Stabilization of the Pd-NHC framework with 1,2,4-triazol-5-ylidene ligands toward decomposition in alkaline media.
Andrey Chernenko, Vadim Kutyrev, Evgenyi Gordeev, Julia Burykina, Mikhail Minyaev, Victor Khrustalev, Victor Chernyshev, Valentine Ananikov.
Inorganic Chemistry Frontiers, 2021

Complexes of Pd(II) with NHC ligands can suffer facile decomposition in the presence of alkali metal hydroxides, alkoxydes and other strong oxygen-containing bases via the reductive elimination of the NHC and Pd-coordinated base anion, the so-called O–NHC coupling. O–NHC coupling can represent a serious problem for the stability of Pd/NHC catalytic systems in numerous practically important reactions conducted in the presence of bases. In the present study, a new approach to stabilizing the Pd–NHC bond against cleavage by strong bases was developed. The approach relies on the installation of an NH–acidic RNH substituent at position 3 of the triazole ring of the 1,2,4-triazol-5-ylidene ligand. A series of new Pd/NHCs containing RNH substituents (R = Ac, Ph, alkyl) in triazole NHC ligands were synthesized. These complexes undergo reversible deprotonation of the RNH group in strong alkaline media and demonstrate superior stability of the Pd–NHC bond, significantly higher than complexes of similar structure without the RNH group. DFT calculations revealed that the anionic Pd/NHC complex containing an N-deprotonated acetamido group (R = Ac) is more kinetically stable against O–NHC coupling and less prone to lose NHC via heterolytic dissociation of the Pd–NHC bond than the neutral complex. The new complexes with RNH-functionalized NHC ligands were tested as precatalysts in the Suzuki–Miyaura coupling of p-tolyl bromide with phenylboronic acid in the presence of KOH and revealed more than 2 times higher TONs than similar complexes without the RNH group or ligandless Pd system.
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Ni/NHC catalysis in C–H functionalization using air-tolerant nickelocene and sodium formate for in situ catalyst generation.
Oleg Khazipov, Konstantin Shepelenko, Dmitry Pasyukov, Vasilii Chesnokov, Safarmurod Soliev, Victor Chernyshev, Valentine Ananikov
Organic Chemistry Frontiers, 2021

C–H functionalization in the area of fine organic synthesis is dominated by noble metal catalysts, which represent the most expensive and least sustainable options. Sustainable C–H functionalization may involve Ni catalysts. However, Ni(0) complexes are unstable under regular conditions and are more difficult to obtain as compared to Pd(0) or Rh(I). In the present study, a facile method for Ni0/NHC-catalyzed C–H alkylation and alkenylation of heteroarenes with alkenes and internal alkynes is presented. This method relies on the in situ generation of Ni0/NHC complexes from air-tolerant bench-stable precursors, Ni(Cp)2, NHC·HCl salts and sodium formate. The optimized catalytic system demonstrates broad substrate scope and high selectivity (>60 products were obtained in up to 99% isolated yield). The approach represents a user-friendly alternative for air-sensitive and labile (NHC)Ni0 and Ni(COD)2 precatalysts or complexes. The intermediates involved in the catalytic system were investigated and possible decomposition routes were mapped with NMR and ESI-MS. Rational control over the catalyst decomposition pathways further strengthens the sustainability of the procedure.
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Formation and stabilization of nanosized Pd particles in catalytic systems: Ionic nitrogen compounds as catalytic promoters and stabilizers of nanoparticles.
Victor Chernyshev, Oleg Khazipov, Dmitry Eremin, Ekaterina Denisova, Valentine Ananikov
Coordination Chemistry Reviews, Volume 437, 15 June 2021

Actual palladium catalysts in synthetic transformations in reaction mixtures are usually represented by dynamic catalytic systems that contain various interconvertible forms of metal particles, including molecular complexes, metal clusters, and nanoparticles. The low thermodynamic stability of Pd nanoparticles can lead to their aggregation and, as a consequence, to the deactivation of the catalytic systems. Therefore, stabilization of nanosized Pd particles is of key importance to ensure efficient catalysis. This review discusses the main pathways for the formation of Pd nanoparticles and clusters from various precatalysts in catalytic systems, as well as current views on the mechanisms of stabilization of these nanosized Pd particles using various types of ionic nitrogen compounds, such as ammonium, amidinium, azolium, and pyridinium salts. The use of ionic nitrogen compounds as specially added or in situ formed stabilizers, ligands, catalytic promoters, heterogenized catalysts (supported ionic liquid phase, SILP) and reaction media (ionic liquids) is exemplified by several important catalytic reactions. The main effects of ionic nitrogen compounds on catalytic processes are also discussed, including possible involvement in catalytic cycles and unwanted side reactions.
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Different effects of metal-NHC bond cleavage on the Pd/NHC and Ni/NHC catalyzed α-arylation of ketones with aryl halides.
Konstantin Shepelenko, Safarmurod Soliev, Alexey Galushko, Viktor Chernyshev, Valentine Ananikov
Inorg. Chem. Front., 2021

Recently, the dynamic nature of the metal-NHC bond has been proposed and the key role of chemical evolution in changing the nature of catalytically active sites is now an emerging topic. A comparative analysis of the ketone α-arylation reaction with aryl halides, catalyzed by M/NHC complexes, was carried out in the present study and showed a fundamental difference in the behavior of the catalytic system for M = Ni and Pd. In situ evolution of Ni/NHC complexes with cleavage of the Ni-NHC bond leads to complete deactivation of catalytic systems, regardless of the nature of the aryl halide ArX (X = Cl, Br, I). However, upon Pd/NHC catalysis, the cleavage of the Pd-NHC bond causes deactivation only in the case of aryl chlorides. In the reactions of more active aryl iodides and aryl bromides, NHC-disconnected Pd species, formed as a result of the chemical transformation of Pd/NHC complexes, can provide effective catalysis in the arylation reaction under study. New catalytic systems based on Pd/NHC and Ni/NHC complexes generated in situ from stable imidazolium salts, IPr·HCl and IPr*OMe·HCl, and Pd(OAc)2 (0.1 mol%) or NiCl2Py2 (5 mol%) were developed for the selective α-arylation of methylaryl ketones (Pd-catalysis) and other ketones less prone to aldol-crotonic condensation (Ni-catalysis). The present study has shown that the different effects of the metal-NHC bond cleavage should be taken into account for the efficient choice and optimization of catalytic systems to carry out arylation reaction with various aryl halides.
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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.
Victor Chernyshev, Ekaterina Denisova, Dmitry Eremin, Valentine Ananikov
Chem. Sci., 2020, Vol. 11, pp 6957-6977

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.
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Preventing Pd-NHC bond cleavage and switching from nano-scale to molecular catalytic systems: amines and temperature as catalyst activators.
Oleg Khazipov, Maxim Shevchenko, Dmitry Pasyukov, Andrey Chernenko, Alexander Astakhov, Viktor Tafeenko, Victor Chernyshev, Valentine Ananikov
Catal. Sci. Technol., 2020, Vol. 10, pp 1228-1247

Many reactions catalyzed by Pd complexes with N-heterocyclic carbene (NHC) ligands are performed in the presence of amines which usually act as coupling reagents or mild bases. However, amines can react with Pd/NHC complexes in a number of ways: enhancing molecular catalysis, causing the catalyst deactivation or triggering the ligandless modes of catalysis by producing NHC-free active palladium species. This study gains insight into conditions required for the efficient use of amines as activators of molecular Pd/NHC catalysis and preventing the undesirable reductive cleavage of the Pd-NHC bond in catalytic systems. Reactions of Pd/NHC complexes with various amines within a temperature range of 25–140 °C and thermal stability of the resulting amino-complexes are examined. The results indicate the major influence of the amine structure and reaction temperature on the catalyst transformations. In particular, thermal decomposition of Pd/NHC complexes with aliphatic amine ligands predominantly leads to the reductive Pd-NHC bond cleavage, while deprotonation of the complexes with primary and secondary aliphatic amine ligands in the presence of strong bases at 25–60 °C promotes the activation of molecular Pd/NHC catalysis. Efficient Pd-PEPPSI complex – amine systems suitable for the strong-base-promoted C-S cross-coupling reactions between aryl halides and thiols are suggested on the basis of these findings.
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Relative Stability of M/NHC Complexes (M = Ni, Pd, Pt) against R−NHC, X−NHC and X−X Couplings in M(0)/M(II) and M(II)/M(IV) Catalytic Cycles: a Theoretical Study.
Alexander Astakhov, Safarmurod Soliev, Evgeniy Gordeev, Victor Chernyshev, Valentine Ananikov
Dalton Trans., 2019, Vol. 48, pp 17052-17062

Complexes of Ni, Pd, and Pt with N-heterocyclic carbenes (NHCs) catalyze numerous organic reactions via typically proposed M0/MII catalytic cycles comprising intermediates with the metal center in (0) and (II) oxidation states. In addition, MII/MIV catalytic cycles have also been proposed for a number of reactions. Catalytic intermediates in both cycles can suffer decomposition via R-NHC coupling, the side reductive elimination of NHC ligand and R groups (R = alkyl, aryl, etc.) to give [NHC-R]+ cations. In this study, relative stability of (NHC)MII(R)(X)L and (NHC)MIV(R)(X)3L intermediates (X = Cl, Br, I; L = NHC, pyridine) against the R-NHC coupling and other decomposition pathways via reductive elimination reactions is evaluated theoretically. The study reveals that R-NHC coupling represents the most favorable decomposition pathway for both types of intermediates (MII and MIV), while it is thermodynamically and kinetically more facile for the MIV complexes. Relative effects of the metal M (Ni, Pd, Pt), ligands L and X on the R-NHC coupling for the MIV complexes are significantly stronger than for the MII complexes. In particular, for (NHC)2MIV(Ph)(Br)3 complexes, Ph-NHC coupling is facilitated dramatically from Pt (ΔG = -36.9 kcal/mol, ΔG≠ = 37.5 kcal/mol) to Pd (ΔG = -61.5 kcal/mol, ΔG≠ = 18.3 kcal/mol) and Ni (ΔG = -80.2 kcal/mol, ΔG≠ = 4.7 kcal/mol). For the MII oxidation state of the metal, bis-NHC complexes (L = NHC) are kinetically and thermodynamically slightly more stable against R-NHC coupling than the mono-NHC complexes (L = pyridine). The inverse relation is observed for the MIV oxidation state of the metal, as (NHC)2MIV(R)(X)3 complexes are kinetically (4.3-15.9 kcal/mol) and thermodynamically (8.0-23.2 kcal/mol) significantly less stable than the (NHC)MIV(R)(X)3L (L =pyridine) complexes. For NiIV and PdIV complexes, additional decomposition pathways via the reductive elimination of NHC and X ligand to give [NHC-X]+ cation (X-NHC coupling) or reductive elimination of X-X molecule are found to be thermodynamically and kinetically probable. In overall, the obtained results demonstrate significant instability of regular Ni/NHC and Pd/NHC complexes (for example, not stabilized additionally by chelation) and high probability to initiate "NHC-free" catalysis in the reactions comprising MIV intermediates.
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Ionic Pd/NHC Catalytic System Enables Recoverable Homogeneous Catalysis. Mechanistic Study and Application in the Mizoroki‐Heck Reaction.
Dmitry Eremin, Ekaterina Denisova, Alexander Kostyukovich, Jonathan Martens, Giel Berden, Jos Oomens, Victor Khrustalev, Victor Chernyshev, Valentine Ananikov
Chemistry - A European Journal, 2019, Vol. 25, pp 16564–16572

N‐Heterocyclic carbene ligands (NHC) are ubiquitously utilized in catalysis. A common catalyst design model assumes strong M‐NHC binding in this metal‐ligand framework. In contrast to this common assumption, we demonstrate here that lability and controlled cleavage of the M‐NHC bond (rather than its stabilization) could be more important for high‐performance catalysis at low catalyst concentrations. The present study reveals a dynamic stabilization mechanism with labile metal‐NHC binding and [PdX3]–[NHC‐R]+ ion pair formation. Access to reactive anionic palladium intermediates formed by dissociation of the NHC ligands and plausible stabilization of the molecular catalyst in solution by interaction with the [NHC‐R]+ azolium cation is of particular importance for an efficient and recyclable catalyst. These ionic Pd/NHC complexes allowed for the first time the recycling of the complex in a well‐defined form with isolation at each cycle. Computational investigation of the reaction mechanism confirms a facile formation of NHC‐free anionic Pd in polar media via either Ph‐NHC coupling or reversible H‐NHC coupling. The present study formulates novel ideas for M/NHC catalyst design.
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Pd and Pt Catalyst Poisoning in the Study of Reaction Mechanisms: What Does the Mercury Test Mean for Catalysis?
Victor Chernyshev, Alexander Astakhov, Ilya Chikunov, Roman Tyurin, Dmitry Eremin, Gleb Ranny, Victor Khrustalev, Valentine Ananikov
ACS Catalysis, 2019, Vol. 9, pp 2984–2995

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 M0 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.
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Revealing the unusual role of bases in activation/deactivation of catalytic systems: O–NHC coupling in M/NHC catalysis.
Victor Chernyshev, Oleg Khazipov, Maxim Shevchenko, Andrey Chernenko, Alexander Astakhov, Dmitry Eremin, Dmitry Pasyukov, Alexey Kashin, Valentine Ananikov
Chemical Science, 2018, Vol. 9, (25), pp 5564-5577

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.
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Fast and Slow Release of Catalytically Active Species in Metal/NHC Systems Induced by Aliphatic Amines.
Oleg Khazipov, Maxim Shevchenko, Andrey Chernenko, Alexander Astakhov, Dmitry Pasyukov, Dmitry Eremin, Yan Zubavichus, Victor Khrustalev, Victor Chernyshev, Valentine Ananikov
Organometallics, 2018, Vol. 37, (9), pp 1483–1492

The behavior of ubiquitously used nickel, palladium, and platinum complexes containing N-heterocyclic carbene ligands was studied in solution in the presence of aliphatic amines. Transformation of M(NHC)X2L complexes readily occurred according to the following reactions: (i) release of the NHC ligand in the form of azolium salt and formation of metal clusters or nanoparticles and (ii) isomerization of mono-NHC complexes M(NHC)X2L to bis-NHC derivatives M(NHC)2X2. Facile cleavage of the M–NHC bond was observed and provided the possibility for fast release of catalytically active NHC-free metal species. Bis-NHC metal complexes M(NHC)2X2were found to be significantly more stable and represented a molecular reservoir of catalytically active species. Slow decomposition of the bis-NHC complexes by removal of the NHC ligands (also in the form of azolium salts) occurred, generating metal clusters or nanoparticles. The observed combination of dual fast- and slow-release channels is an intrinsic latent opportunity of M/NHC complexes, which balances the activity and durability of a catalytic system. The fast release of catalytically active species from M(NHC)X2L complexes can rapidly initiate catalytic transformation, while the slow release of catalytically active species from M(NHC)2X2 complexes can compensate for degradation of catalytically active species and help to maintain a reliable amount of catalyst. The study clearly shows an outstanding potential of dynamic catalytic systems, where the key roles are played by the lability of the M–NHC framework rather than its stability.
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Sustainable Utilization of Biomass Refinery Wastes for Accessing Activated Carbons and Supercapacitor Electrode Materials.
Daria Chernysheva, Yuri Chus, Victor Klushin, Tatiana Lastovina, Lyudmila Pudova, Nina Smirnova, Oleg Kravchenko, Victor Chernyshev, Valentine Ananikov
ChemSusChem, 2018, Vol. 11, pp 3599–3608

Biomass processing wastes (humins) are anticipated to become a large‐tonnage solid waste in the near future, owing to the accelerated development of renewable technologies based on utilization of carbohydrates. In this work, the utility of humins as a feedstock for the production of activated carbon by various methods (pyrolysis, physical and chemical activation, or combined approaches) was evaluated. The obtained activated carbons were tested as potential electrode materials for supercapacitor applications and demonstrated combined micro‐ and mesoporous structures with a good capacitance of 370 F g−1 (at a current density of 0.5 A g−1) and good cycling stability with a capacitance retention of 92 % after 10 000 charge/discharge cycles (at 10 A g−1 in 6 m aqueous KOH electrolyte). The applicability of the developed activated carbon for practical usage as a supercapacitor electrode material was demonstrated by its successful utilization in symmetric two‐electrode cells and by powering electric devices. These findings provide a new approach to deal with the problem of sustainable wastes utilization and to advance challenging energy storage applications.
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Base-free aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over Pt/C catalysts synthesized by pulse alternating current technique.
Daria Chernysheva, Victor Klushin, Alexander Zubenko, Lyudmila Pudova, Oleg Kravchenko, Victor Chernyshev, Nina Smirnova
Mendeleev Communications, 2018, Vol. 28, (4), pp 431-433

The Pt/C catalysts with various Pt content (5-30 wt%) synthesized viaelectrochemical pulse alternating current technique have been evaluated for the base-free aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid. The higher Pt content in the catalyst (30 wt%) provides the product yield up to 65% upon performing the process in concentrated (∼0.1 M) aqueous solutions of the substrate.
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Influence of R–NHC Coupling on the Outcome of R–X Oxidative Addition to Pd/NHC Complexes (R = Me, Ph, Vinyl, Ethynyl).
Evgeniy Gordeev, Dmitry Eremin, Victor Chernyshev, Valentine Ananikov
Organometallics, 2018, Vol. 37 (5), pp 787–796

Oxidative addition of organic halides (R–X) to (NHC)Pd0L complexes is involved in numerous metal-catalyzed reactions, and this step is expected to afford (NHC)PdII(R)(X)L intermediate complexes. However, these complexes may undergo further transformation via R–NHC coupling, which removes the NHC ligands from the metal and results in the generation of "bare" NHC-free metal species. The comparative theoretical study carried out in the present work revealed that the kinetic and thermodynamic stability of the (NHC)PdII(R)(X)L oxidative addition intermediates depends strongly on the nature of the organic group R. The predicted reactivity in the R–NHC coupling process decreases in the following order: R = Vinyl > Ethynyl > Ph > Me. Accordingly, for R = Me, a classical (NHC)PdII(R)(X)L intermediate can be expected as a product of the oxidative addition step, whereas for R = Ph, the outcome of the oxidative addition may already contain the NHC-free palladium complex. For R = Ethynyl, comparable amounts of both complexes should be formed, while for R = Vinyl, the NHC-free palladium complex can be the major product of the oxidative addition process. Unusual thermodynamic and kinetic instability of the (NHC)Pd(vinyl)(X)L complex and the tendency to vinyl–NHC coupling predicted by the computational modeling has been confirmed by experimental measurements with online mass spectrometric reaction monitoring. Thus, the outcome of the oxidative addition strongly depends on the type of organic group R and the R–NHC coupling process greatly influences the activity and stability of metal catalysts.
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Ten-fold boost of catalytic performance in thiol–yne click reaction enabled by a palladium diketonate complex with a hexafluoroacetylacetonate ligand.
Dmitry Eremin, Daniil Boiko, Eugenia Borkovskaya, Victor Khrustalev, Victor Chernyshev, Valentine Ananikov
Catalysis Science & Technology, 2018, Vol. 8, (12), pp 3073-3080

Palladium complexes with fluorinated acetylacetonate chelating ligands were studied as catalysts for alkyne hydrothiolation. A ten-fold increase in the catalytic efficiency was achieved by using 0.1 mol% of Pd(hfpd)2complex (hfpd = hexafluoroacetylacetonate) with a variety of thiol–yne coupling partners. The principal possibility of a hundred-fold increase in the efficiency of Pd-catalyzed Markovnikov-type RSH addition with 0.01 mol% of the catalyst was successfully achieved with the hfpd ligand for the first time. The hexafluoroacetylacetonate chelating ligand not only enhanced the affinity of palladium centers to the triple bond of acetylene, but also stabilized the catalytic system against formation of insoluble polymeric [Pd(SPh)2]nspecies, thus ensuring that the reaction operates homogeneously. Utilizing other diketonate ligands resulted in cocktail-type catalysis with variable and poorly predictable contributions of homogeneous and heterogeneous pathways.
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Chlorotrimethylsilane-promoted synthesis of 1,2,4-triazolopyrimidines from 3,5-diamino-1,2,4-triazoles and pentane-2,4-diones.
Alexander Astakhov, Kyrill Suponitsky, Victor Chernyshev
Mendeleev Communications, 2018, Vol. 28, (4) pp 439-441

An efficient synthesis of 2-amino-1-R-[1,2,4]triazolo[1,5-a]-pyrimidinium or 3-amino-2-R-[1,2,4]triazolo[4,3-a]pyrimidi- nium chloride derivatives by heterocyclization of 3,5-diamino-1-R-1,2,4-triazoles (R = Alk or Ar) with pentane-2,4-diones was developed. The process is promoted by chlorotrimethyl- silane which plays the dual role of carbonyl-activating agent and water scavenger.
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A TEMPO-like nitroxide combined with an alkyl-substituted pyridine: An efficient catalytic system for the selective oxidation of alcohols with iodine.
Vera Kashparova, Victor Klushin, Irina Zhukova, Igor Kashparov, Daria Chernysheva, Irina Il'chibaeva, Nina Smirnova, Efim Kagan, Victor Chernyshev
Tetrahedron Letters, 2017, Vol. 58, (36), pp 3517-3521

An efficient method for the oxidation of alcohols to aldehydes or ketones in a two-phase CH2Cl2/NaHCO3 (aq.) system, using iodine and catalytic amounts of 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl and 2,4,6-trimethylpyridine, was developed. The performance of the method was demonstrated by the selective oxidation of 37 variously substituted alcohols in ≥90% yield, including the gram-scale synthesis of the important chemical 2,5-diformylfuran from biomass-derived 5-hydroxylmethylfurfural.
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A New Mode of Operation of Pd-NHC Systems Studied in a Catalytic Mizoroki–Heck Reaction.
Alexander Astakhov, Oleg Khazipov, Andrey Chernenko, Dmitry Pasyukov, Alexey Kashin, Evgeniy Gordeev, Victor Khrustalev, Victor Chernyshev, Valentine Ananikov
Organometallics, 2017, Vol. 36 (10), pp 1981–1992

Metal complexes bearing N-heterocyclic carbene (NHC) ligands are typically considered the system of choice for homogeneous catalysis with well-defined molecular active species due to their stable metal–ligand framework. A detailed study involving 19 different Pd-NHC complexes with imidazolium, benzimidazolium, and triazolium ligands has been carried out in the present work and revealed a new mode of operation of metal-NHC systems. The catalytic activity of the studied Pd-NHC systems is predominantly determined by the cleavage of the metal–NHC bond, while the catalyst performance is strongly affected by the stabilization of in situ formed metal clusters. In the present study, the formation of Pd nanoparticles was observed from a broad range of metal complexes with NHC ligands under standard Mizoroki–Heck reaction conditions. A mechanistic analysis revealed two different pathways to connect Pd-NHC complexes to "cocktail"-type catalysis: (i) reductive elimination from a Pd(II) intermediate and the release of NHC-containing byproducts and (ii) dissociation of NHC ligands from Pd intermediates. Metal-NHC systems are ubiquitously applied in modern organic synthesis and catalysis, while the new mode of operation revealed in the present study guides catalyst design and opens a variety of novel opportunities. As shown by experimental studies and theoretical calculations, metal clusters and nanoparticles can be readily formed from M-NHC complexes after formation of new M–C or M–H bonds followed by C–NHC or H–NHC coupling. Thus, a combination of a classical molecular mode of operation and a novel cocktail-type mode of operation, described in the present study, may be anticipated as an intrinsic feature of M-NHC catalytic systems.
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Conversion of plant biomass to furan derivatives and sustainable access to the new generation of polymers, functional materials and fuels.
Victor Chernyshev, Oleg Kravchenko, Valentine Ananikov
Russian Chemical Reviews, 2017, Vol. 86, (5), pp 357-387

5-Hydroxymethylfurfural (HMF) is an important versatile reagent, a so-called platform chemical, that can be produced from plant biomass compounds: hexose carbohydrates and lignocellulose. In the near future, HMF and its derivatives could become an alternative feedstock for the chemical industry and replace, to a great extent, non-renewable sources of hydrocarbons (oil, natural gas and coal). This review analyzes recent advances in the synthesis of HMF from plant feedstocks and considers the prospects for the use of HMF in the production of monomers and polymers, porous carbon materials, engine fuels, solvents, pharmaceuticals, pesticides and chemicals. The most important HMF derivatives considered in the review include 2,5-furandicarboxylic acid, 2,5-diformylfuran, 2,5-bis(hydroxymethyl)furan, 2,5-bis(aminomethyl)furan, 2,5-dimethylfuran, 2,5-dimethyltetrahydrofuran, 2,5-bis(methoxymethyl)furan, and 5-ethoxymethylfurfural. In the nearest future, a significant extension of the HMF application is expected, and this platform chemical may be considered a major source of carbon and hydrogen for the chemistry of the 21st century.
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The impact of Al2O3 promoter on an efficiency of C5+ hydrocarbons formation over Co/SiO2 catalysts via Fischer-Tropsch synthesis.
Alexander Savost'yanov, Roman Yakovenko, Sergey Sulima, Vera Bakun, Grigoriy Narochnyi, Victor Chernyshev, Sergey Mitchenko
Catalysis Today, 2017, Vol. 279, (1), pp 107-114

The influence of doping of Co/SiO2 catalysts with alumina on a performance of Fischer-Tropsch synthesis (FTS) was studied by extended FTS trials in a fixed-bed tubular pilot-scaled reactor. The addition of small amount of Al2O3 causes apparent promotional effect on the catalysts activity and C5+ hydrocarbons selectivity. The largest promotion effect was observed for the catalysts with 1 wt.% of alumina loading. The modification of the catalyst with alumina (1 wt.%) changes molecular weight distribution of the resultant C5+ paraffins with increasing the fraction of C8–C25 and decreasing the fraction of longer chain hydrocarbons. The addition of a proper amount of alumina into Co/SiO2 catalyst alters Co° particle size distribution making it narrower with the maximum at 8 nm and the same mean value for Co° particle size. A volcano-like dependence of CO chemisorption on alumina loadings with a maximum at 1 wt.% was observed. Relatively high CO chemisorption at the proper amount of alumina decreases the ratio of surface hydrogen to carbon monoxide and in such a way promotes formation of C5+ hydrocarbons.
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Alkoxy base-mediated selective synthesis and new rearrangements of 1,2,4-triazolodipyrimidinones.
Dmitry Pyatakov, Alexander Astakhov, Andrey Sokolov, Artem Fakhrutdinov, Andrew Fitch, Victor Rybakovd, Vladimir Chernyshev, Victor Chernyshev
Tetrahedron Letters, 2017, Vol. 58, (8), pp 748-754

A versatile approach for the synthesis of [1,2,4]triazolodipyrimidinones with various annulations of the triazole and pyrimidine rings was developed. The isomeric triazolodipyrimidinones were obtained by the stepwise condensation of partially hydrogenated [1,2,4]triazolo[1,5-a]pyrimidin-2-amines with β-ketoesters or diethyl ethoxymethylenemalonate, alkoxy base-mediated cyclization of the enamines, and subsequent cascade rearrangement of the 10-oxo-[1,2,4]triazolo[1,5-a:4,3-a′]dipyrimidines.
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Reactivity of C-Amino-1,2,4-triazoles toward Electrophiles: A Combined Computational and Experimental Study of Alkylation by Halogen Alkanes.
Victor Chernyshev, Anna Vlasova, Alexander Astakhov, Svitlana Shishkina, Oleg Shishkin
The Journal of Organic Chemistry, 2015, Vol. 80 (1), pp 375–385

A combination of computational and experimental methods was used to examine the structure–reactivity relationships in the reactions of C-amino-1H-1,2,4-triazoles with electrophiles. The global nucleophilicity of 3-amino- and 3,5-diamino-1H-1,2,4-triazoles was predicted to be higher than that of 5-amino-1H-1,2,4-triazoles. Fukui functions and molecular electrostatic potential indicate that reactions involving an amino group should occur more easily for the 3-amino- than for the 5-amino-1H-1,2,4-triazoles. Increasing electrophile hardness should increase the probability of attack at the N-4 atom of the triazole ring, whereas increasing softness should enhance the probability of attack at the N-2 atom and 3-NH2 group. Calculated transition state energies of model SN2 reactions and experimental studies showed that quaternization of 1-substituted 3-amino- and 3,5-diamino-1H-1,2,4-triazoles by many alkyl halides proceeds with low selectivity and can involve the N-2 and N-4 atoms as well as the 3-NH2 group as reaction centers. A new method for the selective synthesis of 1,4-disubstituted 3-amino- and 3,5-diamino-1,2,4-triazoles based on quaternization of readily available 1-substituted 3-acetylamino-1,2,4-triazoles with subsequent removal of the acetyl protecting group by acid hydrolysis was developed.
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A Direct Approach to a 6-Hetarylamino[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazine Library.
Nadezhda Palysaeva, Katerina Kumpan, Marina Struchkova, Igor Dalinger, Aleksandr Kormanov, Nataly Aleksandrova, Victor Chernyshev, Dmitrii Pyreu, Kyrill Suponitsky, Aleksei Sheremetev
Organic Letters, 2014, Vol. 16 (2), pp 406–409

The synthesis of 6-hetarylamino[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazines is reported. The functionalized secondary amines were constructed via a K2CO3-mediated SNAr reaction of weakly basic hetarylamines with 3-(3,5-dimethylpyrazol-1-yl)[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazines, which allowed displacement 3,5-dimethylpyrazolyl leaving group. Significantly, the reaction exhibited a broad substrate scope and proceeded in good yields.
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Partially hydrogenated 2-amino[1,2,4]triazolo[1,5-a]pyrimidines as synthons for the preparation of polycondensed heterocycles: reaction with chlorocarboxylic acid chlorides.
Victor Chernyshev, Dmitry Pyatakov, Andrey Sokolov, Alexander Astakhov, Eugene Gladkov, Svetlana Shishkina, Oleg Shishkin
Tetrahedron, 2014, Vol. 70 (3), pp 684-701

Partially hydrogenated 2-amino[1,2,4]triazolo[1,5-a]pyrimidines and 2-amino[1,2,4]triazolo[5,1-b]quinazolines react with the chlorides of chloroacetic, 3-chloropropanoic, and 4-chlorobutanoic acids at 0–5 °C to give amides through acylation of the 2-amino group. Heating the corresponding 3-chloropropanoyl derivatives at 80–90 °C in DMF leads to selective intramolecular alkylation at N-3 to form the chlorides of partially hydrogenated [1,2,4]triazolo[1,5-a:4,3-a′]dipyrimidin-5-ones and pyrimido[2′,1′:3,4][1,2,4]triazolo[5,1-b]quinazolin-12-ones. It may be more convenient to prepare such compounds through one-pot processes. Some reactions of the synthesized chlorides of polycondensed heterocycles have been studied. Conditions have been found to effect the selective synthesis of free bases, oxidative aromatization or hydrolysis of the dihydropyrimidine cycle, and the selective hydrolytic cleavage or elimination of the pyrimidone ring. Some of the resulting compounds represent new mesoionic heterocycles.
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