Hemilabile Proton Relays and Redox Activity Lead to {FeNO}^x and Significant Rate Enhancements in NO₂^– Reduction

Abstract

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 the enhancements in the initial rate.

A Stable Polyoxometalate-Based Metal–Organic Framework with Active CoMoO4 Layers for Electroreduction and Visible-Light-Driven Water Oxidation

“…The Nyquist plot of SYNU-1 reveals that it possesses the small charge transfer resistance ( R ct ), indicating a fast interfacial charge transfer rate would occur in SYNU-1 (Figure b) . Nitrite and bromate ions are known as potential carcinogens which may lead to significant toxic effects. − Hence, we also studied the electroreduction of nitrite and bromate at SYNU-1 CPE. It remains unchanged for nitrite at the bare CPE.…”

Graphite Conjugation of a Macrocyclic Cobalt Complex Enhances Nitrite Electroreduction to Ammonia

“…Several molecular electrocatalysts have been reported for the reduction of aqueous nitrite. − While many copper and iron complexes have been shown to catalyze nitrite reduction to NO, N 2 O, NH 2 OH, and/or NH 4 + , − selective reduction is challenging, with the product distribution dependent on applied potential, pH, and/or reaction time. − Nonetheless, molecular electrocatalysts having excellent product selectivity have been reported, with a leading example being a CoGGH complex (GGH = Gly-Gly-His model tripeptide), which rapidly reduces nitrite to ammonia with high Faradaic efficiency (∼90%) …”

Requirements for Late-Stage Hydroboration of Pyridine N-Heterocyclic Carbene Iron(0) Complexes: The Role of Ancillary Ligands

“…The IR spectrum (KBr) of 4- t Bu 3 C 6 H 2 resembles that of related dicarbonyl complexestwo well-defined absorptions at 1992 and 1896 cm –1 assigned to CN stretching modes (Figure S69). − The IR absorption profiles of 4-Ph and 4- t Bu (KBr) are more challenging to interpret (Figures S70 and S71). Each displays a combination of weak and strong ill-defined absorptions in the energy range of 2090–1680 cm –1 , and the lower energy vibrations indicate an increased activation of the isocyanide ligands in 4-Ph and 4- t Bu .…”