Catalytic Adaptive Recognition of Thiol (SH) and Selenol (SeH) Groups Towards Synthesis of Functionalized Vinyl Monomers

Ananikov V. P., Orlov N. V., Zalesskiy S. S., Beletskaya I. P., Khrustalev V. N., Morokuma K., Musaev D. G., J. Am. Chem. Soc., 2012, 134, 6637-6649.
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An unprecedented sustainable procedure was developed to produce functionalized vinyl monomers H2C═C(R)(FG) starting from a mixture of sulfur and selenium compounds as a functional group donor (FG = S or Se). The reaction serves as a model for efficient utilization of natural resources of sulfur feedstock in oil and technological sources of sulfur/selenium. The catalytic system is reported with amazing ability to recognize SH/SeH groups in the mixture and selectively incorporate them into valuable organic products via wastes-free atom-economic reaction with alkynes (HC≡CR). Formation of catalyst active site and the mechanism of the catalytic reaction were revealed by joint experimental and theoretical study. The difference in reactivity of μ1- and μ2-type chalcogen atoms attached to the metal was established and was shown to play the key role in the action of palladium catalyst. An approach to solve a challenging problem of dynamically changed reaction mixture was demonstrated using adaptive tuning of the catalyst. The origins of the adaptive tuning effect were investigated at molecular level and were found to be governed by the nature of metal–chalcogen bond.

Toward the Ideal Catalyst: From Atomic Centers to a "Cocktail" of Catalysts

Ananikov V. P., Beletskaya I. P., Organometallics, 2012, 31, 1595-1604.
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The current state of the art and perspectives of homogeneous and heterogeneous catalysis are discussed for C–C and C–heteroatom bond formation in organic synthesis. The relationship between catalyst centers represented by a single metal atom and by multiple metal atoms is considered for reactions taking place in solution. The influence of leaching and catalyst evolution in the liquid phase on the activity, selectivity, and stability of the catalyst is highlighted from a mechanistic point of view. Metal nanoparticle and "nanosalt" types of catalysts are compared for constructing new C–C and C–heteroatom bonds.

The First Molecular Level Monitoring of Carbohydrate Conversion to 5-Hydroxymethylfurfural in Ionic Liquids. B2O3 - An Efficient Dual-Function Metal-Free Promoter for Environmentally Benign Applications

Khokhlova E. A., Kachala V. V., Ananikov V. P., ChemSusChem, 2012, 5, 783-789.
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The mechanistic nature of the conversion of carbohydrates to the sustainable platform chemical 5-hydroxymethylfurfural (5-HMF) was revealed at the molecular level. A detailed study of the key sugar units involved in the biomass conversion process has shown that the simple dissolution of fructose in the ionic liquid 1-butyl-3-methylimidazolium chloride significantly changes the anomeric composition and favors the formation of the open fructoketose form. A special NMR approach was developed for the determination of molecular structures and monitoring of chemical reactions directly in ionic liquids. The transformation of glucose to 5-HMF has been followed in situ through the detection of intermediate species. A new environmentally benign, easily available, metal-free promoter with a dual functionality (B2O3) was developed for carbohydrate conversion to 5-HMF.

Pd2(dba)3 as a Precursor of Soluble Metal Complexes and Nanoparticles: Determination of Palladium Active Species for Catalysis and Synthesis

Zalesskiy S. S., Ananikov V. P., Organometallics, 2012, 31, 2302-2309.
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Tris(dibenzylideneacetone)dipalladium (Pd2(dba)3) is ubiquitously used as a source of soluble Pd species for catalysis and as a precursor in the synthesis of more complex Pd structures. In spite of the massive usage of this convenient Pd complex, its nature in solution has not been revealed in detail and the applications rely on the assumed state and purity of the compound. In the present study we have developed a convenient NMR procedure to reveal the nature of Pd2(dba)3 and to determine the purity of the complex. Surprisingly, it was found that commercially available samples of Pd2(dba)3 may readily contain up to 40% of Pd nanoparticles in a wide range of sizes (10–200 nm). The study has shown that the routinely accepted practice of utilization of Pd2(dba)3 without analysis of the purity (both commercially available and prepared by common procedures) can introduce significant errors in the estimation of catalyst efficiency and lead to incorrect values of TON, TOF, and reported mol % values in the catalytic procedures. The presence of Pd nanoparticles in the catalyst precursor provides an opportunity for heterogeneous catalytic systems of different nature to be directly accessible from Pd2(dba)3. In the present study we report a modified procedure for the synthesis of Pd2(dba)3CHCl3 with 99% purity.

Linear Encoding of Functional Groups in the Synthesis of Heterocyclic Compounds: Cycloaddition of Enyne and Alkyne Units

Ananikov V. P., Chem. Heterocycl. Compd., 2012, 1, 7-11.
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A family of novel [4+2]-cycloaddition reactions is discussed to carry out efficient preparation of poly-substituted heterocyclic compounds in a single-step starting with linear precursors. High selectivity of the intramolecular transformation and pre-defined position of substituents in the product were governed by linear encoding in the structure of starting reagents. The designed reactions utilized green chemistry potential of cycloaddition approach and provided a convenient synthetic route to cyclopentapyridines, indoles,isoindoles, indolizines, isophosphindoles, benzofurans, benzothiophenes, benzoselenophenes (and corresponding dihydro derivatives).

General and Selective Head-to-Head Dimerization of Terminal Alkynes Proceeding via Hydropalladation Pathway

Jahier C., Zatolochnaya O. V., Zvyagintsev N. V., Ananikov V. P., Gevorgyan V., Org. Lett., 2012, 14, 2846-2849.
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A general highly regio- and stereoselective palladium-catalyzed head-to-head dimerization reaction of terminal acetylenes is presented. This methodology allows for the efficient synthesis of a variety of 1,4-enynes as single E stereoisomers. Computational studies reveal that this dimerization reaction proceeds via the hydropalladation pathway.

Unusual Control of Reaction Selectivity via a Subtle Change in the Ligand: Proof of Concept and Application in Pd-Catalyzed C-P Bond Formation

Ananikov V. P., Ivanova J. V., Khemchyan L. L., Beletskaya I. P., Eur. J. Org. Chem., 2012, 3830-3840.
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A new concept for the design of ligands for transition-metal-catalyzed reactions is described. It was shown that the steric effect of triarylphosphanes upon coordination to a metal center can be controlled by switching between unrestricted and restricted rotation modes. The ligands studied were intrinsically tuned to possess characteristic signals in the 1H, 13C, 31P NMR and electrospray ionization mass spectrometry (ESI-MS), thus allowing mechanistic studies to be easily carried out. The efficiency of the developed method was demonstrated in a study on the mechanistic pathways of Pd-catalyzed hydrophosphorylation of alkynes. The catalytic cycle was explored step-by-step by using ESI-MS and NMR methods. Several Pd species were detected under catalytic conditions and the nature of the intermediate metal complexes were evaluated. The process responsible for capturing the Pd catalyst in the inactive resting state and the routes leading to catalyst decomposition were identified and described. For the first time, the catalytic reaction mechanism of hydrophosphorylation of alkynes was revealed at a molecular level, which led to the design of a novel practical procedure for Pd-mediated C–P bond formation. A new Pd/P[(MeO)nC6H5–n]3 catalytic system was proposed with the outstanding ability to control reaction selectivity simply by adjusting the methoxy substituents in the phosphane ligand.

PEG as an Alternative Reaction Medium in Metal-Mediated Transformations

Colacino E., Martinez J., Lamaty F., Patrikeeva L. S., Khemchyan L. L., Ananikov V. P., Coord. Chem. Rev., 2012, 256, 2893-2920.
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Poly(ethylene glycol)s (PEGs) are an interesting environment-friendly alternative to classical solvents. Their combination with metals and metallic salts provides powerful reaction systems for a wide variety of transformations. This study presents an overview of the various reactions developed in PEG together with a metallic species. The influence of PEG on the reaction course, the stabilizing effects of the polymer on the metals and the recycling possibility are reported for the various metallic elements of the periodic table.