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Peacock H, Blum SA. Buildup and Consumption of Species in Emulsion Droplets during Aqueous Suzuki Coupling Correlate with Yield. J Org Chem 2024; 89:10684-10692. [PMID: 39016689 DOI: 10.1021/acs.joc.4c00918] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/18/2024]
Abstract
Fluorescence lifetime imaging microscopy (FLIM) provides spatiotemporal resolution of the changing composition of emulsion droplets during aqueous-surfactant Suzuki coupling. In contrast to previous investigations, the present experiments characterize the full course of a catalytic chemical reaction, addressing key questions about reaction species buildup and correlating these microscale behaviors with bench-scale product yields. At low concentrations of (active) catalyst, droplet environments are stable; however, at higher concentrations, emulsion droplet environments change markedly. These changes are consistent with the buildup and consumption of reaction species inside the droplets. A combination of FLIM and bright-field imaging pinpoints limitations in catalyst solubility as controlling rate and degree of buildup of species in droplets. These solubility limitations are also identified as the cause of a reaction induction period and an origin of the rate-and-reproducibility advantage obtained by adding THF cosolvent. The subsequent mechanistic model from these data led to a bench-scale reaction optimization, wherein premixing the catalyst components bypasses the catalyst induction period, resulting in a faster reaction. The understanding generated by FLIM thus provides an early example of how visualizing changes in droplet compositions on the microscale during ongoing aqueous-organic reactions can be leveraged for enhancing efficiencies in bench-scale reactions.
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Affiliation(s)
- Hannah Peacock
- Department of Chemistry, University of California, Irvine, Irvine, California 92697-2025, United States
| | - Suzanne A Blum
- Department of Chemistry, University of California, Irvine, Irvine, California 92697-2025, United States
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Hanada EM, Lou H, McShea PJ, Blum SA. Metal Activation Produces Different Reaction Environments for Intermediates during Oxidative Addition. Chemistry 2024; 30:e202304105. [PMID: 38109441 DOI: 10.1002/chem.202304105] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2023] [Revised: 12/16/2023] [Accepted: 12/18/2023] [Indexed: 12/20/2023]
Abstract
Commercial zinc metal powder requires activation for consistent and reliable use as a reductant in the formation of organozinc reagents from organohalides, and for the avoidance of supplier and batch-to-batch variability. However, the impact of activation methods on the reaction environments of subsequent intermediates has been unknown. Herein, a fluorescence lifetime imaging microscopy (FLIM) method is developed to bridge this knowledge gap, by imaging and examining reaction intermediates on zinc metal that has been activated by pretreatment through different common methods (i. e., by chemical activation with TMSCl, dibromoethane, or HCl; or by mechanical activation). The group of chemical activating agents, previously thought to act similarly by removing oxide layers, are here shown to produce markedly different reaction environments experienced by subsequent oxidative-addition intermediates from organohalides - data uniquely available through FLIM's ability to detect small quantities of intermediates in situ coupled with its microenvironmental sensitivity. These different microenvironments potentially give rise to different rates of formation, subsequent solubilization, and reactivity, despite the shared "[RZnX]" molecular structure of these intermediates. This information revises models for methods development for oxidative addition to currently sluggish metals beyond zinc by establishing diverse outcomes for pretreatment activation methods that were previously considered similar.
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Affiliation(s)
- Erin M Hanada
- Chemistry Department, University of California, Irvine, Irvine, CA, 92697-2025, USA
| | - Hanyun Lou
- Chemistry Department, University of California, Irvine, Irvine, CA, 92697-2025, USA
| | - Patrick J McShea
- Chemistry Department, University of California, Irvine, Irvine, CA, 92697-2025, USA
| | - Suzanne A Blum
- Chemistry Department, University of California, Irvine, Irvine, CA, 92697-2025, USA
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Hanada EM, McShea PJ, Blum SA. Trimethylsilyl Chloride Aids in Solubilization of Oxidative Addition Intermediates from Zinc Metal. Angew Chem Int Ed Engl 2023; 62:e202307787. [PMID: 37672719 PMCID: PMC10591914 DOI: 10.1002/anie.202307787] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2023] [Revised: 08/26/2023] [Accepted: 09/06/2023] [Indexed: 09/08/2023]
Abstract
Trimethylsilyl chloride (TMSCl) is commonly used to "activate" metal(0) powders toward oxidative addition of organohalides, but knowledge of its mechanism remains limited by the inability to characterize chemical intermediates under reaction conditions. Here, fluorescence lifetime imaging microscopy (FLIM) overcomes these prior limitations and shows that TMSCl aids in solubilization of the organozinc intermediate from zinc(0) metal after oxidative addition, a previously unknown mechanistic role. This mechanistic role is in contrast to previously known roles for TMSCl before the oxidative addition step. To achieve this understanding, FLIM, a tool traditionally used in biology, is developed to characterize intermediates during a chemical reaction-thus revealing mechanistic steps that are unobservable without fluorescence lifetime data. These findings impact organometallic reagent synthesis and catalysis by providing a previously uncharacterized mechanistic role for a widely used activating agent, an understanding of which is suitable for revising activation models and for developing strategies to activate currently unreactive metals.
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Affiliation(s)
- Erin M Hanada
- Chemistry Department, University of California, Irvine, Irvine, CA 92697-2025, USA
| | - Patrick J McShea
- Chemistry Department, University of California, Irvine, Irvine, CA 92697-2025, USA
| | - Suzanne A Blum
- Chemistry Department, University of California, Irvine, Irvine, CA 92697-2025, USA
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Terlecki M, Justyniak I, Leszczyński MK, Bernatowicz P, Lewiński J. Factors controlling the structure of alkylzinc amidinates: on the role of N-substituents. Dalton Trans 2023; 52:2712-2721. [PMID: 36748844 DOI: 10.1039/d2dt03722j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Despite various applications of alkylzinc complexes supported by N,N-bidentate ligands in chemistry and materials science, the corresponding organozinc amidinates still represent an insufficiently explored area. To gain a more in-depth understanding of factors controlling the structure and stability of alkylzinc amidinates, we selected benzamidinate and N,N'-diphenylformamidinate ligands as model N,N'-unsubstituted and N,N'-diaryl substituted ligands, respectively, to systematically modify the secondary coordination sphere of the Zn center. A series of new alkylzinc amidinates has been synthesized and their molecular structures identified in both the solid state (single-crystal X-ray crystallography) and solution (NMR and FTIR spectroscopy). The results indicate that [RZnL]x-type amidinate moieties are essentially unstable and tend to undergo Schlenk equilibria-mediated ligand scrambling leading to more thermodynamically stable non-stoichiometric [R2Zn3L4]- and [R3Zn4L5]-type complexes. This process is significantly influenced by the secondary coordination sphere noncovalent interactions as well as the steric hindrance provided by both zinc-bounded alkyl groups and the N-substituents.
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Affiliation(s)
- Michał Terlecki
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland.
| | - Iwona Justyniak
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Michał K Leszczyński
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland. .,Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Piotr Bernatowicz
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Janusz Lewiński
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland. .,Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
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Hanada EM, Tagawa TKS, Kawada M, Blum SA. Reactivity Differences of Rieke Zinc Arise Primarily from Salts in the Supernatant, Not in the Solids. J Am Chem Soc 2022; 144:12081-12091. [PMID: 35767838 PMCID: PMC9970556 DOI: 10.1021/jacs.2c02471] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Contrary to prevailing thought, the salt content of supernatants is found to dictate reactivity differences of different preparation methods of Rieke zinc toward oxidative addition of organohalides. This conclusion is established through combined single-particle microscopy and ensemble spectroscopy experiments, coupled with careful removal or keeping of the supernatants during Rieke zinc preparations. Fluorescence microscopy experiments with single-Rieke-zinc-particle resolution determined the microscale surface reactivity of the Rieke zinc in the absence of supernatants, thus pinpointing its inherent reactivity independent of the convoluting supernatant composition. In parallel experiments, scanning electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma-mass spectrometry characterized the zinc metal chemical composition at the bulk and single-particle levels. Proton nuclear magnetic resonance spectroscopy kinetics characterized bench-scale Rieke zinc reactivity in the presence and absence of different supernatants and exogenous salt additives. Together, these experiments show that the differences in reactivity from sodium-reduced vs lithium-reduced Rieke zinc arise from the residual salts in the supernatant rather than the differing salt compositions of the solids. This supernatant salt also determines the structure of the ultimate organozinc product, generating either the diorganozinc or monoorganozinc halide complex. That different organozinc complexes formed upon direct insertion to different preparations of Rieke zinc was not previously reported, despite Rieke zinc's widespread use. These findings impact organozinc-reagent and nanomaterial synthesis by showing that, unexpectedly, desired Rieke zinc reactivity can be achieved through simple addition of soluble salts to solutions that were used to prepare the metals─a substantially easier synthetic manipulation than solid composition and morphology control.
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Affiliation(s)
- Erin M. Hanada
- Chemistry Department, University of California, Irvine, Irvine, California 92697-2025, United States
| | | | - Masamu Kawada
- Chemistry Department, University of California, Irvine, Irvine, California 92697-2025, United States
| | - Suzanne A. Blum
- Chemistry Department, University of California, Irvine, Irvine, California 92697-2025, United States
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Charboneau DJ, Hazari N, Huang H, Uehling MR, Zultanski SL. Homogeneous Organic Electron Donors in Nickel-Catalyzed Reductive Transformations. J Org Chem 2022; 87:7589-7609. [PMID: 35671350 PMCID: PMC9335070 DOI: 10.1021/acs.joc.2c00462] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Many contemporary organic transformations, such as Ni-catalyzed cross-electrophile coupling (XEC), require a reductant. Typically, heterogeneous reductants, such as Zn0 or Mn0, are used as the electron source in these reactions. Although heterogeneous reductants are highly practical for preparative-scale batch reactions, they can lead to complications in performing reactions on process scale and are not easily compatible with modern applications, such as flow chemistry. In principle, homogeneous organic reductants can address some of the challenges associated with heterogeneous reductants and also provide greater control of the reductant strength, which can lead to new reactivity. Nevertheless, homogeneous organic reductants have rarely been used in XEC. In this Perspective, we summarize recent progress in the use of homogeneous organic electron donors in Ni-catalyzed XEC and related reactions, discuss potential synthetic and mechanistic benefits, describe the limitations that inhibit their implementation, and outline challenges that need to be solved in order for homogeneous organic reductants to be widely utilized in synthetic chemistry. Although our focus is on XEC, our discussion of the strengths and weaknesses of different methods for introducing electrons is general to other reductive transformations.
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Affiliation(s)
- David J Charboneau
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Nilay Hazari
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Haotian Huang
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Mycah R Uehling
- Discovery Chemistry, HTE and Lead Discovery Capabilities, Merck & Co., Inc., Kenilworth, New Jersey 07033, United States
| | - Susan L Zultanski
- Department of Process Research and Development, Merck & Co., Inc., Kenilworth, New Jersey 07033, United States
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Peacock H, Blum SA. Single-Micelle and Single-Zinc-Particle Imaging Provides Insights into the Physical Processes Underpinning Organozinc Reactions in Water. J Am Chem Soc 2022; 144:3285-3296. [PMID: 35156815 DOI: 10.1021/jacs.2c00421] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Micelles on the surfaces of individual metallic zinc particles are imaged by fluorescence microscopy with sensitivity up to single micelles. These micelles are made fluorescent to enable imaging, through the incorporation of boron dipyrromethene fluorophores as representative organic molecular "cargo". Highlighting an advantage of this in situ and sensitive fluorescence technique, the same micelles are not visible by ex situ scanning electron microscopy/energy dispersive X-ray spectroscopy analysis. Examination of micellar solutions with zinc reveals an aging process: micelles do not immediately adhere to the zinc surfaces upon mixing but rather build up over time. Furthermore, at longer times, smaller zinc particles become fully encased in micelle "shells". Once adhered, micelles remain in the local regions of the zinc surface for the duration of the imaging experiments (>2 h). Single micelles are imaged in solution, and their molecular contents are characterized. Two-color fluorescence crossover experiments show that micelles adhered to the surface of the zinc exchange molecular contents with micelles in solution, achieving molecular exchange equilibrium in ∼2.5 h. Unique (non-ensemble averaged) exchange kinetics are displayed by micelles at different locations on the zinc surface, consistent with exchange kinetics of single micelles or small local clusters of micelles. The aging of the micellar solutions and the rate of exchange while on the surface of the zinc suggest that micelle mass transport processes may contribute to overall reaction barriers in sustainable organozinc cross-coupling reactions in micellar water. The observed aging of the system suggests routes for improvement of preparative, bench-scale synthetic reactions involving micellar preparations of organozinc compounds.
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Affiliation(s)
- Hannah Peacock
- Department of Chemistry, University of California, Irvine, Irvine, California 92697-2025, United States
| | - Suzanne A Blum
- Department of Chemistry, University of California, Irvine, Irvine, California 92697-2025, United States
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Saini A, Messenger H, Kisley L. Fluorophores "Turned-On" by Corrosion Reactions Can Be Detected at the Single-Molecule Level. ACS APPLIED MATERIALS & INTERFACES 2021; 13:2000-2006. [PMID: 33356107 DOI: 10.1021/acsami.0c18994] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
We demonstrate that fluorogenic molecules that "turn-on" upon redox reactions can sense the corrosion of iron at the single-molecule scale. We first observe the cathodic reduction of nonfluorescent resazurin to fluorescent resorufin in the presence of iron in bulk solution. The progression of corrosion is seen as a color change that is quantified as an increase in fluorescence emission intensity. We show that the fluorescence signal is directly related to the amount of electrons that are available due to corrosion progression and can be used to quantify the catalyzed increase in the rate of corrosion by NaCl. By using modern fluorescence microscopy instrumentation we detect real-time, single-molecule "turn-on" of resazurin by corrosion, overcoming the previous limitations of microscopic fluorescence corrosion detection. Analysis of the total number of individual resorufin molecules shows heterogeneities during the progression of corrosion that are not observed in ensemble measurements. Finally, we discuss the potential for single-molecule kinetic and super-resolution localization analysis of corrosion based on our findings. Single-molecule florescence microscopy opens up a new spatiotemporal regime to study corrosion at the molecular level.
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Affiliation(s)
- Anuj Saini
- Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - Hannah Messenger
- Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - Lydia Kisley
- Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106, United States
- Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106, United States
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