Dylan G. Boucher’s research while affiliated with University of Utah and other places

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Publications (23)


Electrolyte Cage Effects in Organic Electrosynthesis: Measuring and Driving Selectivity
  • Article

November 2024

ECS Meeting Abstracts

Zachary A Nguyen

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Dylan G. Boucher

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Kevin McFadden

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Shelley Minteer

Electrochemical organic synthesis shows promise for the sustainable synthesis of agrochemical and pharmaceutically relevant molecules. However, the complexity of integrating organic and electrochemical methods often leads to overlooked reaction parameters. For example, electrolyte salts are used to decrease resistivity of the electrochemical cell and are traditionally viewed as benign species in electrochemical systems. However, the electroorganic literature is filled with examples in which changing the identity of the electrolyte impacts the reaction selectivity significantly, implying that these ‘benign’ molecules have overlooked chemical contributions to reactivity, such as the stabilization of critical intermediates. Here, we explore the impact of electrolyte species on an important class of organic reactions: organic bond homolysis. In this reaction, a cage-paired radical is formed through the homolytic cleavage of a carbon bond, which then exists in a shell of solvent and solvated salts. This solvent-ion shell can stabilize this intermediate and allow for reversible bond homolysis. Such caged species are well-studied phenomena in metal-hydrogen atom transfer reactions and have been demonstrated to directly influence product selectivity in various organic reactions such as hydrogenation, isomerization, and dimerization. Here, we focus on how the lifetimes of cage-paired metal alkyl radical species are affected by common organic electrolytes and how this lifetime informs product selectivity. The lifetimes of these caged intermediates in various electrolyte conditions were examined using cyclic voltammetry, where titration studies were conducted to determine the rate of escape from the solvent-ion cage. This study provides insight into the role of common electrolyte salts on the stability of caged metal alkyl species and subsequent selectivity in organic synthetic reactions.


Non-Native Bioelectrocatalytic C-C and C-N Bond Formation via Cobalamin Dependent Enzymes

November 2024

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2 Reads

ECS Meeting Abstracts

Luke Kays

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Dylan G. Boucher

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[...]

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Shelley D. Minteer

Bioelectrocatalysis involves the use of biomaterials to catalyze redox reactions at an electrode. Biocatalysis offers improved selectivity and typically involves milder reaction conditions, while electrocatalysis can involve the use of renewable energy as an electron source. Cobalamin (B 12 ) dependent enzymes catalyze C-C and C-N bond forming reactions via radical mechanisms through the formation of a Co(III)-alkyl intermediate. Homolysis of the Co(III)-C bond leads to radical coupling with various substrates to form the product. However, these alkyl radicals can react through a variety of mechanistic pathways, leading to a mixture of products. Controlling the alkyl radical intermediate would lead to improved reaction selectivity. Here, we report on CarH*, an engineered variant of a B 12 dependent photoreceptor protein, which catalyzes styrene C-H alkylation by trapping an alkyl radical intermediate in its protein scaffold. The reversible Co-alkyl bond homolysis protects the radical, allowing for selective olefin addition. However, to initiate this reactivity, the cobalt center of CarH* must be reduced through stoichiometric addition of the reducing agent titanium (III) citrate. Thus, we are developing a mediated electrochemical system to achieve this transformation without the use of a stoichiometric reductant and to investigate new reactivity in CarH* and similar variants. A diffusive redox mediator was found to deliver electrons to CarH* and drive alkyl radical formation. This methodology offers a more sustainable and general approach to electrochemical non-native biocatalysis and can be applied to discover new reactivity in B 12 dependent enzymes.


Autonomous and Closed-Loop Exploration and Optimization of Bioelectrocatalytic Systems

November 2024

ECS Meeting Abstracts

Automated electrochemistry platforms provide a pathway for speeding up the discovery and optimization of electrochemical systems, especially when a broad range of molecules and reaction conditions must be explored. ¹⁻³ Additionally, incorporation of machine learning enables closed-loop optimization campaigns, where the obtained experimental data guides the selection of the next set of experimental parameters to test. This type of autonomous exploration is ideally suited for the study of enzyme electrocatalysis, as the combinatorics of different enzymes, substrates, and redox mediators creates a prohibitively large parameter space. Even within a single enzyme class, mutations to the amino acid sequence can significantly impact rate, function, and selectivity of the catalyzed reaction. Thus, an automated electrochemical platform that enables rapid sampling both reaction parameters and amino acid sequence space would enable discovery of new, non-native enzymatic reactions. In this work we use an open source and modular automated electrochemistry platform to study enzyme electrocatalysis in several common bioelectrocatalytic systems, such as glucose oxidase, glucose dehydrogenase, and aldehyde dehydrogenase. We use automated cyclic voltammetric substrate titration experiments (Figure 1) to gain insight into the kinetics of the redox-mediated enzymatic catalysis and demonstrate the reaction conditions in which traditional mechanistic simplifications, like Michaelis-Menten, break down. Additionally, the automated electrochemistry platform allows for the rapid screening of different substrate molecules, enabling the quantification of substrate promiscuity in these enzymatic catalysts. We show how Bayesian Optimization can be incorporated into our workflow to autonomously tune solution parameters to promote increased reaction rates. These studies demonstrate the power of autonomous electrochemistry for understanding and screening biocatalytic systems and represent a significant step towards totally machine-guided biocatalyst evolution. [1] Oh, I. ; Pence, M. A.; Lukhanin, N.; Rodriguez, O.; Schroeder, C. M.*; Rodriguez-Lopez, J.*, “The Electrolab: An open-source, modular platform for automated characterization of redox-active electrolytes” Device, 2023, 1 , 5, 100103 [2] Rodriguez, O.; Pence, M. A.; Rodriguez-Lopez, J.*, “Hard Potato: An Open Source Python Library to Control Commercially Available Potentiostats and Automate Electrochemical Experiments” Anal. Chem., 2023, 95 , 4840–4845 [3]Pence, M. A.; Rodriguez, O.; Lukhanin, N.; Schroeder, C. M.*; Rodriguez-Lopez, J.*, “Automated Measurement of Electrogenerated Redox Species Degradation Using Multiplexed Interdigitated Electrode Arrays”, ACS Meas. Sci. Au, 2023, 3, 62–72 Figure 1


Measuring Hydride Transfer Kinetics to Mhat Relevant Catalysts Using Cyclic Voltammetry

November 2024

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2 Reads

ECS Meeting Abstracts

The area of organic electrocatalysis has been growing in importance as many new transformations have been developed and previously known transformations are adapted to be accomplished electrochemically. As the field of synthetic organic electrochemistry emerges, it is becoming ever more important to study the mechanisms of these electrocatalytic reactions. Understanding the mechanics of the chemical processes and how they are coupled to the electrode is critical for continuing to expand the synthetic utility of electrocatalysis. Radical based hydrofunctionalization of alkenes through transition-metal catalyzed hydrogen atom transfer (MHAT) mechanisms is a proven, powerful mode of forming C−C, C−O, C−N and C−X bonds. In recent years, new asymmetric MHAT reactions have been enabled through electrocatalysis. The in situ generation of the key metal-hydride species plays a crucial role in both the kinetics and selectivity of the observed products. These high energy metal hydrides are too reactive and too short lived to be isolated, thus the oxidative mechanism leading to their formation is poorly understood. Here, we utilize a model catalytic cycle in which metal hydride formation is the rate determining step. Cyclic voltammetry enables us to extract the rate constant of hydride transfer. The differences in kinetic trends between catalysts and hydride donors indicate separate mechanisms of hydride transfer are operative for different classes of MHAT catalysts. Specific trends in ligand electronics, hydride donor sterics and hydricity for cobalt salen type catalysts allowed us to postulate a possible metal/ligand cooperative mechanism of hydride transfer. In summary, these studies represent a significant step towards understanding the homolytic reactivity of metal hydride species and will help enable the design of new electrosynthetic reactions involving radical intermediates.


Figure 3. Cyclic voltammograms for a range of TEMPO derivatives with different structures (R groups) illustrating the relationship between the differences in R groups, oxidizing activity, and reversibility. (A) acetamido-TEMPO (ACT, green traces), (B) methoxy-TEMPO (MT, orange traces), (C) TEMPO (T, yellow traces), (D) hydroxy-TEMPO (HT, blue traces), (E) oxo-TEMPO (OT, purple traces), and (F) amino-TEMPO (AT, red traces). CVs obtained in a 0.5 M borate buffer solution (pH 9.2) containing 1 mM of varying TEMPO catalysts at scan rates 10 mV/s−1 V/s.
Figure 4. Cyclic voltammograms of (A) acetamido-TEMPO (ACT, green traces), (B) methoxy-TEMPO (MT, orange traces), (C) TEMPO (T, yellow traces), (D) hydroxy-TEMPO (HT, blue traces), (E) oxo-TEMPO (OT, purple traces), and (F) amino-TEMPO (AT, red traces) in the presence of increasing BHMF concentrations. CVs obtained in a 0.5 M borate buffer solution (pH 9.2) containing 1 mM of varying TEMPO catalysts at scan rate 10 mV/s.
Figure 5. Bulk electrolysis i−t trace for BHMF oxidation to FDCA, catalyzed by ACT. 10 mM BHMF, 1 mM ACT. Borate buffer pH 9.2.
Figure 6. Bulk electrolysis traces for the oxidation of 10 mM BHMF catalyzed by 1 mM of various TEMPO catalysts in borate buffer solution (pH 9.2). (A) acetamido-TEMPO (ACT, green traces), (B) methoxy-TEMPO (MT, orange traces), (C) TEMPO (T, yellow traces), (D) hydroxy-TEMPO (HT, blue traces), (E) oxo-TEMPO (OT, purple traces), and (F) amino-TEMPO (AT, red traces).
Figure 7. Oxidized products of BHMF highlighting the desired product, FDCA.

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Improved Electrosynthesis of Biomass Derived Furanic Compounds via Nitroxyl Radical Redox Mediation
  • Article
  • Full-text available

June 2024

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48 Reads

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1 Citation

Chem & Bio Engineering

Biomass is an abundantly available, underutilized feedstock for the production of bulk and fine chemicals, polymers, and sustainable and biodegradable plastics that are traditionally sourced from petrochemicals. Among potential feedstocks, 2,5-furan dicarboxylic acid (FDCA) stands out for its potential to be converted to higher-value polymeric materials such as polyethylene furandicarboxylate (PEF), a bio-based plastic alternative. In this study, the sustainable, electrocatalytic oxidation of stable furan molecule 2,5-bis(hydroxymethyl)furan (BHMF) to FDCA is investigated using a variety of TEMPO derivative electrocatalysts in a mediated electrosynthetic reaction. Three TEMPO catalysts (acetamido-TEMPO, methoxy-TEMPO, and TEMPO) facilitate full conversion to FDCA in basic conditions with >90% yield and >100% Faradaic efficiency. The remaining three TEMPO catalysts (hydroxy-TEMPO, oxo-TEMPO, and amino-TEMPO) all perform intermediate oxidation of BHMF in basic conditions but do not facilitate full conversion to FDCA. On the basis of pH studies completed on all TEMPO derivatives to assess their electrochemical reversibility and response to substrate, pH and reversibility play significant roles in the catalytic ability of each catalyst, which directly influences catalyst turnover and product formation. More broadly, this study also highlights the importance of an effective and rapid electroanalytical workflow in mediated electrosynthetic reactions, demonstrating how voltammetric catalyst screening can serve as a useful tool for predicting the reactivity and efficacy of a catalyst–substrate electrochemical system.

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Advanced Electroanalysis for Electrosynthesis

November 2023

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179 Reads

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8 Citations

ACS Organic & Inorganic Au

Electrosynthesis is a popular, environmentally friendly substitute for conventional organic methods. It involves using charge transfer to stimulate chemical reactions through the application of a potential or current between two electrodes. In addition to electrode materials and the type of reactor employed, the strategies for controlling potential and current have an impact on the yields, product distribution, and reaction mechanism. In this Review, recent advances related to electroanalysis applied in electrosynthesis were discussed. The first part of this study acts as a guide that emphasizes the foundations of electrosynthesis. These essentials include instrumentation, electrode selection, cell design, and electrosynthesis methodologies. Then, advances in electroanalytical techniques applied in organic, enzymatic, and microbial electrosynthesis are illustrated with specific cases studied in recent literature. To conclude, a discussion of future possibilities that intend to advance the academic and industrial areas is presented.


Electrocatalytic Asymmetric Nozaki–Hiyama–Kishi Decarboxylative Coupling: Scope, Applications, and Mechanism

November 2023

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25 Reads

The first general enantioselective alkyl-Nozaki-Hiyama-Kishi (NHK) coupling reactions are disclosed herein by em-ploying a Cr-electrocatalytic decarboxylative approach. Using easily accessible aliphatic carboxylic acids (via redox-active esters) as alkyl nucleophile synthons, in combination with aldehydes and enabling additives, chiral secondary alcohols are produced in good yield and high enantioselectivity under mild reductive electrolysis. This reaction, which cannot be mimicked using stoichiometric metal or organic reductants, tolerates a broad range of functional groups, and is successfully applied to dramatically simplify the synthesis of multiple medicinally relevant structures and natural products. Mechanistic studies revealed that this asymmetric alkyl e-NHK reaction was enabled by using catalytic tetrakis(dimethylamino)ethylene (TDAE) , which acts as a key reductive mediator to mediate the electrore-duction of the CrIII/chiral ligand complex.



Citations (12)


... TEMPOH may be oxidized at the electrode to TEMPO or engage in comproportionating with TEMPO + to complete the catalytic cycle. 38,[52][53][54] The use of the 16-port fluidic switching valve enabled us to screen 6 substrates molecules in one experimental run with no human intervention. We examined a substrate scope consisting of isopropanol, ethanol, acetaldehyde, trifluoroethanol, ethylene glycol, and glycerol (Scheme 1). ...

Reference:

An automated electrochemistry platform for studying pH-dependent molecular electrocatalysis
Improved Electrosynthesis of Biomass Derived Furanic Compounds via Nitroxyl Radical Redox Mediation

Chem & Bio Engineering

... [18] In 2024, they used the Cr-electrocatalytic decarboxylative method in an enantioselective alkyl-NHK coupling reaction. [19] The electrochemical NHK area within the electroreductive technique enables a more sustainable approach to the NHK reaction. Photocatalysis is a powerful method for generating radicals, [20] radicals can be obtained through Single Electron Transfer (SET), Energy Transfer (ET), Hydrogen Atom Transfer (HAT), Halogen Atom Transfer (XAT), decarboxylation etc. ...

Electrocatalytic Asymmetric Nozaki-Hiyama-Kishi Decarboxylative Coupling: Scope, Applications, and Mechanism
  • Citing Article
  • February 2024

Journal of the American Chemical Society

... However, homogenous catalytic systems are difficult to recycle, and nitrogenase is environmentally sensitive and costly. Immobilization techniques offer potential for improving the performance of tandem chemocatalytic and/or biocatalytic systems 14 . Indeed, hydrogels 15 and metal-organic frameworks (MOFs) 16 have been used to immobilize enzymes for bioelectrocatalysis reactions although they have not yet been demonstrated on tandem catalytic systems involving biocatalysts. ...

Bioelectrocatalysis for Synthetic Applications: Utilities and Challenges
  • Citing Article
  • February 2024

Current Opinion in Electrochemistry

... 7,11−13 Two major challenges in developing new electroorganic reaction schemes are (i) optimizing reaction conditions to achieve the highest yield while requiring the lowest amount of auxiliary reagents and energy input and (ii) developing a suite of analytical methodologies to study complicated reaction mechanisms at the molecular scale with precision. 14,15 For the most ideal reaction conditions, research efforts mainly focus on parameters in the solution phase, such as temperature, solvent/supporting electrolyte composition, and molecular electrocatalysts, to increase the yield of the reaction and induce desired regio-and stereoselectivity. 11,13 As such, homogeneous electrocatalysis has been heavily studied in organic electrochemistry as it enhances the rate of the reaction and decreases the applied electrochemical potential needed to drive the reaction of interest, thereby reducing costs and increasing the efficiency of the desired reaction. ...

Advanced Electroanalysis for Electrosynthesis

ACS Organic & Inorganic Au

... One key advantage is the ability to perform selective transformations, allowing for precise control over reaction pathways and product formation. This selectivity is particularly valuable in complex molecule synthesis and pharmaceutical manufacturing, where the synthesis of specific stereoisomers or functional groups is crucial [31]. Additionally, electro-organic synthesis often operates under milder reaction conditions, reducing the need for harsh chemicals and energy-intensive processes, which aligns well with green chemistry principles. ...

Selective organic electrosynthesis: general discussion
  • Citing Article
  • October 2023

Faraday Discussions

... Metal salen (MSalen) complexes are a ubiquitous molecular electrocatalyst which is capable of a diverse set of reactions, benzyl halide reduction, [4] metal-hydrogen atom transfer, [5] CO 2 reduction, [6] and fuel cell relevant reactions (ORR, OER, H 2 O reduction). Salen ligands are prepared through the condensation of two salicylaldehydes and an ethylene diamine and can vary in the functionalization of the salicylaldehyde and diamine. ...

Unraveling Hydrogen Atom Transfer Mechanisms with Voltammetry: Oxidative Formation and Reactivity of Cobalt Hydride
  • Citing Article
  • August 2023

Journal of the American Chemical Society

... Conventional MES reactors typically employ the biocathode strategy, where a biofilm is affixed to the cathode. In this setup, microorganisms utilize electrons from the cathode to catalyze the reduction of CO 2 , while inert electrodes, commonly used as cathodes, lack the capability to reduce CO 2 themselves [21]. Theoretically, this technology holds significant promise as an innovative approach to actively mitigate carbon emissions [22,23]. ...

Bioelectrocatalytic Synthesis: Concepts and Applications
  • Citing Article
  • July 2023

Angewandte Chemie

... A comparison of microbial and enzymatic e-BNF was recently reviewed by Wang et al. [153] Bioelectrochemical nitrogen fixation was first proposed by Rago and co-workers in a 2019 study where a biofilm of autotrophic nitrogen-fixing microbes (diazotrophs) was subjugated to an applied potential (-0.7 V vs. SHE) for biomass synthesis. [154] In this system, a combination of direct and indirect electron transfer (possibly via external redox proteins and interspecies ET, organic redox mediators, or hydrogen) allowed electrons to be shuttled from the cathode to the nitrogenase complex in the microbial community to fix N2 and inorganic carbon. This applied potential and mixed microbial community biofilm resulted in increased biomass production (18-fold) compared to experimental systems kept at open circuit potential and introduced the new field of e-BNF that combines nitrogen and carbon fixation. ...

Bioelectrocatalytic Synthesis: Concepts and Applications

... This consideration is of prime importance, especially for implementation in industrial processes which require high current densities and might necessitate adaptability to variable operating current densities to adjust to the electricity surplus generated by renewable energy sources. 49,58 Interestingly, supporting salt ion effects were also recently shown for homogeneous electrosynthetic routes such as the catalytic reduction of benzyl chloride with metal tetraphenylporphyrin. 59 The hydrodynamic radius of the supporting salt cation (Li + , TMA + or TBA + ) modulates the stability of the metal-alkyl intermediate involved. For large cations such as TBA + , the charged intermediate is efficiently stabilized by the so solvent-ion shell surrounding it. ...

Exploring Electrolyte Effects on Metal-Alkyl Bond Stability: Impact and Implications for Electrosynthesis

Faraday Discussions

... [50] Based on prior work and our own findings we tentatively present the following catalytic cycle for the generation of the phenonium ion intermediate (Figure 2). The combination of cobalt(II)-salen catalyst A, silane, and Me 3 NFPY · BF 4 is proposed to generate a transient Co III À H species B and a cationic Co III complex C. [51] Hydrogen atom transfer from the metal hydride (MHAT) to the olefin 1 b would generate a carbon-centred radical solvent-caged with the Co II catalyst A. [52] At this stage cage collapse would form organocobalt(III) complex D, which appears to resist rearrangement. Subsequent, single electron oxidation (SEO) of the alkylCo(III) species D could be effected by the cationic Co III complex C or by the excess of oxidant. ...

Unraveling Hydrogen Atom Transfer Mechanisms with Voltammetry: Oxidative Formation and Reactivity of Cobalt Hydride