Andrey F. Asachenko

Expanded‐Ring N‐Heterocyclic Carbenes Efficiently Stabilize Gold(I) Cations, Leading to High Activity in π‐Acid‐Catalyzed Cyclizations

A series of six- and seven-membered expanded-ring N-heterocyclic carbene (er-NHC) gold(I) complexes has been synthesized using different synthetic approaches. Complexes with weakly coordinating anions [(er-NHC)AuX] (X(-) = BF4(-), NTf2(-), OTf(-)) were generated in solution. According to their (13)C NMR spectra, the ionic character of the complexes increases in the order X(-) = Cl(-) < NTf2(-) < OTf(-) < BF4(-). Additional factors for stabilization of the cationic complexes are expansion of the NHC ring and the attachment of bulky substituents at the nitrogen atoms. These er-NHCs are bulkier ligands and stronger electron donors than conventional NHCs as well as phosphines and sulfides and provide more stabilization of [(L)Au(+)] cations. A comparative study has been carried out of the catalytic activities of five-, six-, and seven-membered carbene complexes [(NHC)AuX], [(Ph3 P)AuX], [(Me2S)AuX], and inorganic compounds of gold in model reactions of indole and benzofuran synthesis. It was found that increased ionic character of the complexes was correlated with increased catalytic activity in the cyclization reactions. As a result, we developed an unprecedentedly active monoligand cationic [(THD-Dipp)Au]BF4 (1,3-bis(2,6-diisopropylphenyl)-3,4,5,6-tetrahydrodiazepin-2-ylidene gold(I) tetrafluoroborate) catalyst bearing seven-membered-ring carbene and bulky Dipp substituents. Quantitative yields of cyclized products were attained in several minutes at room temperature at 1 mol % catalyst loadings. The experimental observations were rationalized and fully supported by DFT calculations.

Catalytic activity of palladium complexes with stable diaminocarbenes containing five-, six- and seven-membered rings in the Suzuki-Miyaura reaction

A comparative study of catalytic activity of palladium complexes with N-heterocyclic carbenes in the Suzuki-Miyaura reaction was conducted. The studies were carried out for the complexes containing carbenes with five-membered rings based on imidazole and imidazoline, and carbenes with expanded six- and seven-membered rings. The influence of the solvent nature, the base type, and the iodide ions on the catalytic activity of complexes was also examined.

Addition homo- and copolymerization of 3-triethoxysilyltricyclo[4.2.1.0 2,5 ]non-7-ene

New norbornene type monomer bearing reactive triethoxysilyl group was synthesized, and its addition homo- and copolymerization with 3-trimethylsilyltricyclonon-7-ene was studied. The target monomer was obtained using regio- and stereospecific [2σ+2σ+2π] cyclo-addition of quadricyclane with vinyltrichlorosilane followed by the reaction of the formed cycloadduct with ethanol in the presence of triethylamine. Addition polymerization was investigated over the three-component Pd-containing catalytic system (Pd complex, Na+[B(3,5-(CF3)2C6H3)4]–(cocatalyst) and tricyclohexylphosphine). The N-heterocyclic carbene Pd complex (SIPrPd(cinn)Cl) with high activity and tolerance to the Si—O—C moieties was used as a catalyst. The yields of the homo- and copolymers were 24—68% depending on the monomer (comonomer): Pd: B: PCy3 ratio. The obtained addition polymers are high-molecular-weight amorphous products, the glass transition temperature of which exceeds 300 °C. The presence of reactive Si(OC2H5)3 groups in the homo- and copolymers made it possible to carry out a hard-to-realize cross-linking involving side substituents and followed by the formation of insoluble polymers.

An unprecedentedly simple method of synthesis of aryl azides and 3-hydroxytriazenes

Fischers approach towards the synthesis of aryl azides and triazinoles from diazonium salts and hydroxylammonium chloride (phenylhydraxylamine) was reinvestigated and optimized. The new methodology enables the preparation of aryl azides and triazinoles in high yields in water at room temperature. The procedure is very simple, robust, easily scalable, reproducible, and “green”.

Janus tricyclononene polymers bearing tri(n-alkoxy)silyl side groups for membrane gas separation

A series of polymers of a new type, which contain rigid polymer main chains (glassy nature) and long flexible side substituents (rubbery nature), were prepared from norbornene derivatives with (AlkO)3Si-groups of a different length (Alk = Me, Et, n-Pr, n-Bu) as promising materials for membrane separation of gaseous hydrocarbons. The 1st generation Grubbs complex and Pd–N-heterocyclic carbene complex in combination with Na+[(3,5-(CF3)2C6H3)4B]− and PCy3 were used as catalysts of metathesis and addition polymerization in the synthesis of high-molecular weight polymers (Mw ≤ 1.1 × 106) with good or high yields (up to 99%). The prepared addition polymers were glassy, while the glass transition temperature of metathesis polymers depended on the length of the alkyl-group in (AlkO)3Si-substituents and it varied in the range of −44 to 61 °C. The dramatic tuning of polymer gas-transport properties was demonstrated by the change of the polymer main chain structure and the length of tri(n-alkoxy)silyl side groups. For example, we have succeeded for the first time in obtaining metathesis polynorbornenes, which turned out to be more permeable than their addition isomers. Not being large free volume polymers, all studied metathesis and addition polytricyclononenes exhibited solubility controlled permeation of hydrocarbons (P(n-C4H10) up to 8100 barrer) and high C4/C1 selectivity (22–49).

Fluorinated Unsymmetrical N,N'-Diaryl Imidazolium Salts-New Functionalized NHC-Ligand Precursors

An efficient and scaled-up synthesis of the imidazol-2-ylidene-based unsymmetrical NHC precursors bearing the sterically demanding hexafluoroisopropylalkoxy group [(CF3 )2 (OR)C-] at the ortho position of the N-aryl substituent was developed. The key step of the method involved the transformation of a Mes-substituted oxazolinium tetrafluoroborate salt through the reaction with the corresponding binucleophilic fluoroalkyl-substituted aniline. The subsequent post-modification of the resulting hydroxyl-containing salt through a simple one-step O-alkylation protocol provided access to a new family of unsymmetrical fluorinated NHC precursors. These compounds were successfully utilized for the preparation of several novel metal complexes. The molecular structures of some NHC precursors and their metal complexes have been unambiguously characterized by single-crystal X-ray diffraction analysis. A preliminary evaluation of the catalytic activity of the palladium complexes was performed on a Buchwald-Hartwig amination reaction. As a result, two PEPPSI-type (PEPPSI=pyridine-enhanced pre-catalyst preparation stabilization and initiation) Pd complexes have demonstrated promising activity in alkane solvents.

Synthesis and properties of polynorbornenes containing trialkoxysilyl groups

In this work we report the synthesis and polymerization of new norbornenes containing trialkoxysilyl groups. These monomers were reactive both in ROMP and in addition polymerization. Obtained polymers possessed interesting properties. So despite of low surface area they were good permeable, and some of them exhibited a low tendency to aging. The solubility controlled selectivity for hydrocarbons was observed. These properties would allow finding industrial application of obtained polymers for the membrane gas separation of hydrocarbon mixtures.In this work we report the synthesis and polymerization of new norbornenes containing trialkoxysilyl groups. These monomers were reactive both in ROMP and in addition polymerization. Obtained polymers possessed interesting properties. So despite of low surface area they were good permeable, and some of them exhibited a low tendency to aging. The solubility controlled selectivity for hydrocarbons was observed. These properties would allow finding industrial application of obtained polymers for the membrane gas separation of hydrocarbon mixtures.

Addition polymerization of 5-vinyl-2-norbornene and 5-ethylidene-2-norbornene

Herein we described addition polymerization of 5-ethylidene-2-norbornene and 5-vinyl-2-norbornene in the presence of N-heterocyclic carbene Pd-complexes. After activation with B- or/and Al-organic compounds, these complexes were found to be selective and highly active catalysts for polymerization of these bifunctional norbornenes. The studied catalytic systems were active even at very high monomer/Pd ratios (up to 250 000/1) and their catalytic activity was in the range of 5·106-3·107 gpolymer/(molPd·h). Some interesting relationships between the structure of Pd-complexes and the catalyst activity in polymerization were found. In the presence of these complexes, amorphous, glassy and soluble polynorbronenes containing side alkenyl groups were prepared and characterized by means of IR and NMR spectroscopy.Herein we described addition polymerization of 5-ethylidene-2-norbornene and 5-vinyl-2-norbornene in the presence of N-heterocyclic carbene Pd-complexes. After activation with B- or/and Al-organic compounds, these complexes were found to be selective and highly active catalysts for polymerization of these bifunctional norbornenes. The studied catalytic systems were active even at very high monomer/Pd ratios (up to 250 000/1) and their catalytic activity was in the range of 5·106-3·107 gpolymer/(molPd·h). Some interesting relationships between the structure of Pd-complexes and the catalyst activity in polymerization were found. In the presence of these complexes, amorphous, glassy and soluble polynorbronenes containing side alkenyl groups were prepared and characterized by means of IR and NMR spectroscopy.

Distribution of benzo-substituted crown-ethers between chloroform and water: effects of macrocycle ring size and lithium chloride

AbstractSmall size benzo-substituted crown ethers are attractive complexing agents for lithium isotope separation by solvent extraction. Low transfer of the crown ethers from solvent to water is a key point for applicability of the extractants. In the present study, 9- and 12-membered crown ethers were synthesized, and their distribution between chloroform and water was studied. Polyether ring size, benzene substituents and addition of LiCl to water were found to effect on distribution constants. Low losses of the macrocycles were observed at single-stage contact with aqueous phase. However, these losses should be taken into account in the design of multistage processes for the preparation of highly enriched lithium isotopes.

Addition Polymerization of 5-Ethylidene-2-Norbornene in the Presence of Pd N-Heterocyclic Carbene Complexes

New high-performance catalytic systems based on Pd N-heterocyclic carbene complexes for the selective addition polymerization of 5-ethylidene-2-norbornene (ENB) were proposed. With these catalysts, polymerization can be conducted at unprecedentedly high monomer/catalyst ratio (up to 5 × 105/1) and gives high-molecular-weight soluble polymers with good film-forming properties. Varying the polymerization conditions (reaction temperature, monomer and catalyst concentrations, monomer/Pd ratio) makes it possible to prepare soluble ENB-based addition polymers with specified molecular weights in reasonable yields.