MeOPDI)(CO)2 (7). Utilizing the proper sterics and pKa of the pendant base(s) to introduce hemilability into our ligand scaffolds, we report unusual {FeNO}x mononitrosyl iron complexes (MNICs) as intermediates in the NO2– reduction reaction. The {FeNO}x species behave spectroscopically and computationally similar to {FeNO}7, an unusual intermediate-spin Fe(III) coupled to triplet NO– and a singly reduced PDI ligand. These {FeNO}x MNICs facilitate enhancements in the initial rate.
