Proton-coupled reduction of an iron nitrosyl porphyrin in the protic ionic liquid nanodomain

Abstract

The one-electron reduction of many molecules becomes much more favorable if combined with proton transfers or strong hydrogen bonding. Protic room temperature ionic liquids (RTILs), which can form nanodomains in solutions with molecular solvents (MS), can provide an efficient avenue for this process. In this work, we report on the voltammetry, UV/visible and resonance Raman spectroelectrochemistryof Fe(TPP)(NO) in the presence of aprotic/protic ammonium-based ionic liquids. While aprotic RTILs did shift the reduction to more positive potentials, similar shifts could be observed at much lower concentrations of diethylmethylammonium triflate (HAmOTf, a protic ionic liquid). Deconvolution of the rotating ringdisk electrode (RRDE) voltammetry revealed the partitioning of the reduced species into the ionic liquid nanodomains at low concentrations. The potential shift was substantially in excess of the value expected based on the pKa of the weak acid. Upon the addition of small amounts of the protic RTIL, the electrochemically or chemically generated anion, Fe(TPP)(NO)-, reacted rapidly with the HAm + acid, forming a Fe(TPP)(HNO) complex. Further reduction to Fe(TPP)(NH2OH) could be observed on the spectroelectrochemical time scale. The outcome of this work revealed the advantageous role of protic RTIL nanodomains in accelerating the proton-coupled reductions to form more energetically favorable product.

Water Interplays during Dysprosium Electrodeposition in Pyrrolidinium Ionic Liquid: Deconvoluting the Pros and Cons for Rare Earth Metallization

“…These observations are consistent with Dy partitioning between water-coordinated and IL-coordinated speciation. A similar impact of ionic liquids solvation and coordination on the redox behavior of organic and inorganic systems and their implications in many electrochemical processes have been extensively reported by Atifi et al − At an equimolar fraction, the water molecules would be partially coordinated to the Dy complex (Red1), with an important fraction remaining as free or weakly coordinated molecules. Increasing the metal loading (or lowering x H 2 O ) increased the fraction of metal-coordinated water (Dy-H 2 O) at the expense of free or weakly coordinated water (IL-coordinated complex), resulting in a rise of Red1 at the expense of Red2.…”

Reversible Proton-Coupled Reduction of an Iron Nitrosyl Porphyrin within [DBU–H]+-Based Protic Ionic Liquid Nanodomains

“…This approach was leveraged by Rosen et al, 18 who used a room-temperature ionic liquid (RTIL) promoter for CO 2 reduction at silver cathodes. Since then, several other researchers have studied the use of RTILs to promote the reduction of coordinated nitrosyls 6 or CO 2 . 19−28 In particular, the efficient catalysis of CO 2 to CO was reported using a bismuth film electrode and ionic liquids, 25,26,28 and similar catalysis was carried out in acetonitrile/imidazolium-based electrolyte mixtures using thin CuSn films.…”

Voltammetry and Spectroelectrochemistry of TCNQ in Acetonitrile/RTIL Mixtures

“…Generally, the difference between the waves (∆E 12 • = E 1 • − E 2 • , where 1 and 2 are sequential redox couples) was smaller for RTILs as compared to molecular solvents, due to the increased solvation of the more negatively charged species. The variation in the ∆E 12 • values as a function of %RTIL has been studied for several substrates by Atifi and Ryan [2,[4][5][6][7] and others [8].…”

“…The substrate can partition between these two nanodomains. Within each nanodomain, the solute will experience different solvation interactions and reactivity [7]. There are also structural heterogeneities within the RTIL itself, where there are more polar regions containing the anion and less polar regions where the alkyl side chains reside [13].…”