Installation of internal electric fields by non-redox active cations in transition metal complexes

Kang, Kevin; Fuller, Jack T.; Reath, Alexander H.; Ziller, Joseph W.; Alexandrova, Anastassia N.; Yang, Jenny Y.

doi:10.1039/c9sc02870f

Cited by 69 publications

(86 citation statements)

References 47 publications

(48 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Electric fields are known to play an important role in many catalytic transformations throughout chemistry 1 − 20 and biology. 21 , 22 For example, in molecular catalysis, charged moieties in the secondary sphere of a coordination compound can impart oriented internal electric fields, 11 , 13 − 15 which have been used to accelerate CO 2 activation ( Figure 1 , left). 11 Similarly, in enzymes, amino acid residues sustain enormous oriented electric fields within the active site that can drive biological catalysis ( Figure 1 , center).…”

Section: Introductionmentioning

confidence: 99%

Spontaneous Electric Fields Play a Key Role in Thermochemical Catalysis at Metal−Liquid Interfaces

2021

View full text Add to dashboard Cite

Large oriented electric fields spontaneously arise at all solid–liquid interfaces via the exchange of ions and/or electrons with the solution. Although intrinsic electric fields are known to play an important role in molecular and biological catalysis, the role of spontaneous polarization in heterogeneous thermocatalysis remains unclear because the catalysts employed are typically disconnected from an external circuit, which makes it difficult to monitor or control the degree of electrical polarization of the surface. Here, we address this knowledge gap by developing general methods for wirelessly monitoring and controlling spontaneous electrical polarization at conductive catalysts dispersed in liquid media. By combining electrochemical and spectroscopic measurements, we demonstrate that proton and electron transfer from solution controllably, spontaneously, and wirelessly polarize Pt surfaces during thermochemical catalysis. We employ liquid-phase ethylene hydrogenation on a Pt/C catalyst as a thermochemical probe reaction and observe that the rate of this nonpolar hydrogenation reaction is significantly influenced by spontaneous electric fields generated by both interfacial proton transfer in water and interfacial electron transfer from organometallic redox buffers in a polar aprotic ortho -difluorobenzene solvent. Across these vastly disparate reaction media, we observe quantitatively similar scaling of ethylene hydrogenation rates with the Pt open-circuit electrochemical potential ( E OCP ). These results isolate the role of interfacial electrostatic effects from medium-specific chemical interactions and establish that spontaneous interfacial electric fields play a critical role in liquid-phase heterogeneous catalysis. Consequently, E OCP —a generally overlooked parameter in heterogeneous catalysis—warrants consideration in mechanistic studies of thermochemical reactions at solid–liquid interfaces, alongside chemical factors such as temperature, reactant activities, and catalyst structure. Indeed, this work establishes the experimental and conceptual foundation for harnessing electric fields to both elucidate surface chemistry and manipulate preparative thermochemical catalysis.

show abstract

Section: Introductionmentioning

confidence: 99%

Spontaneous Electric Fields Play a Key Role in Thermochemical Catalysis at Metal−Liquid Interfaces

2021

View full text Add to dashboard Cite

show abstract

“…In homogeneous chemistry, the electrostatic field of certain cationic species can impact the redox behavior of dissolved molecular complexes. 114 Interfacial chemistry in heterogeneous systems is commonly modulated by ionic additives 115 − 117 and electrolyte ions 118 − 120 in various electrocatalytic processes. Such strategies can be extrapolated to framework materials.…”

Section: Discussionmentioning

confidence: 99%

From Molecules to Porous Materials: Integrating Discrete Electrocatalytic Active Sites into Extended Frameworks

et al. 2020

View full text Add to dashboard Cite

Metal–organic and covalent–organic frameworks can serve as a bridge between the realms of homo- and heterogeneous catalytic systems. While there are numerous molecular complexes developed for electrocatalysis, homogeneous catalysts are hindered by slow catalyst diffusion, catalyst deactivation, and poor product yield. Heterogeneous catalysts can compensate for these shortcomings, yet they lack the synthetic and chemical tunability to promote rational design. To narrow this knowledge gap, there is a burgeoning field of framework-related research that incorporates molecular catalysts within porous architectures, resulting in an exceptional catalytic performance as compared to their molecular analogues. Framework materials provide structural stability to these catalysts, alter their electronic environments, and are easily tunable for increased catalytic activity. This Outlook compares molecular catalysts and corresponding framework materials to evaluate the effects of such integration on electrocatalytic performance. We describe several different classes of molecular motifs that have been included in framework materials and explore how framework design strategies improve on the catalytic behavior of their homogeneous counterparts. Finally, we will provide an outlook on new directions to drive fundamental research at the intersection of reticular-and electrochemistry.

show abstract

“…Non-redox active cations of varying charge are easily inserted into the crown cavity which significantly modifies the electric field potential around the redox active metal. 51 Our previous investigation of Mn(V) salen nitrido complexes (1-Na, 1-K, 1-Ba, 1-Sr) with bound alkali and alkaline earth metals showed that an increase of cationic charge at the complexes resulted in anodic shifts of over 400 mV of the Mn(VI/V) reduction potential (Table 1). 52 To expand on these studies, we synthesized two derivatives with +3 cations, so that our data set spans four different units of charge.…”

mentioning

confidence: 92%

Cationic Effects on the Effective Hydrogen Atom Bond Dissociation Free Energy of High Valent Manganese Imido Complexes

Léonard

Chantarojsiri

Yang

2021

Preprint

Self Cite

View full text Add to dashboard Cite

Local electric fields can alter energy landscapes to impart enhanced reactivity in enzymes and at surfaces. There has been renewed interest on their use in molecular systems, where they can be installed using charged functionalities. Manga-nese(V) salen nitrido complexes (salen = N,N’-ethylenebis(salicylideneaminato)) appended with a crown ether unit con-taining a Na+ (1-Na), K+, (1-K), Ba2+ (1-Ba), Sr2+ (1-Sr), La3+ (1-La), or Eu3+ (1-Eu) cation were investigated to experimen-tally demonstrate the effect of cation-induced electric fields on pKa, E1/2, and the effective bond dissociation free energy (BDFE) of N–H bonds. The series, which includes the manganese (V) salen nitrido without a crown appended, spans 4 units of charge. Bounds for the pKa values of the transient imido complexes were determined by UV-visible and 1H NMR spectroscopy. These values, together with the reduction potentials for the Mn(VI/V) couple measured by cyclic voltamme-try in acetonitrile, were used to calculated the N–H BDFEs of the imidos. Despite spanning >700 mV and >9 pKa units across the series, the hydrogen atom BDFE only spans ~ 5 kcal/mol (between 76 and 81 kcal/mol). These results suggest that incorporation of cationic functionalities is an effective strategy for accessing wide ranges of reduction potentials and pKa while minimally affecting BDFE, which is essential to modulating electron, proton, or hydrogen atom transfer path-ways.

show abstract

Installation of internal electric fields by non-redox active cations in transition metal complexes

Abstract: Experimental and computational study quantifying internal electric fields in synthetic systems using transition metal Schiff base complexes functionalized with a crown ether unit containing a mono- or dicationic alkali or alkaline earth metal ion.

Cited by 69 publications

References 47 publications

Spontaneous Electric Fields Play a Key Role in Thermochemical Catalysis at Metal−Liquid Interfaces

Spontaneous Electric Fields Play a Key Role in Thermochemical Catalysis at Metal−Liquid Interfaces

From Molecules to Porous Materials: Integrating Discrete Electrocatalytic Active Sites into Extended Frameworks

Cationic Effects on the Effective Hydrogen Atom Bond Dissociation Free Energy of High Valent Manganese Imido Complexes

Contact Info

Product

Resources

About