General cross-coupling reactions with adaptive dynamic homogeneous catalysis

Ghosh I., Shlapakov N., Karl T.A., Düker J., Nikitin M., Burykina J.V., Ananikov V.P. and König B., Nature, 2023.
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Cross-coupling reactions are among the most important transformations in modern organic synthesis. Although the range of reported (het)aryl halides and nucleophile coupling partners is very large considering various protocols, the reaction conditions vary considerably between compound classes, necessitating renewed case-by-case optimization of the reaction conditions. Here we introduce adaptive dynamic homogeneous catalysis (AD-HoC) with nickel under visible-light-driven redox reaction conditions for general C(sp2)–(hetero)atom coupling reactions. The self-adjustive nature of the catalytic system allowed the simple classification of dozens of various classes of nucleophiles in cross-coupling reactions. This is synthetically demonstrated in nine different bond-forming reactions (in this case, C(sp2)–S, Se, N, P, B, O, C(sp3, sp2, sp), Si, Cl) with hundreds of synthetic examples under predictable reaction conditions. The catalytic reaction centre(s) and conditions differ from one another by the added nucleophile, or if required, a commercially available inexpensive amine base.

Time-Resolved Formation and Operation Maps of Pd Catalysts Suggest a Key Role of Single Atom Centers in Cross-Coupling

Galushko A.S., Boiko D.A., Pentsak E.O., Eremin D.B., Ananikov V.P., J. Am. Chem. Soc., 2023, ASAP.
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An approach to the spatially localized characterization of supported catalysts over a reaction course is proposed. It consists of a combination of scanning, transmission, and high-resolution scanning transmission electron microscopy to determine metal particles from arrays of surface nanoparticles to individual nanoparticles and individual atoms. The study of the evolution of specific metal catalyst particles at different scale levels over time, particularly before and after the cross-coupling catalytic reaction, made it possible to approach the concept of 4D catalysis–tracking the positions of catalytic centers in space (3D) over time (+1D). The dynamic behavior of individual palladium atoms and nanoparticles in cross-coupling reactions was recorded with nanometer accuracy via the precise localization of catalytic centers. Single atoms of palladium leach out into solution from the support under the action of the catalytic system, where they exhibit extremely high catalytic activity compared to surface metal nanoparticles. Monoatomic centers, which make up only approximately 1% of palladium in the Pd/C system, provide more than 99% of the catalytic activity. The remaining palladium nanoparticles changed their shape and could move over the surface of the support, which was recorded by processing images of the array of nanoparticles with a neural network and aligning them using automatically detected keypoints. The study reveals a novel opportunity for single-atom catalysis─easier detachment (capture) from (on) the carbon support surface is the origin of superior catalytic activity, rather than the operation of single atomic catalytic centers on the surface of the support, as is typically assumed.

Transition-Metal-Catalyzed C–S, C–Se, and C–Te Bond Formations via Cross-Coupling and Atom-Economic Addition Reactions. Achievements and Challenges

Beletskaya I.P., Ananikov V. P., Chem. Rev., 2022, 122, 16110–16293.
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In the present review, we discuss recent progress in the field of C–Z bond formation reactions (Z = S, Se, Te) catalyzed by transition metals. Two complementary methodologies are considered─catalytic cross-coupling reactions and catalytic addition reactions. The development of advanced catalytic systems is aimed at improved catalyst efficiency, reduced catalyst loading, better cost efficiency, environmental concerns, and higher selectivity and yields. The important rise of research efforts in sustainability and green chemistry areas is critically assessed. The paramount role of mechanistic studies in the development of a new generation of catalytic systems is addressed, and the key achievements, problems, and challenges are summarized for this field.

Fully Automated Unconstrained Analysis of High-Resolution Mass Spectrometry Data with Machine Learning

Boiko D.A., Kozlov K.S., Burykina Yu.V., Ilyushenkova V.V., Ananikov V.P. , J. Am. Chem. Soc., 2022, 144, 14590-14606.
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Mass spectrometry (MS) is a convenient, highly sensitive, and reliable method for the analysis of complex mixtures, which is vital for materials science, life sciences fields such as metabolomics and proteomics, and mechanistic research in chemistry. Although it is one of the most powerful methods for individual compound detection, complete signal assignment in complex mixtures is still a great challenge. The unconstrained formula-generating algorithm, covering the entire spectra and revealing components, is a "dream tool" for researchers. We present the framework for efficient MS data interpretation, describing a novel approach for detailed analysis based on deisotoping performed by gradient-boosted decision trees and a neural network that generates molecular formulas from the fine isotopic structure, approaching the long-standing inverse spectral problem. The methods were successfully tested on three examples: fragment ion analysis in protein sequencing for proteomics, analysis of the natural samples for life sciences, and study of the cross-coupling catalytic system for chemistry.

Toward Totally Defined Nanocatalysis: Deep Learning Reveals the Extraordinary Activity of Single Pd/C Particles

Eremin D.B., Galushko A.S., Boiko D.A., Pentsak E.O., Chistyakov I.V., Ananikov V. P., J. Am. Chem. Soc., 2022, 144, 6071–6079.
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Homogeneous catalysis is typically considered "well-defined" from the standpoint of catalyst structure unambiguity. In contrast, heterogeneous nanocatalysis often falls into the realm of "poorly defined" systems. Supported catalysts are difficult to characterize due to their heterogeneity, variety of morphologies, and large size at the nanoscale. Furthermore, an assortment of active metal nanoparticles examined on the support are negligible compared to those in the bulk catalyst used. To solve these challenges, we studied individual particles of the supported catalyst. We made a significant step forward to fully characterize individual catalyst particles. Combining a nanomanipulation technique inside a field-emission scanning electron microscope with neural network analysis of selected individual particles unexpectedly revealed important aspects of activity for widespread and commercially important Pd/C catalysts. The proposed approach unleashed an unprecedented turnover number of 10 9 attributed to individual palladium on a nanoglobular carbon particle. Offered in the present study is the Totally Defined Catalysis concept that has tremendous potential for the mechanistic research and development of high-performance catalysts.

Intermolecular Photocatalytic Chemo-, Stereo- and Regioselective Thiol-yne-ene Coupling Reaction

Burykina Ju.V., Kobelev A.D., Shlapakov N.S., Kostyukovich A.Yu., Fakhrutdinov A.N., König B., Ananikov V.P., Angew. Chem. Int. Ed., 2022, 61, e202116888.
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The first example of an intermolecular thiol-yne-ene coupling reaction is reported for the one-pot construction of C-S and C-C bonds. This opens a new dimension in building molecular complexity to access densely functionalized products. The progress was achieved by suppressing hydrogen atom transfer (HAT) and associative reductant upconversion (via associative electron upconversion C-S three-electron σ-bond formation) using an Eosin Y/DBU/MeOH photocatalytic system. Investigation of the reaction mechanism by combining online ESI-UHRMS, EPR spectroscopy, isotope labeling, determination of quantum yield and computational modeling revealed a unique photoredox cycle with four radical-involving stages. Previously unavailable products of the thiol-yne-ene reaction were obtained in good yields with high selectivity and can serve as stable precursors for the synthesis of synthetically demanding activated 1,3-dienes.

One-Step Access to Heteroatom-Functionalized Imidazol(in)ium Salts

Pasyukov D.V., Shevchenko M.A., Shepelenko K.E., Khazipov O.V., Burykina J.V., Gordeev E.G., Minyaev M.E., Chernyshev V.M. and Ananikov V.P., Angew. Chem. Int. Ed., 2022, 61, e202116131.
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Imidazolium salts have ubiquitous applications in energy research, catalysis, materials and medicinal sciences. Here, we report a new strategy for the synthesis of diverse heteroatom-functionalized imidazolium and imidazolinium salts from easily available 1,4-diaza-1,3-butadienes in one step. The strategy relies on a discovered family of unprecedented nucleophilic addition/cyclization reactions with trialkyl orthoformates and heteroatomic nucleophiles. To probe general areas of application, synthesized N-heterocyclic carbene (NHC) precursors were feasible for direct metallation to give functionalized M/carbene complexes (M = Pd, Ni, Cu, Ag, Au), which were isolated in individual form. The utility of chloromethyl function for the postmodification of the synthesized salts and Pd/carbene complexes was demonstrated. The obtained complexes and imidazolium salts demonstrated good activities in Pd- or Ni-catalyzed model cross-coupling and C-H activation reactions.

Nickel and Palladium Catalysis: Stronger Demand than Ever

Chernyshev V.M., Ananikov V.P., ACS Catal., 2022, 12, 1180-1200.
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Key similarities and differences of Pd and Ni in catalytic systems are discussed. Overall, Ni and Pd catalyze a vast number of similar C–C and C–heteroatom bond-forming reactions. However, the smaller atomic radius and lower electronegativity of Ni, as well as the more negative redox potentials of low-valent Ni species, often provide higher reactivity of Ni systems in oxidative addition or insertion reactions and higher persistence of alkyl-Ni intermediates against β-hydrogen elimination, thus enabling activation of more reluctant electrophiles, including alkyl electrophiles. Another key point relates to the higher stability of the open-shell electronic configurations of Ni(I) and Ni(III) compared with Pd(I) and Pd(III). Nickel systems very often involve a number of interconvertible Ni( n+) active species of variable oxidation states (Ni(0), Ni(I), Ni(II), and Ni(III)). In contrast, catalytic reactions involving Pd(I) or Pd(III) active species are still relatively less developed and may require facilitation by special ligands or merging with photo- or electrocatalysis. However, the relatively high redox potentials of Pd(n+) species ensure their facile reduction to Pd(0) species under the assistance of numerous reagents or solvents, providing relatively high concentrations of molecular Pd1(0) complexes that can reversibly aggregate into active Pdn clusters and nanoparticles to form a cocktail of interconvertible Pdn(0) active species of various nuclearities (i.e., various values of "n"). Nickel systems involving Ni(0) complexes often require special strong reductants; they are more sensitive to deactivation by air and other oxidizers and, as consequence, often operate at higher catalyst loadings than palladium systems in the same reactions. The ease of activation and relatively high stability of low-valent active Pd species provide high robustness and versatility for palladium catalysis, whereas a variety of Ni oxidation states enables more diverse and uncommon reactivity, albeit requiring higher efforts in the activation and stabilization of nickel catalytic systems. As a point for discussion, we may note that Pd catalytic systems may easily form a "cocktail of particles" of different nuclearities but similar oxidation states (Pd1, Pdn, Pd NPs), whereas nickel may behave as a "cocktail of species" in different oxidation states but is less variable in stable nuclearities. Undoubtedly, there is stronger demand than ever not only to develop improved efficient catalysts but also to understand the mechanisms of Pd and Ni catalytic systems.

“Hidden” Nanoscale Catalysis in Alkyne Hydrogenation with Well-Defined Molecular Pd/NHC Complexes

Denisova E.A., Kostyukovich A. Yu., Fakhrutdinov A. N., Korabelnikova V. A., Galushko A.S., and Ananikov V.P., ACS Catal., 2022, 12, 6980–6996.
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Pd/NHC complexes are widely used as catalysts in hydrogenation reactions. Usually, the operating mode of these systems is referred to as homogeneous. In this work, we demonstrated that mixed homogeneous–heterogeneous catalysis can be realized in the hydrogenation reaction when Pd/NHC complexes were used as precatalysts. Palladium NPs are formed in situ and act as "hidden" nanoscale catalysts. Based on the quantum chemical calculations and experimental XPS results, the presence of surface NHC ligands on metal nanoparticles can be proposed. Herein, we propose a method for the determination of dynamic transformations of Pd/NHC complexes in transfer hydrogenation reactions via 13C labeling and NMR spectroscopy. This approach is based on the introduction of a 13C label in the C2 position of the imidazolium fragment of Pd/NHC, which is unique to the M–NHC bond. It was found using NMR, ESI-MS, and TEM monitoring of the transfer semihydrogenation of diphenylacetylene that Pd/NHC complexes disappear from the reaction mixtures at the early stage of reaction. Palladium atoms pass into a heterogeneous phase, forming NPs with sizes ranging from 1 to 9 nm. The experimental study and calculations performed in the present study revealed the role of the ligands on the surface of metal nanoparticles. Comparative modeling of hydrogenation reactions on ligand-free and NHC-modified Pd clusters showed that modification of the metal surface increased the catalytic activity by reducing the potential barriers of the alkyne syn-addition and reductive elimination stages. Since the presence of an NHC ligand in the catalytic system leads to a change in the rate-limiting stage of the reaction, we proposed a combined reaction mechanism, according to which oxidative addition proceeds on a bare metal surface, and the remaining two stages occur in the modified zone of NPs.

The dawn of cross-coupling

Ananikov V. P., Nature Catalysis, 2021, 9, 3011-3042.
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Methods for the direct one-step replacement of a hydrogen atom in a C–H bond by an organic functional group can create enormous possibilities for synthetic applications. On the way to solve this challenge, the discovery of the reaction of organopalladium complexes with olefins opened a new era in catalysis and organic chemistry.

Visualization of the Mechanical Wave Effect on Liquid Microphases and Its Application for the Tuning of Dissipative Soft Microreactors

Kashin A. S., Degtyareva E. S., Ananikov V. P., J. Am. Chem. Soc. Au, 2021, ASAP.
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The development of approaches for creation of adaptive and stimuli-responsive chemical systems is particularly important for chemistry, materials science, and biotechnology. The understanding of response mechanisms for various external forces is highly demanded for the rational design of task-specific systems. Here, we report direct liquid-phase scanning electron microscopy (SEM) observations of the high frequency sound-wave-driven restructuring of liquid media on the microlevel, leading to switching of its chemical behavior. We show that under the action of ultrasound, the microstructured ionic liquid/water mixture undergoes rearrangement resulting in formation of separated phases with specific compositions and reactivities. The observed effect was successfully utilized for creation of dissipative soft microreactors formed in ionic liquid/water media during the sonication-driven water transfer. The performance of the microreactors was demonstrated using the example of controlled synthesis of small and uniform gold and palladium nanoparticles. The microsonication stage, designed and used in the present study, opened unique opportunities for direct sonochemical studies with the use of electron microscopy.

Development of 3D+G Printing for the Design of Customizable Flow Reactors

Kucherov F.A., Romashov L.V., Ananikov V.P., Chem. Engin. J., 2021, 132670.
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An in-depth study of chemical processes at plastic-metal interfaces led to the development of a novel approach to the creation of lab-on-a-chip microflow reactors. The developed method combines 3D printing of the reactor core by fused deposition modeling using conventional plastic material (ABS), followed by chemical (electroless copper) and galvanic plating (nickel) of the resulting piece (in overall, 3D+G printing process). Detailed analysis of the pieces along all 3D+G stages by electron microscopy revealed step-by-step processes on the plastic-metal interface, which finally allowed innovative reactor design. Despite being made from low-cost materials in a simple procedure, flow reactors are characterized by chemical resistance, versatile geometry, modular design and excellent operating performance. Complete reactor assembly was formulated and successfully tested in a variety of chemical processes targeted on biologically active molecules, including homogeneous, heterogeneous and photochemical reactions. Reactor modules can be combined into cascades to perform sequential reactions. Metallized reactors can be used multiple times in a variety of chemical processes.

Carbocatalytic Acetylene Cyclotrimerization: A Key Role of Unpaired Electron Delocalization

Gordeev E.G., Pentsak E.O., Ananikov V.P., J. Am. Chem. Soc., 2020, 142, 3784-3796.
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Development of sustainable catalysts for synthetic transformations is one of the most challenging and demanding goals. The high prices of precious metals and the unavoidable leaching of toxic metal species leading to environmental contamination make the transition metal-free catalytic systems especially important. Here we demonstrate that carbene active centers localized on carbon atoms at the zigzag edge of graphene represent an alternative platform for efficient catalytic carbon–carbon bond formation in the synthesis of benzene. The studied acetylene trimerization reaction is an efficient atom-economic route to build an aromatic ring—a step ubiquitously important in organic synthesis and industrial applications. Computational modeling of the reaction mechanism reveals a principal role of the reversible spin density oscillations that govern the overall catalytic cycle, facilitate the product formation, and regenerate the catalytically active centers. Dynamic π-electron interactions in 2D carbon systems open new opportunities in the field of carbocatalysis, unachievable by means of transition metal-catalyzed transformations. The theoretical findings are confirmed experimentally by generating key moieties of the carbon catalyst and performing the acetylene conversion to benzene.

Introducing tox‐Profiles of Chemical Reactions

Egorova K.S., Galushko A.S., Ananikov V.P., Angew. Chem. Int. Ed., 2020, 59, 22296-22305.
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In this Essay, we present a critical analysis of two common practices in modern chemistry—that is, of using speculations about the "greenness" and "nontoxicity" of developed synthesis procedures and of a priori labelling various compounds derived from natural sources as being environmentally safe. We note that every organic molecule that contains functional groups should be biologically active. Thus, analysis of the particular greenness and the potential environmental impact of a given chemical process should account for the biological activity of all its components in a measureable (rather than empirical) way. We highlight the necessity of clarifying discussions on biological activity and toxicity and propose possible ways of introducing tox‐Profiles as a reliable overview of the overall toxicity of chemical reactions.

Pd-Catalyzed Synthesis of Densely Functionalized Cyclopropyl Vinyl Sulfides Reveals the Origin of High Selectivity in a Fundamental Alkyne Insertion Step

Sahharova L.T., Gordeev E.G., Eremin D.B., Ananikov V.P., ACS Catal., 2020, 10, 9872–9888.
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Catalytic atom-economic hydrothiolation of cyclopropyl acetylenes was developed. Using Pd/NHC complex as a precatalyst, regioselective addition of thiols to cyclopropyl acetylenes was successfully performed, leading to densely functionalized compounds in excellent selectivity (up to 99:1) and high yields (up to 99%). Formation of Markovnikov-type products by insertion of alkyne into the Pd–S bond was confirmed experimentally. Molecular dynamics of the alkyne insertion into the Pd–S bond was performed computationally to identify key factors controlling the remarkable regioselectivity of this process. The fundamental question of how a small difference in activation energies can result in very high regioselectivity has been addressed by experimental methods combined with computational modeling. We show that the insertion of alkyne into the Pd–S bond proceeds by an asynchronous mechanism, which starts with metal–carbon binding and resolves into diverse transient structures. We further demonstrate that dynamic involvement of these structures ensures regioselectivity of the entire process, thus providing a mechanistic link that has long been missing. Alkyne insertion into the metal–heteroatom bond is a fundamental elementary step and a corner stone of catalysis and organometallic chemistry that works for a large variety of metals and heteroatoms. Mastering its Markovnikov vs anti-Markovnikov selectivity provides powerful opportunities for the design of selective functionalization routes.

Directing-Group-Free, Carbonyl Group-Promoted Catalytic C–H Arylation of Bio-Based Furans

Karlinskii B.Ya., Kostyukovich A.Yu., Kucherov F.A., Galkin K.I., Kozlov K.S., Ananikov V.P., ACS Catal., 2020, 10, 11466–11480.
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An efficient strategy was developed for directing-group-free C–H functionalization of biomass-derived C6 furanic building block. Palladium-catalyzed C–H functionalization of the low-reactive C3 position was successfully performed in 2,5-diformylfuran, an important derivative of the biobased platform chemical 5-(hydroxymethyl)furfural. The ligand-free catalytic arylation was carried out without using protecting or directing groups, which is of key importance for the studied area to achieve waste-minimized and step-economic biomass processing. The experimental results combined with density functional theory calculations revealed a reaction mechanism and indicated that the presence of the aldehyde group is essential for catalytic reaction. Enolization of the aldehyde group and Pd binding play an important role in governing the overall C–H functionalization pathway. One of the obtained arylated furanic compounds was tested as a model substrate for reduction and oxidation of carbonyl groups to highlight its versatile synthetic potential.

The Key Role of R-NHC Couplings (R = C, H, Heteroatom) and M-NHC Bond Cleavage in the Evolution of M/NHC Complexes and Formation of Catalytically Active Species

Chernyshev V. M., Denisova E.A., Eremin D. B., Ananikov V. P., Chem. Sci., 2020, 11, 6957-6977.
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Complexes of metals with N-heterocyclic carbene ligands (M/NHC) are typically considered the systems of choice in homogeneous catalysis due to their stable metal−ligand framework. However, it becomes obvious that even metal species with a strong M-NHC bond can undergo evolution in catalytic systems, and processes of M-NHC bond cleavage are common for different metals and NHC ligands. This review is focused on the main types of the M-NHC bond cleavage reactions and their impact on activity and stability of M/NHC catalytic systems. For the first time, we consider these processes in terms of NHC-connected and NHC-disconnected active species derived from M/NHC precatalysts and classify them as fundamentally different types of catalysts. Problems of rational catalyst design and sustainability issues are discussed in the context of the two different types of M/NHC catalysis mechanisms.

Selectivity Control in Thiol-yne Click Reactions via Visible Light Induced Associative Electron Upconversion

Burykina J.V., Shlapakov N.S., Gordeev E.G., König B., Ananikov V.P., Chem. Sci., 2020, 11, 10061-10070.
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An associative electron upconversion is proposed as a key step determining the selectivity of the thiol-yne coupling. The developed synthetic approach provided an efficient tool to access a comprehensive range of products - four types of vinyl sulfides were prepared in high yields and selectivity. Practically important, here we report the transition-metal-free regioselective thiol-yne addition and formation of the demanding Markovnikov-type product by radical photoredox reaction. The photochemical process was directly monitored by mass-spectrometry in a specially designed ESI-MS device with green laser excitation in the spray chamber. The proposed reaction mechanism is supported by experiments and DFT calculations.

Monitoring Chemical Reactions in Liquid Media Using Electron Microscopy

Kashin A. S., Ananikov V. P., Nat. Rev. Chem., 2019, 3, 624–637.
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Developments in chemistry, materials science and biology have been fuelled by our search for structure–property relationships in matter at different levels of organization. Transformations in chemical synthesis and living systems predominantly take place in solution, such that many efforts have focused on studying nanoscale systems in the liquid phase. These studies have largely relied on spectroscopic data, the assignment of which can often be ambiguous. By contrast, electron microscopy can be used to directly visualize chemical systems and processes with up to atomic resolution. Electron microscopy is most amenable to studying solid samples and, until recently, to study a liquid phase, one had to remove solvent and lose important structural information. Over the past decade, however, liquid-phase electron microscopy has revolutionized direct mechanistic studies of reactions in liquid media. Scanning electron microscopy and (scanning) transmission electron microscopy of liquid samples have enabled breakthroughs in nanoparticle chemistry, soft-matter science, catalysis, electrochemistry, battery research and biochemistry. In this Review, we discuss the utility of liquid-phase electron microscopy for studying chemical reaction mechanisms in liquid systems.

Phantom Reactivity in Organic and Catalytic Reactions as a Consequence of Microscale Destruction and Contamination-Trapping Effects of Magnetic Stir Bars

Pentsak E.O., Eremin D.B., Gordeev E.G., Ananikov V.P., ACS Catal., 2019, 9, 3070-3081.
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Magnetic stir bars are routinely used by every chemist doing synthetic or catalytic transformations in solution. Each bar lasts for months or years, as the regular PTFE (polytetrafluoroethylene) coating is believed to be highly durable, inert, and resistant to multiple washings and cleanings. By using electron microscopy, we found out quite unexpectedly that the surface of magnetic stir bars is susceptible to microscale destruction and forms various types of defects. These microscopic defects effectively trap and accumulate trace amounts of active components from reaction mixtures, most notably metal species. Trapped in surface defects, the impurities escape elimination by washing and cleaning, thus remaining on the surface. FE-SEM/EDX analysis shows that the surface of used stir bars is littered with contaminants representing a variety of metals (Pd, Pt, Au, Fe, Co, Cr, etc.). ESI-MS monitoring corroborates the transfer of the trace metal species to reaction mixtures, while chemical tests indicate their significant catalytic activity. A theoretical DFT study reveals a remarkably high binding energy of metal atoms to the PTFE surface, especially in cases of local mechanical disruption or chemical influence. A plausible mechanism of PTFE surface contamination is suggested, and the results show that metal contamination of reusable polymer-coated labware is greatly underestimated. The present study suggests that corresponding control experiments with an unused stir bar (to avoid misinterpretations due to the influence of contamination of magnetic stir bars) are a "must do" for reporting high-performance catalytic reactions, reactions with low catalyst loadings, metal-catalyst-free reactions, and mechanistic studies.

Pd and Pt Catalyst Poisoning in the Study of Reaction Mechanisms: What Does the Mercury Test Mean for Catalysis?

Chernyshev V.M., Astakhov A.V., Chikunov I.E., Tyurin R.V., Eremin D.B., Ranny G.S., Khrustalev V.N., Ananikov V.P., ACS Catal., 2019, 9, 2984-2995.
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The mercury test is a rapid and widely used method for distinguishing truly homogeneous molecular catalysis from nanoparticle metal catalysis. In the current work, using various M 0 and MII complexes of palladium and platinum that are often used in homogeneous catalysis as examples, we demonstrated that the mercury test is generally inadequate as a method for distinguishing between homogeneous and cluster/nanoparticle catalysis mechanisms for the following reasons: (i) the general and facile reactivity of both molecular M0 and MII complexes toward metallic mercury and (ii) the very high and often unpredictable dependence of the test results on the operational conditions and the inability to develop universal quantitatively defined operational parameters. Two main types or mercury-induced transformations, the cleavage of M0 complexes and the oxidative–reductive transmetalation of MII complexes, including a reaction of highly popular MII/NHC complexes, were elucidated using NMR, ESI-MS, and EDXRF techniques. A mechanistic picture of the reactions involving metal complexes was revealed with mercury, and representative metal species were isolated and characterized. Even in an attempt to not overstate the results, one must note that the use of the mercury tests often leads to inaccurate conclusions and complicates the mechanistic studies of these catalytic systems. As a general concept, distinguishing reaction mechanisms (homogeneous vs cluster/nanoparticle) by using catalyst poisoning requires careful rethinking in the case of dynamic catalytic systems.

Exploring the performance of nanostructured reagents with organic-group-defined morphology in cross-coupling reaction

Kashin A. S., Degtyareva E. S., Eremin D. B., Ananikov V. P., Nat. Commun., 2018, 9, 2936.
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The great impact of the nanoscale organization of reactive species on their performance in chemical transformations creates the possibility of fine-tuning of reaction parameters by modulating the nano-level properties. This methodology is extensively applied for the catalysts development whereas nanostructured reactants represent the practically unexplored area. Here we report the palladium- and copper-catalyzed cross-coupling reaction involving nano-structured nickel thiolate particles as reagents. On the basis of experimental findings we propose the cooperative effect of nano-level and molecular-level properties on their reactivity. The high degree of ordering, small particles size, and electron donating properties of the substituents favor the product formation. Reactant particles evolution in the reaction is visualized directly by dynamic liquid-phase electron microscopy including recording of video movies. Mechanism of the reaction in liquid phase is established using on-line mass spectrometry measurements. Together the findings provide new opportunities for organic chemical transformations design and for mechanistic studies.

Revealing the Unusual Role of Bases in Activation/Deactivation of Catalytic Systems: O–NHC Coupling in M/NHC Catalysis

Chernyshev V. M., Khazipov O. V., Shevchenko M. A., Chernenko A. Yu., Astakhov A. V., Eremin D. B., Pasyukov D. V., Kashin A. S., Ananikov V. P., Chem. Sci., 2018, 9, 5564-5577.
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Numerous reactions are catalyzed by complexes of metals (M) with N-heterocyclic carbene (NHC) ligands, typically in the presence of oxygen bases, which significantly shape the performance. It is generally accepted that bases are required for either substrate activation (exemplified by transmetallation in the Suzuki cross-coupling), or HX capture (e.g. in a variety of C–C and C-heteroatom couplings, the Heck reaction, C–H functionalization, heterocyclizations, etc.). This study gives insights into the behavior of M(II)/NHC (M = Pd, Pt, Ni) complexes in solution under the action of bases conventionally engaged in catalysis (KOH, NaOH, t-BuOK, Cs2CO3, K2CO3, etc.). A previously unaddressed transformation of M(II)/NHC complexes under conditions of typical base-mediated M/NHC catalyzed reactions is disclosed. Pd(II) and Pt(II) complexes widely used in catalysis react with the bases to give M(0) species and 2(5)-oxo-substituted azoles via an O–NHC coupling mechanism. Ni(NHC)2X2 complexes hydrolyze in the presence of aqueous potassium hydroxide, and undergo the same O–NHC coupling to give azolones and metallic nickel under the action of t-BuOK under anhydrous conditions. The study reveals a new role of NHC ligands as intramolecular reducing agents for the transformation of M(II) into "ligandless" M(0) species. This demonstrates that the disclosed base-mediated O–NHC coupling reaction is integrated into the catalytic M/NHC systems and can define the mechanism of catalysis (molecular M/NHC vs. "NHC-free" cocktail-type catalysis). A proposed mechanism of the revealed transformation includes NHC-OR reductive elimination, as implied by a series of mechanistic studies including 18O labeling experiments.

“Solvent-in-Salt” Systems for Design of New Materials in Chemistry, Biology and Energy Research

Azov V. A., Egorova K. S., Seitkalieva M. M., Kashin A. S., Ananikov V. P., Chem. Soc. Rev., 2018, 47, 1250-1284 .
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Inorganic and organic "solvent-in-salt" (SIS) systems have been known for decades but have attracted significant attention only recently. Molten salt hydrates/solvates have been successfully employed as non-flammable, benign electrolytes in rechargeable lithium-ion batteries leading to a revolution in battery development and design. SIS with organic components (for example, ionic liquids containing small amounts of water) demonstrate remarkable thermal stability and tunability, and present a class of admittedly safer electrolytes, in comparison with traditional organic solvents. Water molecules tend to form nano- and microstructures (droplets and channel networks) in ionic media impacting their heterogeneity. Such microscale domains can be employed as microreactors for chemical and enzymatic synthesis. In this review, we address known SIS systems and discuss their composition, structure, properties and dynamics. Special attention is paid to the current and potential applications of inorganic and organic SIS systems in energy research, chemistry and biochemistry. A separate section of this review is dedicated to experimental methods of SIS investigation, which is crucial for the development of this field.

3D Printing with Biobased PEF for Carbon Neutral Manufacturing

Kucherov F.A., Gordeev E.G., Kashin A.S., Ananikov V. P., Angew. Chem. Int. Ed., 2017, 56, 15931 – 15935 .
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We demonstrate the utility of 100% biomass-derived poly(ethylene-2,5-furandicarboxylate) (PEF) as an efficient material for Fused Deposition Modeling (FDM) 3D printing. A complete cycle from cellulose to printed object has been performed. PEF-printed objects created in the present study demonstrated higher chemical resistance than objects printed with commonly available materials (ABS, PLA, PETG). The studied PEF polymer has shown key advantages for 3D printing: optimal adhesion, thermoplasticity, lack of delamination and low heat shrinkage. The high thermal stability of PEF and relatively low temperature that are necessary for extrusion are optimal for recycling printed objects and minimizing waste. Several successive cycles of 3D-printing and recycling were successfully demonstrated. The suggested approach for extending additive manufacturing to carbon neutral materials opens a new direction in the field of sustainable development.

Understanding Active Species in Catalytic Transformations: from Molecular Catalysis to Nanoparticles, Leaching, “Cocktails” of Catalysts and Dynamic Systems

Eremin D.B., Ananikov V.P., Coord. Chem. Rev., 2017, 346, 2-19.
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In the present review, we consider the transformations of molecular catalysts, leaching, aggregation and various interconversions of metal complexes, clusters and nanoparticles that occur during catalytic processes. The role of catalyst evolution and the mechanistic picture of "cocktail"-type systems are considered from the perspective of the development of a new generation of efficient, selective and re-usable catalysts for synthetic applications. Rational catalyst development and the improvement of catalyst performance cannot be achieved without an understanding of the dynamic nature of catalytic systems.

Biological Activity of Ionic Liquids and Their Application in Pharmaceutics and Medicine

Egorova K.S., Gordeev E.G., Ananikov V.P., Chem. Rev., 2017, 117, 7132–7189.
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Ionic liquids are remarkable chemical compounds, which find applications in many areas of modern science. Because of their highly tunable nature and exceptional properties, ionic liquids have become essential players in the fields of synthesis and catalysis, extraction, electrochemistry, analytics, biotechnology, etc. Apart from physical and chemical features of ionic liquids, their high biological activity has been attracting significant attention from biochemists, ecologists, and medical scientists. This Review is dedicated to biological activities of ionic liquids, with a special emphasis on their potential employment in pharmaceutics and medicine. The accumulated data on the biological activity of ionic liquids, including their antimicrobial and cytotoxic properties, are discussed in view of possible applications in drug synthesis and drug delivery systems. Dedicated attention is given to a novel active pharmaceutical ingredient-ionic liquid (API-IL) concept, which suggests using traditional drugs in the form of ionic liquid species. The main aim of this Review is to attract a broad audience of chemical, biological, and medical scientists to study advantages of ionic liquid pharmaceutics. Overall, the discussed data highlight the importance of the research direction defined as "Ioliomics", studies of ions in liquids in modern chemistry, biology, and medicine.

Which Metals are Green for Catalysis? Comparison of the Toxicities of Ni, Cu, Fe, Pd, Pt, Rh, and Au Salts

Egorova K.S., Ananikov V. P., Angew. Chem. Int. Ed., 2016, 55, 12150-12162.
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Environmental profiles for the selected metals were compiled on the basis of available data on their biological activities. Analysis of the profiles suggests that the concept of toxic heavy metals and safe nontoxic alternatives based on lighter metals should be re-evaluated. Comparison of the toxicological data indicates that palladium, platinum, and gold compounds, often considered heavy and toxic, may in fact be not so dangerous, whereas complexes of nickel and copper, typically assumed to be green and sustainable alternatives, may possess significant toxicities, which is also greatly affected by the solubility in water and biological fluids. It appears that the development of new catalysts and novel applications should not rely on the existing assumptions concerning toxicity/nontoxicity. Overall, the available experimental data seem insufficient for accurate evaluation of biological activity of these metals and its modulation by the ligands. Without dedicated experimental measurements for particular metal/ligand frameworks, toxicity should not be used as a "selling point" when describing new catalysts.

Critical Influence of 5-HMF Aging and Decomposition on the Utility of Biomass Conversion in Organic Synthesis

Galkin K.I., Khokhlova E.A., Romashov L.V., Zalesskiy S.S., Kachala V.V., Burykina J.V., Ananikov V. P., Angew. Chem. Int. Ed., 2016, 55, 8338-8342.
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Spectral studies revealed the presence of a specific arrangement of 5-hydroxymethylfurfural (5-HMF) molecules in solution as a result of a hydrogen–bonding network, and this arrangement readily facilitates the aging of 5-HMF. Deterioration of the quality of this platform chemical limits its practical applications, especially in synthesis/pharma areas. The model drug Ranitidine (Zantac®) was synthesized with only 15 % yield starting from 5-HMF which was isolated and stored as an oil after a biomass conversion process. In contrast, a much higher yield of 65 % was obtained by using 5-HMF isolated in crystalline state from an optimized biomass conversion process. The molecular mechanisms responsible for 5-HMF decomposition in solution were established by NMR and ESI-MS studies. A highly selective synthesis of a 5-HMF derivative from glucose was achieved using a protecting group at O(6) position.

Direct Observation of Self-Organized Water-Containing Structures in the Liquid Phase and Their Influence on 5-(Hydroxymethyl)furfural Formation in Ionic Liquids

Kashin A.S., Galkin K.I., Khokhlova E.A., Ananikov V. P., Angew. Chem. Int. Ed., 2016, 55, 2161-2166.
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Water-containing organic solutions are widespread reaction media in organic synthesis and catalysis. This type of liquid multicomponent system has a number of unique properties due to the tendency for water to self-organize in mixtures with other liquids. In spite of key importance, the characterization of these water domains is a challenging task due to their soft and dynamic nature. In the present study, morphology and dynamics of μm-scale and nm-scale water-containing compartments in ionic liquids were directly observed by electron microscopy. A variety of morphologies, including isolated droplets, dense structures, aggregates and 2D meshwork, have been experimentally detected and studied. Using the developed method, the impact of water on the acid‑catalyzed biomass conversion reaction was studied at the microscopic level. The process that produced nanostructured domains in solution led to better yields and higher selectivities compared with reactions involving the bulk system.

Visible Light Mediated Metal-free Thiol–yne Click Reaction

Zalesskiy S.S., Shlapakov N.S., Ananikov V. P., Chem. Sci., 2016, 7, 6740-6745.
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The carbon-sulfur bond formation reaction is of paramount importance for functionalized materials design, as well as for biochemical applications. The use of expensive metal-based catalysts and the consequent contamination with trace metal impurities are challenging drawbacks of the existing methodologies. Here, we describe the first environmentally friendly metal-free photoredox pathway to the thiol–yne click reaction. Using Eosin Y as a cheap and readily available catalyst, C-S coupling products were obtained in high yields (up to 91%) and excellent selectivity (up to 60:1). A 3D-printed photoreactor was developed to create arrays of parallel reactions with temperature stabilization to improve the performance of the catalytic system.

Nature of the Copper-Oxide-Mediated C–S Cross-Coupling Reaction: Leaching of Catalytically Active Species from the Metal Oxide Surface

Panova Yu.S., Kashin A.S., Vorobev M.G., Degtyareva E.S., Ananikov V.P., ACS Catalysis, 2016, 6, 3637 – 3643.
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Copper-oxide-catalyzed cross-coupling reaction is a well-known strategy in heterogeneous catalysis. A large number of applications have been developed, and catalytic cycles have been proposed based on the involvement of the copper oxide surface. In the present work, we have demonstrated that copper(I) and copper(II) oxides served as precursors in the coupling reaction between thiols and aryl halides, while catalytically active species were formed upon unusual leaching from the oxide surface. A powerful cryo-SEM technique has been utilized to characterize the solution-state catalytic system by electron microscopy. A series of different experimental methods were used to reveal the key role of copper thiolate intermediates in the studied catalytic reaction. The present study shows an example of leaching from a metal oxide surface, where the leaching process involved the formation of a metal thiolate and the release of water. A new synthetic approach was developed, and many functionalized sulfides were synthesized with yields of up to 96%, using the copper thiolate catalyst. The study suggests that metal oxides may not act as an innocent material under reaction conditions; rather, they may represent a source of reactive species for solution-state homogeneous catalysis.

Spatial Imaging of Carbon Reactivity Centers in Pd/C Catalytic Systems

Pentsak E. O., Kashin A. S., Polynski M. V., Kvashnina K. O., Glatzel P., Ananikov V. P., Chem. Sci., 2015, 6, 3302-3313.
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Gaining insight into Pd/C catalytic systems aimed at locating reactive centers on carbon surfaces, revealing their properties and estimating the number of reactive centers presents a challenging problem. In the present study state-of-the-art experimental techniques involving ultra high resolution SEM/STEM microscopy (1 Å resolution), high brilliance X-ray absorption spectroscopy and theoretical calculations on truly nanoscale systems were utilized to reveal the role of carbon centers in the formation and nature of Pd/C catalytic materials. Generation of Pd clusters in solution from the easily available Pd 2dba3 precursor and the unique reactivity of the Pd clusters opened an excellent opportunity to develop an efficient procedure for the imaging of a carbon surface. Defect sites and reactivity centers of a carbon surface were mapped in three-dimensional space with high resolution and excellent contrast using a user-friendly nanoscale imaging procedure. The proposed imaging approach takes advantage of the specific interactions of reactive carbon centers with Pd clusters, which allows spatial information about chemical reactivity across the Pd/C system to be obtained using a microscopy technique. Mapping the reactivity centers with Pd markers provided unique information about the reactivity of the graphene layers and showed that >2000 reactive centers can be located per 1 μm2 of the surface area of the carbon material. A computational study at a PBE-D3-GPW level differentiated the relative affinity of the Pd2 species to the reactive centers of graphene. These findings emphasized the spatial complexity of the carbon material at the nanoscale and indicated the importance of the surface defect nature, which exhibited substantial gradients and variations across the surface area. The findings show the crucial role of the structure of the carbon support, which governs the formation of Pd/C systems and their catalytic activity.

Nickel: The "Spirited Horse" of Transition Metal Catalysis

Ananikov V.P., ACS Catal., 2015, 5, 1964-1971.
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In recent years, the emergence of nickel catalysis and the development of many remarkable synthetic applications have been observed. The key advantages of nickel catalysts include: a) efficient catalysis and the ability to initiate transformations involving usually unreactive substrates; b) the accessibility of Ni0/NiI/NiII/NiIII oxidation states and radical pathways; c) new reactivity patterns beyond the traditional framework of metal catalysts; d) the facile activation of unsaturated molecules and a variety of transformations involving multiple bonds; and e) opportunities in photocatalytic applications and dual photocatalysis. The present viewpoint briefly summarizes the fundamental aspects of nickel chemistry and highlights promising directions of catalyst development.

Pd-NHC Catalytic System for the Efficient Atom-Economic Synthesis of Vinyl Sulfides from Tertiary, Secondary, or Primary Thiols

Degtyareva E.S., Burykina Yu.V., Fakhrutdinov A.N., Gordeev E.G., Khrustalev V.N., Ananikov V.P., ACS Catal., 2015, 5, 7208–7213.
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Vinyl sulfides represent an important class of compounds in organic chemistry and materials science. Atom-economic addition of thiols to the triple bond of alkynes provides an excellent opportunity for environmentally friendly processes. We have found that well-known and readily available Pd-NHC complex (IMes)Pd(acac)Cl is an efficient catalyst for alkyne hydrothiolation. The reported technique provides a general one-pot approach for the selective preparation of Markovnikov-type vinyl sulfides starting from tertiary, secondary, or primary aliphatic thiols, as well as benzylic and aromatic thiols. In all the studied cases, the products were formed in excellent selectivity and good yields.

Noninnocent Nature of Carbon Support in Metal/Carbon Catalysts: Etching/Pitting vs Nanotube Growth under Microwave Irradiation

Pentsak E.O., Gordeev E.G., Ananikov V.P., ACS Catal., 2014, 4, 3806-3814.
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Microwave irradiation of Ni, Co, Cu, Ag, and Pt metal salts supported on graphite and charcoal revealed a series of carbon surface modification processes that varied depending on the conditions used (inert atmosphere, vacuum, or air) and the nature of metal salt. Carbon materials, routinely used to prepare supported metal catalysts and traditionally considered to be innocent on this stage, were found to actively change under the studied conditions: etching and pitting of the carbon surface by metal particles as well as growth of carbon nanotubes were experimentally observed by FE-SEM analysis. Catalyst preparation under microwave irradiation led to the formation of complex metal/carbon structures with significant changes in carbon morphology. These findings are of great value in developing an understanding of how M/C catalysts form and evolve and will help to design a new generation of efficient and stable catalysts. The energy surfaces of carbon support modification processes were studied with theoretical calculations at the density functional level. The energy surface of the multistage process of carbon nanotube formation from an etched graphene sheet was calculated for various types of carbon centers. These calculations indicated that interconversion of graphene layers and single wall carbon nanotubes is possible when cycloparaphenylene rings act as building units.

Miniaturization of NMR Systems: Desktop Spectrometers, Microcoil Spectroscopy, and "NMR on a Chip" for Chemistry, Biochemistry, and Industry

Zalesskiy S.S., Danieli E., Blümich B., Ananikov V. P., Chem. Rev., 2014, 114, 5641-5694.
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Efficient General Procedure To Access a Diversity of Gold(0) Particles and Gold(I) Phosphine Complexes from a Simple HAuCl4 Source. Localization of Homogeneous/Heterogeneous System's Interface and Field-Emission Scanning Electron Microscopy Study

Zalesskiy S. S., Sedykh A. E., Kashin A. S., Ananikov V. P., J. Am. Chem. Soc., 2013, 135, 3550-3559.
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Soluble gold precatalysts, aimed for homogeneous catalysis, under certain conditions may form nanoparticles, which dramatically change the mechanism and initiate different chemistry. The present study addresses the question of designing gold catalysts, taking into account possible interconversions and contamination at the homogeneous/heterogeneous system's interface. It was revealed that accurate localization of boundary experimental conditions for formation of molecular gold complexes in solution versus nucleation and growth of gold particles opens new opportunities for well-known gold chemistry. Within the developed concept, a series of practical procedures was created for efficient synthesis of soluble gold complexes with various phosphine ligands (R3P)AuCl (90–99% yield) and for preparation of different types of gold materials. The effect of the ligand on the particles growth in solution has been observed and characterized with high-resolution field-emission scanning electron microscopy (FE-SEM) study. Two unique types of nanostructured gold materials were prepared: hierarchical agglomerates and gold mirror composed of ultrafine smoothly shaped particles.