Ligand-based reduction of nitrate to nitric oxide utilizing a proton-responsive secondary coordination sphere

Abstract

Utilizing the proton-responsive pyridinediimine ligand [(2,6-PrCH)(N[double bond, length as m-dash]CMe)(N(Pr)CH)(N[double bond, length as m-dash]CMe)CHN] (didpa), the ligand-based reduction of nitrate (NO) to nitric oxide (NO) was achieved. The bioinspired [Fe(Hdidpa)(CO)] was shown to react with tetrabutylammonium nitrate to form the dinitrosyl iron complex [Fe(didpa)(NO)]. The didpa scaffold was shown to provide two electrons for the net reduction of NO to NO in 43% yield.

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

“…Similar to the previously reported Fe(didpa)(CO) 2 (didpa = [(2,6- i PrC 6 H 3 )(N=CMe)(N( 1 Pr) 2 C 2 H 4 )(N=CMe)C 5 H 3 N]) complex, 50 3 and 4 both react with two equivalents NO 2 − and four equivalents H + (Scheme 1, middle) yielding the representative dinitrosyl iron complexes (DNICs), [Fe( Pyrr PDI)(NO) 2 ] + ( 5 ) and [Fe( Mor PDI)(NO) 2 ] + ( 6 ). The solid state structures of 5 and 6 are shown in Figure 2.…”

“…41–47 Our group has been active in developing methodologies that control the movement of both protons and electrons for biologically relevant reactions by utilizing the redox-active pyridinediimine (PDI) scaffold merged with a proton-responsive secondary coordination sphere. 48–50 Those preliminary studies successfully showed: 1) the PDI scaffold can be tailored to facilitate NO 2 − reduction, and; 2) the NO 2 − reduction is dependent on the protonation state of the secondary coordination sphere (proton-responsivity). Furthermore, given the revelations of the role ligand hemilability plays in biomimicry, 51–53 we reasoned that the pendant base(s) could be utilized to introduce hemilability into the PDI, yielding ligand scaffolds that increase activity even further.…”

A flexible, redox-active macrocycle enables the electrocatalytic reduction of nitrate to ammonia by a cobalt complex

“…However there are few examples of molecular electrocatalysts for nitrate reduction, 25 – 29 and very little is known about their reaction mechanisms. While a number of examples of stoichiometric conversions of nitrate by homogeneous metal complexes suggest the importance of hydrogen donor functionalities for nitrate activation, 30 , 31 these results do not provide guidelines for designing electrocatalysts that are selective for nitrate reduction.…”

Uncoupled Redox-Inactive Lewis Acids in the Secondary Coordination Sphere Entice Ligand-Based Nitrite Reduction

“…These integrated (yet uncoupled) complexes are capable of storing both protons and electrons for transfer to substrate. 71,72…”