Hynek Balcar

Academy of Sciences of the Czech Republic, Praha, Praha, Czech Republic

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Publications (75)182.12 Total impact

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    ABSTRACT: Hoveyda-Grubbs type catalysts with cationic tags on NHC ligands were linker-free immobilized on the surface of lamellar zeolitic supports (MCM-22, MCM-56, MCM-36) and on mesoporous molecular sieves SBA-15. The activity of prepared hybrid catalysts was tested in olefin metathesis reactions: the activity in ring-closing metathesis of citronellene and N,N-diallyltrifluoroacetamide decreased in the order of support MCM-22 ≈ MCM-56 > SBA-15 > MCM-36; the hybrid catalyst based on SBA-15 was found the most active in self-metathesis of methyl oleate. All catalysts were reusable and exhibited low Ru leaching (<1% of Ru content). XPS analysis revealed that during immobilization ion exchange between Hoveyda-Grubbs type catalyst and zeolitic support occurred in the case of Cl(-) counter anion; in contrast, PF6 (-) counter anion underwent partial decomposition.
    Preview · Article · Nov 2015 · Beilstein Journal of Organic Chemistry
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    ABSTRACT: The ligand-exchange reaction between [Ni(PPh3)2Cl2] and (Ph2P)2N(CH2)3Si(OCH3)3 afforded the novel NiII complex [Ni{(Ph2P)2N(CH2)3Si(OCH3)3-P,P′}Cl2] (1) in which the square-planar NiP2Cl2 coordination sphere contains a four-membered Ni–P–N–P ring. Comparison of the structure of 1 and related NiII square-planar or Ni0 tetrahedral complexes containing similar P–N–P ligands shows that the magnitude of the P–Ni–P angle is controlled by the presence of the Ni–P–N–P ring, irrespective of the geometry of the nickel coordination sphere. Direct anchoring of 1 onto SBA-15 molecular sieves through the trimethoxysilyl end-group of the ligand afforded heterogeneous catalyst 1/SBA-15. Both 1 and 1/SBA-15 catalyze Kumada cross-coupling reactions, exhibiting similar activity and a slightly higher product selectivity than the [Ni{Ph2P(CH2)3PPh2-P,P′}Cl2] and [Ni{(Ph2P)2N-(S)-CHMePh-P,P′}X2] (X = Cl, Br) complexes described in the literature. The Grignard reagent employed is likely to induce leaching of the catalyst, which retains its activity in solution.
    Full-text · Article · Jun 2015 · Berichte der deutschen chemischen Gesellschaft
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    ABSTRACT: Chain-growth polymerization of 1,4-diethynylbenzene into conjugated crosslinked polyacetylene-type poly(1,4-diethynylbenzene)s (PDEBs) is reported. While metathesis catalysts (WCl6/Ph4Sn, MoCl5/Ph4Sn, Mo Schrock carbene) fail in this polymerization, insertion Rh catalysts ([Rh(nbd)acac], [Rh(nbd)Cl](2)) provide microporous PDEBs in high yields. The Brunauer-Emmett-Teller (BET) surface, S-BET, of PDEBs prepared with [Rh(nbd)acac] increases, in dependence on the polymerization solvent, in the order: THF << pentane < benzene < methanol < CH2Cl2. S-BET further increases with both increasing monomer concentration and increasing polymerization temperature and reaction time, reaching a highest value of 1469 m(2) g(-1). In addition to micropores, PDEBs contain mesopores. The mesopore volume and average mesopore diameter increase with the time and the temperature of the polymerization up to 2.52 cm(3) g(-1) and 22 nm (72 h, 75 degrees C). The post-polymerization thermal treatment of PDEB (280 degrees C) results in formation of new crosslinks and modification of PDEB texture and sorption behavior manifested mainly by enhancement of H-2 adsorption capacity up to 4.55 mmol g(-1) (77 K, 750 Torr).
    No preview · Article · Oct 2014 · Macromolecular Chemistry and Physics
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    ABSTRACT: Ring-opening metathesis polymerization of vinylnorbornene with molybdenum (VI) complex or with Hoveyda-Grubbs type Ru alkylidene complex provided soluble polymers, poly (VNBE)s of M n about 10 000, having vinyl pendant groups on cyclopentenylenevinylene main chains. Post-polymerization modification via cross-metathesis of pendant vinyl groups with cis-1,4-diacetoxybut-2-ene, 5-hexenyl acetate, allyl acetoacetate, and allyltrimethylsilane was accomplished. Functionalization of poly (VNBE) was also performed via ene-yne cross-metathesis of vinyl pendants with (4-fluorophenyl) acetylene and (2,4-difluorophenyl) acetylene.
    No preview · Article · Sep 2014 · Journal of Polymer Research
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    ABSTRACT: Ruthenium olefin metathesis catalysts bearing a polar quaternary ammonium group in N-heterocyclic ligand were immobilized on silica and siliceous mesoporous molecular sieves with different pore sizes (SBA-15 and MCM-41). The activity of the heterogeneous catalysts was found to increase with an increase in pore size of the support used, with the best results observed for SBA-15-supported catalyst. The influence of reaction conditions (temperature, solvent, catalyst, and substrate concentration) on the efficiency of new heterogeneous catalysts was established. A significant influence of the counterion present in the ruthenium complex on the activity of immobilized catalysts was also found: those derived from chloride containing ion exhibited the highest activity. High activity in ring-closing metathesis of substrates as citronellene, 1,7-octadiene, and diallyl compounds as well as in cross-metathesis of unsaturated aliphatic compounds with methyl acrylate was observed under optimized conditions. In some cases, heterogenization led to catalysts with efficiency higher than those observed for corresponding homogeneous complexes.
    No preview · Article · Aug 2014 · ACS Catalysis
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    ABSTRACT: The Hoveyda-Grubbs type Zhan catalysts (ZC) and Grubbs second generation catalyst (GII) were immobilized on SBA-15 mesoporous molecular sieve by non-covalent interactions and phosphine linkers, respectively. Both hybrid catalysts proved to be highly active and selective in cardanol metathesis and cardanol cross-metathesis with ethene and cis-1,4-diacetoxy-2-butene (DAB). GII/SBA-15 was less active than ZC/SBA-15, however, Ru leaching was significantly lower for GII/SBA-15 (0.5%) than for ZC/SBA-15 (2.5%). In ethenolysis of cardanol, 3-(non-8-enyl)phenol was isolated as a major product. In cross-metathesis with DAB 9-(3-hydroxyphenyl)non-2-enyl acetate and non-2-enyl acetate were formed with high selectivity. Easy catalyst product separation and low Ru leaching provide the products (applicable as detergent precursors and fragrance and flavor agents) free from the catalyst residue.
    No preview · Article · May 2014 · Applied Catalysis A General
  • Hynek Balcar · Wieslaw J. Roth
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    ABSTRACT: A survey of hybrid olefin metathesis catalysts prepared by immobilization of W, Mo, Re, and Ru organometallic complexes on inorganic supports (various kinds of silica and mesoporous molecular sieves) is presented. The main methods for complex immobilization (grafting, anchoring, adsorption, ionic bonding) are described. Selected catalysts are characterized with regard to their activity, transition metal leaching, and reusability. The application of hybrid catalysts in polymerization reaction is discussed. Examples showing the influence of support textural characteristics on catalyst activity and/or selectivity are provided.
    No preview · Chapter · Dec 2013
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    ABSTRACT: Spontaneous catalyst‐free polymerizations of 4‐ethynylpyridine (4EPy) and 2‐ethynylpyridine with bifunctional quaternizing agents (QAs) of bis(bromomethyl)arenes provide highly crosslinked polymer networks in high yields. 13C cross‐polarization magic‐angle spinning (CP/MAS) NMR, Fourier transform IR (FTIR) and diffuse reflectance vis spectroscopy confirm that these networks consist of polyacetylene main chains substituted with pyridyl and pyridiniumyl groups, the latter interconnected with –CH2(arylene)CH2– linkers. Variation of the 4EPy/QA ratio in the polymerization feed results in networks with different extents of crosslinking and pyridyl/pyridin­iumyl ratio (N/N+ from 0 to 1.32). Networks exhibit photolumi­nescence and are also moderately active in CO2 capture (the highest uptake is 16.4 cm3 (STP) g−1 at 293 K and an equilibrium CO2 pressure of 750 Torr).
    No preview · Article · Dec 2013 · Macromolecular Chemistry and Physics
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    ABSTRACT: Complexes [Rh(nbd)(acac)], [Rh(cod)(acac)] and [Rh(cot)(acac)] (nbd = norborna-2,5-diene, cod = cycloocta-1,5-diene, cot = cyclooctatetraene) were investigated as catalysts of polymerization of monosubstituted acetylenes into stereoregular cis-transoid poly(monosubstituted acetylene)s. All complexes (without cocatalyst) are highly active in phenylacetylene (PhA) polymerization in both coordinating (THF) and non-coordinating (CH2Cl2) solvents. [Rh(cot)(acac)] prepared in situ by ligand substitution in [Rh(ethylene)(2)(acac)] with cot is efficient in PhA polymerization even in systems with a high cot content. Selection of solvent and cycloolefin ligand of the catalyst allows the control over poly(phenylacetylene) molecular weight (M-w = 3 x 10(4) to 4 x 10(5)). [Rh(nbd)(acac)] exhibit (moderate) activity also in polymerization of alkylacetylenes (alkyl = n-butyl, tert-butyl, 4-chlorobutyl, cyclopropyl, yields up to 28%, M-w up to 7.3 x 10(4)) and in copolymerization of alkylacetylenes with arylacetylenes. In situ H-1 NMR monitoring of polymerization systems revealed monomer-assisted transformation of [Rh(cycloolefin)(acac)] complexes into precursors of polymerization centres consisting in proton transfer from the monomer to acac ligand of the catalyst under release of acetylacetone. [Rh(cycloolefin)(acac)] catalysts thus differ from the widely used [Rh(nbd)Cl](2) catalyst which is transformed into active centres precursors only in reaction with cocatalyst or a molecule of coordinating solvent and which is efficient only in presence of a proper cocatalyst and/or coordinating solvent. (c) 2013 Elsevier B.V. All rights reserved.
    No preview · Article · Nov 2013 · Journal of Molecular Catalysis A Chemical
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    ABSTRACT: New heterogeneous, reusable catalysts for olefin metathesis have been prepared by immobilizing the Hoveyda-Grubbs first generation type alkylidene (commercially available as the Zhan catalyst-1C) on siliceous mesoporous molecular sieves with different pore sizes and architectures (SBA-15, SBA-16, MCM-41 and MCM-48) having the surface modified with molecules bearing dicyclohexylphosphine (PCy2) end groups. Resulting novel heterogenized catalysts proved high activity in ring-closing metathesis (RCM) of 1,7-octadiene, diethyl diallylmalonate, tert-butyl N,N-diallylcarbamate and N,N-diallyl-2,2,2-trifluoroacetamide, in homometathesis of 1-decene, 5-hexenyl acetate and methyl 10-undecenoate, and in cross-metathesis (CM) of allylbenzene with cis-1,4-diacetoxy-2-butene. The catalytic activity decreased with decreasing pore size of supports in the order SBA-15 > MCM-48 > SBA-16 and MCM-41. Filtration test suggested that the solid catalyst was responsible for the catalytic activity. Catalysts were easily separated from the reaction mixtures and products of low levels of Ru concentration were obtained. (c) 2013 Elsevier B.V. All rights reserved.
    No preview · Article · Nov 2013 · Journal of Molecular Catalysis A Chemical
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    ABSTRACT: Hyperbranched partly cross-linked polycyclotrimers of 1,4-diethynylbenzene, 2,6-diethynylnaphthalene, and 2,6-diethynylanthracene, Pc(1,4-DEB), Pc(2,6-DEN), and Pc(2,6-DEA), respectively, are prepared using TaCl5/Ph4Sn catalyst. Brunauer-Emmett-Teller (BET) surface area, microporosity, and maximum sorption capacity for H-2 and CO2 decrease in the order of decreasing relative content of branching points in polycyclotrimers Pc(1,4-DEB) > Pc(2,6-DEN) > Pc(2,6-DEA), the highest values for Pc(1,4-DEB) being S-BET = 1299 m(2)g(-1),a(H2) = 1.26 wt% (100 kPa, 77 K), and a(CO2) = 10.8 wt% (100 kPa, 273 K). N-2 isotherms show that adsorption/desorption hysteresis occurs already at low equilibrium pressures. CO2 isotherms show that the time allotted to the measurement influences both the maximum adsorption capacity and the hysteresis upon desorption.
    No preview · Article · Sep 2013 · Macromolecular Chemistry and Physics
  • David Bek · Rafał Gawin · Karol Grela · Hynek Balcar
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    ABSTRACT: Ruthenium complex 3b bearing chelating carboxylate ligand was immobilized on mesoporous molecular sieve SBA-15 via cleavage of carboxylate by fluorocarboxylic acid groups introduced on the support surface. The hybrid olefin metathesis catalyst Ru/L/SBA-15, prepared straightforward without use of silver salts, exhibited high activity and selectivity in model metathesis reactions and low ruthenium leaching.
    No preview · Article · May 2012 · Catalysis Communications
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    ABSTRACT: Microporous organic polymers (MOP) of a new type have been synthesised in high yields by a simple coordination polymerization of 1,3-diethynylbenzene, 1,4-diethynylbenzene and 4,4'-diethynylbiphenyl catalysed by [Rh(cod)acac] and [Rh(nbd)acac] complexes. The new MOPs are non-swellable polyacetylene-type conjugated networks consisting of ethynylaryl-substituted polyene main chains that are crosslinked by arylene linkers. Prepared MOP samples have a mole fraction of branching units (by (13) C CP/MAS NMR) from 0.30 to 0.47 and exhibit the BET (Brunaer-Emmett-Teller) surface up to 809 m(2) g(-1) and hydrogen uptake up to 0.69 wt% (77 K, H(2) pressure 750 torr).
    No preview · Article · Jan 2012 · Macromolecular Rapid Communications
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    ABSTRACT: New hybrid olefin metathesis catalysts were prepared by immobilization of Hoveyda–Grubbs type catalyst (commercially available as Zhan catalyst-1B) on the surface of mesoporous molecular sieves differing in pore size and architecture (MCM-41, MCM-48, and SBA-15) and conventional silica for a comparison. The activity of these catalysts was tested in RCM of (−)-β-citronellene, metathesis of 1-decene, ADMET of 1,9-decadiene, and in ROMP of cyclooctene and was found to increase significantly with the increasing pore size of the supports used. In all reactions, the activity of hybrid catalysts based on mesoporous molecular sieves was higher than that of catalyst using conventional silica as a support. In ROMP of cyclooctene, high molecular weight polymer (Mw=300,000) in high yield (70–80%) was obtained with catalysts based on mesoporous supports, however, only 40% polymer yield was obtained using catalyst based on conventional silica.
    No preview · Article · Jan 2012 · Catalysis Today
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    ABSTRACT: Hybrid catalysts for olefin metathesis were prepared by the immobilization of Ru alkylidenes (Grubbs catalysts) on mesoporous molecular sieves SBA-15 and MCM-41 having the surface modified with molecules bearing dicyclohexylphosphine (PCy2) and pyridine end groups. Hybrid catalysts with Ru attached to the surface via PCy2 ligands exhibited higher activity and stability than those with Ru attached via pyridine ligands. The former catalysts exhibited a high activity in a series of metathesis reactions (RCM, ROMP, and cross-metathesis) reaching turnover numbers (TONs) from 200 to 2000 and being reusable several times. The filtration tests for all catalysts suggested that the solid catalysts were responsible for catalytic activity during the reactions. Only low Ru leaching was observed. A positive effect of the pore size of the support on catalyst activity was observed for the metathesis of methyl oleate.
    No preview · Article · May 2011 · ACS Catalysis
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    ABSTRACT: Substituted polyvinylenes, polymers with conjugated polyene main chains, attract attention because of their unique properties implicating applications in electronics and optics [1] (electro- and photoconductivity, electro- and photoluminescence, optic non-linearity). So far, these polymers have been prepared almost exclusively by homogeneously catalyzed polymerization of corresponding substituted acetylenes with transition metal catalysts (most frequently compounds of W, Mo, Rh and Pd) [2–4]. However, catalyst residues in polymers may undesirably affect the polymer properties (especially those essential for their applications) and polymer purification (e.g. by repeated polymer precipitation) leads often to the decrease of molecular weight and changes in microstructure resulting from polymer degradation [5,6]. Therefore, new polymerization procedures minimizing the content of catalyst residues in the resulting polymers can be of important advantage.
    No preview · Chapter · Mar 2011
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    ABSTRACT: A commercially available Hoveyda-Grubbs type catalyst (RC303 Zhannan Pharma) was immobilized on mesoporous molecular sieves MCM-41 and on SBA-15 by direct interaction with the sieve wall surface. The immobilized catalysts exhibited high activity and nearly 100% selectivity in several types of alkene metathesis reactions. Ru leaching was found to depend on the substrate and solvent used (the lowest leaching was found for ring-closing metathesis of 1,7-octadiene in cyclohexane - 0.04% of catalyst Ru content). Results of XPS, UV-vis and NMR spectroscopy showed that at least 76% of the Ru content was bound to the support surface non-covalently and could be removed from the catalyst by washing with THF.
    Full-text · Article · Jan 2011 · Beilstein Journal of Organic Chemistry
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    ABSTRACT: New heterogeneous catalysts for ring opening metathesis polymerization (ROMP) have been prepared by immobilization of RuCl2(p-cymene)(PCy3) (Cy=cyclohexyl) on silica and siliceous mesoporous molecular sieves SBA-15 and MCM-41. Activity of these catalysts was investigated in ROMP of norbornene (NBE) and its derivatives (dicyclopentadiene, 5-norbornene-2-yl acetate). High molecular weight polymers (Mw up to 400000) were prepared in yields up to 80% using catalysts based on mesoporous sieves. In contrast, with catalyst based on conventional silica the yield did not exceed 28% (ROMP of NBE). Filtration test proved that the catalytic activity was bound to the solid phase. Catalysts could be easily separated from the reaction mixture in contrast to the corresponding homogeneous system. Therefore, polymers with reduced amounts of catalyst residues were obtained.
    No preview · Article · Nov 2010 · Journal of Molecular Catalysis A Chemical
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    No preview · Article · Jul 2010 · ChemInform
  • Hynek Balcar · Jiří Čejka
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    ABSTRACT: Siliceous mesoporous molecular sieves MCM-41, MCM-48 and SBA-15 and organised mesoporous alumina represent progressive supports for new heterogeneous catalysts for olefin metathesis and metathesis polymerization. In combination with Mo and Re oxides they provide catalysts of considerably higher activity in comparison with those based on conventional silica and alumina. Immobilization of Mo and Ru alkylidenes on these materials led to the highly active and selective catalysts with negligible leaching of transition metal.
    No preview · Article · Jul 2010 · Macromolecular Symposia