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A pH-responsive mesalazine–crown ether and perfluoro tert-butyl functionalized polynorbornene supramolecular assembly (smc-1-4-cp-1-5) has been prepared. A promoted mesalazine (1) anti-inflammatory drug sustained release has been observed at elevated pH (7–9) enabling targeted topical and sustained drug dosing in the inflamed lower gastrointestinal (GI) tract. Thermoanalytical and solid-state NMR investigations of the supramolecular assembly revealed an amorphous, solid solvent structure showing that 1 is evenly distributed in the supramolecular polymer framework. In situ1H NMR investigation revealed a downshift of the respective hydrogens upon mesalazine–supramolecular polymer assembly formation. The equilibrium constant of the complex of crown ether-functionalized norbornene monomer (5) and 1 (log K = 3.4 ± 0.5, in a DMSO-d6–CD2Cl2 1 : 1 mixture) was calculated.

Conversion of 1-hexene or olefins obtained by fluid catalytic cracking (FCC) to propylene via isomerization–metathesis (ISOMET) was investigated using ethylene as a cross-coupling agent. Zeolite H-beta (HBEA) was applied as an isomerization catalyst. The olefin metathesis (OM) catalysts were about 12 wt% molybdena, supported on zeolite beta (MoO3/HBEA), and γ-alumina (MoO3/Al2O3). HBEA-supported catalyst with a lower molybdena content (6 wt%) was also investigated. The catalysts were characterized by X-ray diffractometry (XRD), H2-temperature-programmed reduction (H2-TPR), and Fourier transform infrared (FT-IR), visible Raman, in situ ultraviolet-visible (UV/VIS) and XPS spectroscopy. It was shown that HBEA is a highly active and robust catalyst of double-bond isomerization. Applying a physical mixture of HBEA and 12MoO3/Al2O3 catalyst at 150 °C and 3 bar ethylene pressure, 60% conversion of 1-hexene to propylene was attained. Interestingly, quantitative conversion to propylene was achieved after reactivation of the deactivated catalyst in an argon atmosphere at 550 °C. It was found that the pre-treatment of the catalyst with olefins such as ethylene before inert gas activation resulted in significant catalyst activity improvement. This suggests that the adsorbed olefins may play a key role in the formation of active metal centers during the catalyst reactivation process. The catalyst mixture also had good performance in the conversion of FCC olefins to propylene. The MoO3/HBEA catalysts have rendered reasonable activity; however, the catalysts showed a significantly shorter lifetime than the alumina-containing catalyst mixture.

Ammonia borane (AB) has received extensive attention in recent years as an emerging hydrogen storage material due to its high hydrogen density (19.6 wt %), nontoxicity, stability, and water solubil...

Cyclic polymers are topologically interesting and envisioned as a lubricant material. However, scalable synthesis of pure cyclic polymers remains elusive. The most straightforward way is to recycle a used catalyst for the synthesis of cyclic polymers. Unfortunately, it is demanding because of the catalyst’s vulnerability and inseparability from polymers, which depreciates the practicality of the process. Here, we develop a continuous process streamlined in a circular way that polymerization, polymer separation, and catalyst recovery happen in situ, to dispense a pure cyclic polymer after bulk ring-expansion metathesis polymerization of cyclopentene. It is enabled by introducing silica-supported ruthenium catalysts and a newly-designed glassware. Also, different depolymerization kinetics of the cyclic polymer from its linear analogue is discussed. This process minimizes manual labor, maximizes security of vulnerable catalysts, and guarantees purity of cyclic polymers, thereby showcasing a prototype of a scalable access to cyclic polymers with increased reusability of precious catalysts (≥415,000 turnovers).

Vinyl alcohol (VA) copolymers having fine tunable polarities are emerging materials in drug delivery applications. VA copolymers rendering well-defined molecular architecture (C/OH ratio = 2, 4, 5 and 8) were used as carriers for model drug compound, fluorescein, which exhibited significantly different release characteristics depending on the polarity of the polymers. Based on the preliminary drug release tests the well-defined VA copolymer having C/OH = 5 ratio, poly(vinyl alcohol alt-propenylene) copolymer (PVA-5) was selected for nanocomposite synthesis. Sorafenib anticancer drug was embedded into PVA-5 (C/OH = 5 ratio) nanoparticles by nanoprecipitation resulting in nanoparticles exhibiting unusual cubic shape . The sorafenib-loaded nanocomposites showed continuous release during a day and concentration-dependant cytotoxicity on HT-29 cancer cells. This might be interpreted by the sustained release of the drug.

Solvent-free hydroconversion of levulinic acid (LA) was studied over Co/silica catalysts by applying a flow-through fixed-bed microreactor. Consecutive hydrogenation/hydrogenolysis and dehydration reactions proceeded over the catalyst having Co0 metal and CoOx Lewis acid active sites. As a first step, LA was dehydrated to form an angelica lactone (AL) intermediate. Because dehydration of LA is a facile reaction, the selectivity was controlled by the hydrogenation/hydrogenolysis activity of the catalyst. At 200 °C and 30 bar total pressure in the steady state, the catalyst could only saturate the double bond of the AL ring. Thus, γ-valerolactone (GVL) was obtained with 98 mol% yield at full LA conversion. However, at temperatures ≥225 °C, the hydrogenation activity was high enough to cleave the GVL ring and obtain 2-methyltetrahydrofuran (2-MTHF) with a stable yield of about 70 mol%. FT-IR spectroscopic examination of the adsorbed LA showed the formation of H-bound LA and also surface carboxylate. 4-Hydroxy-3-pentenoate and 4-hydroxypentanoate were substantiated as surface intermediates of lactone formation by dehydration.

Copolymers containing hydroxyl (i.e. vinyl alcohol, VA) or fluorine functionalities are synthetic macromolecules having prominent biomedical applications. The concentration of hydroxyl groups along the polymer chain controls the polymer polarity. Moreover, the introduction of perfluorinated organic moieties via the OH functionalities may lead to macromolecules having potential magnetic resonance imaging (MRI) active properties. The ring-opening metathesis polymerization (ROMP) reaction using well-defined ruthenium-catalyzed systems is one of the most promising synthetic tools to fabricate such polymers. Co-polymerization of norbornene grafted pyridino-18-crown-6 ether (7) with fluorine-functionalized norbornenes (10 and 11) results in polymers bearing host molecular moieties. It has been demonstrated that the complexation of these host copolymers with biogenic amines including dopamine hydrochloride (12) and L-alanyl-L-lysine dipeptide hydrochloride (13) is straightforward. Based on the 1H NMR investigation of the 7 and 12 complexation, an equilibrium constant of log K = 4.3 ± 0.6 could be calculated. The in situ1H NMR investigations have revealed that the complex formation of 13 with monomer 7 and perfluorinated copolymer cp-7-10 takes place via both the lysine –NH3+ and the alanine –NH3+ moieties. However, in the case of homopolymer poly-7, the lysine–NH3+ group coordination was observed exclusively. According to theoretical calculations, molecular switching of the crown ether structure of both the 7 monomer and its cp-7-10 copolymer were observed from 90 degrees bent to planar structure upon –NH3+ ion coordination.

Semiochemicals are substances or mixtures that carry messages and are used for communication between individuals of the same or different species. Semiochemicals that are used in pest control are called biopesticides. Conventional pesticides, which are generally synthetically derived and unnatural, inactivate or kill the pests, whereas biopesticides are naturally occurring compounds that attract insects to a trap or interfere with their reproduction. There are several advantages to biopesticides. Compared with conventional pesticides, biochemical-based pesticides are often less toxic and therefore have a significantly lower impact on human health and the environment. Moreover, biopesticides are pest-selective and as such do not negatively impact other organisms such as insects, mammals, or birds. Other advantages of biopesticides include high potency, meaning that smaller amounts of biopesticide are required, less resistance by target organisms, and the ability to biodegrade more quickly than conventional...

Cross metatheses of tung oil, a nonedible vegetable oil and α-eleostearic acid ((9Z,11E,13E)-octadeca-9,11,13-trienoic acid, ESA) methyl ester (1), obtained from tung oil containing the same highly unsaturated, conjugated double bonds, have been carried out with cis-1,4-diacetoxy-2-butene (2) using Hoveyda-Grubbs (3-HG2) or Grubbs second or third generation catalysts (3-G2 or 3-G3). The reactions followed by Pd/C-catalyzed hydrogenation give methyl 11-acetoxyundecanoate (4) as a polyester raw material, 1,6-diacetoxy-hexane (5) as a precursor of 1,6-hexanediol (6) polyurethane monomer, and heptyl acetate as a fragrance (7) in 53–99% yields after Pd/C-catalyzed hydrogenation. The one-pot isomerization metathesis of α-linolenic acid ((9Z,12Z,15Z)-9,12,15-octadecatrienoic acid, ALA) methyl ester (7) using 2 as cross coupling agent, RuHCl(CO)(PPh3)3 (9) as isomerization, and 3-G2 as a metathesis catalyst followed by Pd/C catalyzed hydrogenation leads also to the formation of 5 and the homologues of 4 and 7 in ...

Cross-metathesis (CM) of conjugated polyenes, such as 1,6-diphenyl-1,3,5-hexatriene ( 1 ) and α-eleostearic acid methyl ester ( 2 ) with several olefins, including 1-hexene, dimethyl maleate and cis -stilbene as model compounds has been carried out using (1,3-bis-(2,4,6-trimethylphenyl)-2-imidazolidinylidene)-dichloro( o -isopropoxyphenylmethylene)ruthenium (Hoveyda-Grubbs 2nd generation, HG2 ) catalyst. The feasibility of these reactions is demonstrated by the observed high conversions and reasonable yields. Thus, regardless of the relatively low electron density, =CH–CH= conjugated units of molecules, including compound 2 as a sustainable, non-foodstuff source, can be utilized as building blocks for the synthesis of various value-added chemicals via olefin metathesis. DFT-studies and the product spectrum of the self-metathesis of 1,6-diphenyl-1,3,5-hexatriene suggest that a Ru η 1 -allylidene complex is the active species in the reaction.

Ring opening metathesis polymerization (ROMP) of a series of low-strain cyclic olefins and their hydroxyl derivatives using second generation Hoveyda–Grubbs catalyst has been investigated. Additionally, density functional theory (DFT) calculations were performed to evaluate the ring strain energies of the cyclic olefins and their hydroxyl derivatives, coupled with kinetic studies for the ROMP reactions. It was found that among different ring size monomers, Cy8 having a relatively moderate ring strain energy in comparison with the other cyclic olefins, exhibited the highest monomer conversion. The effect of temperature (0, 10, 15, and 25 °C) and monomer concentration (1 M; 2.5 M and 5 M for Cy5; and 1 M and 5 M for Cy7) for the cyclic olefins Cy5 and Cy7 were investigated. In general, the experimental results for the kinetic ROMP studies obtained using complex HG2 correlate really well with the DFT calculations determined for the ring strain energies of the cyclic olefins. For comparison, DFT calculations predicted the following trend for the ring strain energies Cy8 > Cy5 > Cy7 > Cy6, and the polymerizations carried out experimentally followed the same trend in terms of monomer conversion, with the exception of Cy5 and Cy7 at lower concentrations, which followed this trend Cy8 > Cy7 > Cy5 > Cy6. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3137–3145

Ruthenium catalyzed ring closing metathesis (RCM) and ring opening metathesis polymerization (ROMP) reactions using a supported bis(arylimino)acenaphthene N-heterocyclic carbene (BIAN-NHC) complex have been reported. The BIAN-NHC Ru-complex exhibits excellent catalytic activity and tolerates a wide range of substrates at low catalyst loadings. DFT calculations were also carried out on some selected key intermediates in the reaction mechanism to study the effect of having the conjugated aromatic moiety (BIAN-NHC) in the backbone of the complex. The newly synthesized BIAN-NHC Ru-complex shows comparable catalytic activities to the commercially available second generation Ru catalyst HG2. The recycled complex was reused for up to eight reaction cycles for the RCM of N,N-diallyl tosylamine affording a high average isolated yield, with lower levels of Ru contamination in the final product.

Linear trans-polypentenamers are highly desired materials among synthetic tire additives due to their comparable physical properties to natural rubber. trans-Polypentenamer can be prepared by equilibrium ring-opening metathesis polymerization (ROMP) using well-defined ruthenium catalyst systems. This unique feature of the equilibrium polymerization reaction opens a way for the synthesis of durable, environmentally benign elastomers where polymers including synthetic tire additives can be synthesized and readily recycled using the same transition metal catalyst system. The addition of silica fillers significantly improves the physical properties of the composite materials in comparison to the use of polymeric material. It is also known that the structural effects and the polymer–filler surface interaction are of prime importance. Herein, we report on the synthesis of silica filler compatible recyclable polypentenamer copolymers via equilibrium ROMP of cyclopentene 1 and 4-(triethoxy)siloxy cyclopentene 11....

In the past decade, numerous examples of chemical technologies based on olefin metathesis have been developed to make olefin metathesis increasingly dominant in several sustainable and green chemical processes. In spite of the wide application profile, conjugated olefin metathesis, especially conjugated polyene metathesis, is an area of great interest with little exploration. The metathesis of conjugated polyenes is often cumbersome and requires a high catalyst loading, most probably because of the formation of poorly active or inactive ruthenium η3-vinylcarbene intermediates. A mechanistic understanding and the development of a new highly active catalytic system for olefin metathesis will open new areas for exploration, such as the utilisation of cyclopentadiene and other petrochemical by-products or a new way to use butadiene, isoprene and conjugated electron systems that contain natural products such as terpenes and polyunsaturated fatty acids. An understanding of the mechanism of ruthenium η1–η3-vinylcarbene interconversion may open the way to the development of a new generation of Ru-based latent metathesis catalyst systems. This review summarises the most relevant pioneering work focused on the metathesis of conjugated polyenes to open new ideas for the development of forthcoming latent metathesis catalysts and to explore different applications.

Equilibrium ring-opening metathesis polymerization (ROMP) of cyclic olefins using a soluble supported second-generation Ru complex has been investigated. Cycloolefin homo- and copolymers are of great academic and industrial importance owing to their interesting applications as packaging materials, adhesives in coatings, and optoelectronics. The supported complex exhibits good chemical stability and was effective in ROMP of strained cyclic olefins. In addition, the complex is easily phase separated from the product, resulting in lower residual ruthenium in the final polymer product compared with the homogeneous complex.

With metal-based catalysts, it is quite common that a ligand (L) must first dissociate from a catalyst precursor (L'n M-L) to activate the catalyst. The resulting coordinatively unsaturated active species (L'n M) can either back react with the ligand in a k-1 step, or combine with the substrate in a k2 step. When dissociation is not rate determining and k-1 [L] is greater than or comparable to k2 [substrate], this slows the rate of reaction. By introducing a phase label onto the ligand L and providing a suitable orthogonal liquid or solid phase, dramatic rate accelerations can be achieved. This phenomenon is termed "phase-transfer activation". In this Concept, some historical antecedents are reviewed, followed by successful applications involving fluorous/organic and aqueous/organic liquid/liquid biphasic catalysis, and liquid/solid biphasic catalysis. Variants that include a chemical trap for the phase-labeled ligands are also described.

Polymers exhibiting cyclic topology have attracted great interest over the past 30 years. Macrocycles or cyclopolymers with more than 20 repeating monomer units are considered exceptional candidates for thermoplastic engineering application due to unique properties in comparison to their linear analogues including large hydrodynamic radii and functional group density, heat resistance, good insulating ability and low intrinsic viscosity. Cyclic polymers are thus expected to exhibit improved physical and mechanical properties for certain applications due to the absence of end groups. Although synthetic challenges have historically limited research on cyclic polymers, recent developments in ruthenium catalyzed ring-expansion metathesis polymerization (REMP) have enabled the synthesis and the preliminary investigation of structure-property relationships of high molecular weight macrocycles. In REMP reactions the polymer formation is proposed to proceed through a transient macrocyclic complex in which both ends of the growing polymer chain remain attached to the Ru center. This article summarizes the recent discoveries on the field of REMP assisted cyclopolymer based material development.

In the past decade, numerous examples of chemical technologies based on olefin metathesis have been developed to make olefin metathesis increasingly dominant in several sustainable and green chemical processes. In spite of the wide application profile, conjugated olefin metathesis, especially conjugated polyene metathesis, is an area of great interest with little exploration. The metathesis of conjugated polyenes is often cumbersome and requires a high catalyst loading, most probably because of the formation of poorly active or inactive ruthenium η3-vinylcarbene intermediates. A mechanistic understanding and the development of a new highly active catalytic system for olefin metathesis will open new areas for exploration, such as the utilisation of cyclopentadiene and other petrochemical by-products or a new way to use butadiene, isoprene and conjugated electron systems that contain natural products such as terpenes and polyunsaturated fatty acids. An understanding of the mechanism of ruthenium η1–η3-vinylcarbene interconversion may open the way to the development of a new generation of Ru-based latent metathesis catalyst systems. This review summarises the most relevant pioneering work focused on the metathesis of conjugated polyenes to open new ideas for the development of forthcoming latent metathesis catalysts and to explore different applications.

Review: [historical antecedents and applications involving fluorous/organic and aqueous/organic liquid/liquid biphasic catalysis, and liquid/solid biphasic catalysis; 56 refs.

N-Heterocyclic Carbenes (NHCs): Over the last two decades N-Heterocyclic carbenes (NHCs) have immensely attracted chemists in nearly all fields of chemistry. N-Heterocyclic carbenes are commonly encountered in coordination chemistry, they are extensively used as ligands for organometallic complexes. Perhaps the biggest hit of NHCs ligands was their use in Grubbs II catalyst for olefin metathesis chemistry. It is noteworthy that the success of NHCs ligands in catalysis is due to several factors favoring their high activity, selectivity and stability when compared to the phosphine counterparts in Grubbs I catalyst [1]. Supported Catalysts: Increased environmental and health awareness requires that designing new metal-catalysts should focus not only on increasing activity and selectivity but also on finding new strategies that help chemists recycle and separate the metal-catalyst from the reaction mixture. In general, homogenous catalysis is preferred over heterogeneous catalysis. This is due to the higher turnover number, better selectivity and usually lower operating temperatures required. On the other hand, heterogeneous catalysis has the advantage of the ease of separation of the catalyst from the final products and is generally less expensive. One important strategy is to use catalysts attached to a heterogeneous support and separate them from the products by simple filtration. Alternatively, homogeneous catalysts that can self-separate from the products by selective solvent extraction would be of great interest. The frequency of their reuse would be environmentally beneficial and to a higher extent this should overcome the lower activity of conventional heterogeneous catalysts. Metal catalysts that can self-separate from the reaction mixture are of great importance due to the reduced metal leaching into the product mixture. In addition, their reuse and recovery make this overall process much greener compared to the conventional homogeneous/heterogeneous catalysis systems. Ever since Herrmann et al. [2] reported the polystyrene supported NHC-palladium catalyst, studies have largely been focused on the use of polymeric supports for NHC-palladium catalysts. While polyethylene-glycol-supported catalyst can be extracted with a polar solvent, Bergbreiter et al. [3] and others have showed that polyisobutylene (PIB) is a useful support for ligands and their metal catalysts (Pd, Ru…) having preferable solubility towards solvents with low polarities such as hexanes, heptanes and decanes. In all of these biphasic systems for cross-coupling/olefin metathesis, the design is mainly focused on the recovery and the reuse of the supported catalysts. Biphasic catalysis having thermomorphic behavior have witnessed great developments due to their temperature-dependent miscibility [4]. While reactions in these biphasic mixtures can be conducted under homogeneous conditions at high-temperatures, the supported catalysts and the products/by-products can be efficiently separated by restoring the biphasic conditions at a low-temperature (Scheme 1). Herein we report the synthesis of new PIB-supported N-heterocyclic carbenes ligands having two different frameworks and their Pd-complexes, 1 and 2. The use, recovery and effectiveness of catalysts are detailed in both Heck and Suzuki cross-coupling reactions (Scheme 2). Metal leaching to the polar phase will be discussed too. Scheme 2: Heck cross-coupling and Suzuki cross-coupling using catalysts 1 and 2.References:[1] Scholl, M.; Ding, S.; Woo-Lee, C.; Grubbs, R. H. Org. Lett. 1999, 1, 953.[2] Schwarz, J.; Böhn, V. P. W.; Gardiner, M. G.; Grosche, M.; Herrmann, W. A.; Hieringer, W.; Raudaschl-Sieber, G. Chem. Eur. J. 2000, 6, 1773–1780.[3] (a) Bergbreiter, D. E.; Su, H-L.; Koizumi, H.; Tian, J. J. Organomet. Chem, 2011, 696, 1272. (b) Bergbreiter, D. E.; Tian, J. Tetrahedron Lett. 2007, 48, 4499–4503.[4] J. A. Gladysz, Dr. C. Rocaboy Chem. Eur. J. 2003, 9, 88. (b) Al-Hashimi, M.; Hongfa, C.; George, B.; Bazzi, H.S.; Bergbreiter, D. E. J. Polym Sci Part A: Polym. Chem., 2012, 50, 3954. (c) Al-Hashimi, M.; Abu Bakar, M.D.; Elsaid, K.; Bergbreiter, D. E.; Bazzi, H.S. RSC Advances, 2014, 4, 43766.

Grubbs’ second-generation alkene metathesis catalyst and the fluorous analog (H2IMes)((Rf8(CH2)2)3P)(Cl)2Ru(═CHPh) (1; H2IMes/Rf8 = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene/(CF2)7CF3) catalyze ring-opening metathesis polymerizations of norbornene at essentially identical rates (CDCl3, RT). However, dramatic accelerations can be observed with 1 in the presence of the fluorous solvent perfluoro(methylcyclohexane) (PFMC). The fluorous phosphine (Rf8(CH2)2)3P must first dissociate from 1 to generate the 14-valence-electron intermediate that begins the catalytic cycle and should be scavenged by the PFMC phase (PFMC/toluene partition coefficient >99.7

High-pressure in situ IR and NMR investigations of the hydromethoxycarbonylation of 1,3-butadiene (1) to methyl 3-pentenoate (2) in methanol in the presence of Co2(CO)8 and pyridine under carbon monoxide has revealed that the reaction starts by the methanol- and/or pyridine-assisted disproportionation of Co2(CO)8, followed by the establishment of equilibria involving the ionic species [Co(Py)6]2+{[Co(CO)4]−}2, [Co(Py)6]2+[MeO]−[Co(CO)4]−, [PyH]+[Co(CO)4]−, and [MeOH2]+[Co(CO)4]−. The addition of HCo(CO)4 (3) to pyridine or methanol results in the formation of [PyH]+[Co(CO)4]− and [MeOH2]+[Co(CO)4]−, respectively, and 3 is not detectable by either IR or NMR. The ionic 1,4-addition of [MeOH2]+[Co(CO)4]− to 1 is the only pathway to 2-butenylcobalt tetracarbonyl, CH3CH═CHCH2Co(CO)4 (4), via the protonation of 1 followed by the reaction of the C4 carbocation with the counteranion tetracarbonylcobaltate. In the absence of carbon monoxide, 4 could lose a coordinated carbon monoxide to form (η3-C4H7)Co(CO)3 (7) i...

N-tert-Butyl-trans-α-ethoxycarbonyl-β-phenyl-β-lactam has been prepared in 95 % yield (GC) by the octacarbonyldicobalt-catalyzed carbonylation of ethyl diazoacetate in dichloromethane in the presence of N-tert-butylbenzaldimine at 10 °C and 75 bar pressure of carbon monoxide. The key step of the reaction is the catalytic formation of the highly reactive (ethoxycarbonyl)ketene from both of the intermediary complexes [Co2(CO)7(CHCO2Et)] and [Co2(CO)6(CHCO2Et)2], which is in situ scavenged by the imine in a [2+2] cycloaddition reaction. DFT (PBEPBE/6-31G**) calculations revealed that the reaction follows a two-step mechanism via a noncyclic intermediate with a reaction free energy of –15.9 kcal/mol and a free-energy barrier of 24.7 kcal/mol for the second rate-limiting step. The computation also shows that the formation of the trans isomer is preferred both kinetically and thermodynamically. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The multi-step conversion of sucrose to various C5-oxygenates and alkanes was achieved by integrating various homogeneous and heterogeneous catalytic systems. We have confirmed that the dehydration of sucrose to levulinic and formic acids is currently limited to about 30–40% in the presence of H2SO4, HCl, or Nafion NR50 in water. Performing the dehydration in the presence of a P(m-C6H4SO3Na)3 modified ruthenium catalyst under hydrogen resulted in the in situ conversion of levulinic acid to γ-valerolactone (GVL). Levulinic acid can be hydrogenated to GVL quantitatively by using P(m-C6H4SO3Na)3 modified ruthenium catalyst in water or Ru(acac)3/PBu3/NH4PF6 catalyst in neat levulinic acid. Formic acid can be used for the transfer hydrogenation of levulinic acid in water in the presence of [(η6-C6Me6)Ru(bpy)(H2O)][SO4] resulting in GVL and 1,4-pentanediol. The hydrogenation of levulinic acid or GVL can be performed to yield 1,4-pentanediol and/or 2-methyl-tetrahydrofuran (2-Me-THF). The hydrogenolysis of 2-Me-THF in the presence of Pt(acac)2 in CF3SO3H resulted in a mixture of alkanes. We have thus demonstrated that the conversion of carbohydrates to various C5-oxygenates and even to alkanes can be achieved by selecting the proper catalysts and conditions, which could provide a renewable platform for the chemical industry.

Reactions of the fluorous primary phosphines R f n (CH 2 ) 2 PH 2 [R f n =(CF 2 ) n - 1 CF 3 ; n=6, 8, 10] and R f n ' CH=CH 2 [(n'=6, 8, 10) (1:1; THF, reflux) in the presence of AIBN give the title compounds [R f n (CH 2 ) 2 )[R f n ' (CH 2 ) 2 ]PH [n/n'=6/6 (4, 55%), 8/8 (5, 58%), 10/10 (6, 53%), 8/6 (7, 52%), 10/8 (8, 51%)] as low-melting white solids on up to 10-g scales. The chiral tertiary phosphine [R f 6 (CH 2 ) 2 ][R f 8 (CH 2 ) 2 ][R f 1 0 (CH 2 ) 2 ]P (9) is similarly prepared from 7 and R f 1 0 CH=CH 2 in the presence of VAZO (neat, 100°C; 67%). The reaction of 5 and THF.BH 3 yields the phosphine borane 5.BH 3 (95%). Additions of triphosgene [(CCl 3 O) 2 CO] to 5 or R f 8 (CH 2 ) 2 PF 2 give [R f 8 (CH 2 ) 2 ] 2 PCl or R f 8 (CH 2 ) 2 PCl 2 , which are characterized in situ. The CF 3 C 6 F 1 1 /toluene partition coefficients of 4-9 increase with the number and lengths of the R f n segments.

Kinetics of the reaction of octacarbonyl dicobalt with ethyl diazoacetate leading to [μ 2 -{ethoxycarbonyl(methylene)}-μ 2 -(carbonyl)-bis(tricarbonyl-cobalt)] ( Co - Co ) ( 1 ), dinitrogen, and carbon monoxide were investigated at 10 °C in heptane solution. The initial rate of the reaction was measured by following both the gas evolution and the decrease of the octacarbonyl dicobalt concentration. The rate is first order with respect to octacarbonyl dicobalt and a complex order with respect to ethyl diazoacetate and carbon monoxide depending on the ratio of their concentrations. This is in accord with the formation of a heptacarbonyl dicobalt reactive intermediate ( k 1 (10 °C) = (1.22 ± 0.06) × 10 −3 s −1 ) for which carbon monoxide and ethyl diazoacetate compete ( k −1 / k 2 (10 °C) = 1.34 ± 0.07).

The triphenylphosphane substituted derivatives Co2(CO)6(CHCO2Et)(PPh3), [μ2-{ethoxycarbonyl(methylene)}-μ2-(carbonyl)-(tricarbonyl-cobalt)-(triphenylphosphane-dicarbonyl-cobalt) (Co Co)] (3) and Co2(CO)5(CHCO2Et)(PPh3)2, [μ2-{ethoxycarbonyl-(methylene)}-μ2-(carbonyl)-bis(triphenylphosphane-dicarbonyl-cobalt) (Co–Co)] (4) were prepared from the known Co2(CO)7(CHCO2Et) (1) and Co2(CO)6(CHCO2Et)2 (2) complexes with triphenylphosphane. The new complexes 3 and 4 as well as Co2(CO)7(PPh3), Co2(CO)6(PPh3)2, and Co2(CO)6 (dppm) (dppm = Ph2PCH2PPh2) were found to be suitable catalyst precursors in the selective carbonylation of ethyl diazoacetate to diethyl malonate in the presence of ethanol.

In the presence of 1 mol% octacarbonyl dicobalt ethyl diazoacetate can be transformed at room temperature and carbon monoxide pressure selectively into diethyl 2-diazo-3-oxo-pentanedicarboxylate or in the presence of an alcohol (methanol, ethanol, tert -butanol), phenol or diethylamine into the corresponding malonic acid derivatives in high yields. Ethoxycarbonylcarbene-bridged dicobalt carbonyl complexes [μ 2 -{ethoxycarbonyl(methylene)}-μ 2 -(carbonyl)-bis(tricarbonyl-cobalt)( Co – Co )] and [di-μ 2 (ethoxycarbonyl(methylene)}-bis(tricarbony-cobalt)( Co–Co )] proved to be intermediates in the catalytic reactions.

The addition of galvinoxyl or 2,2-diphenyl-1-picrylhydrazyl to octacarbonyldicobalt in n-octane solution results in the loss of all carbon monoxide ligands and the formation of Co(II)-containing products.

The initial rate of carbon monoxide evolution in the reaction of Octacarbonyl dicobalt with 2,2,6,6-tetramethylpiperidin-1-oxyl free radical (TEMPO) at 15°C in n-octane solution leading to the 16e complex (TEMPO)Co(CO)2 was found to be first order with respect to the TEMPO concentration, 0.5 order with respect to the Co2(CO)8 concentration, and negative 0.5 order with respect to the CO concentration. Scavenging ·Co(CO)4 and ·Co(CO)3 by the free radical TEMPO in the rate-determining steps are in accord with the kinetic observation. The observed rate constant is kobs = 6.4 × 10−5 s−1.

The development of new types of β-lactam antibiotics is a relevant field of contemporary pharmaceutical research. Although many types of antibiotics are available on the market and widely used, β-lactam antibiotics are considered to be one of the best choice as they are highly effective while having reasonable safety profiles. The wide application however has led to the appearance of resistant bacteria suppressing their efficacy. In the last decade fewer and fewer new antibiotics have been launched into the market, however more and more multiresistant germs have appeared posing significant threats especially to patients who are suffering from chronic diseases and have weakened immune systems. The development of new, highly efficient antibiotics is now direly needed. One of the options to accelerate β-lactam antibiotic research is the development of alternative robust, convenient, versatile and cheap synthetic procedures in which the β-lactam molecules can be easily synthesized with the desired diastereoselectivity. The most general way to introduce diastereoselectivity in the chemical reactions is the application of chiral catalyst systems. While there are several systems for the synthesis of β-lactams the transition metal assisted Staudinger reaction – [2 + 2] cycloaddition between a ketene and an imine – remained the most simple and most versatile methodology. The motivation behind this brief review is to draw the chemical community's attention to the relevance and applicability of transition metal promoted Staudinger reactions in β-lactam based antibiotic development. This article summarizes the most relevant pioneer works completed on this field in order to open new ideas for the forthcoming organometallic systems based bioactive material development.

Polypentenamer was synthetized by equilibrium ring-opening metathesis polymerization (ROMP) using well-defined ruthenium catalyst systems. It was found that the equilibrium time is influenced by the catalyst loading or the catalyst activity, however as expected, the overall cyclopentene conversion is determined only by the applied reaction temperature. Equilibrium of the growing chain and monomer was observed and the activation enthalpy and entropy were determined as: ΔH = −5.6 kcal mol^(−1); ΔS = −18.5 cal mol^(−1) K^(−1). So far these values are the lowest which are reported for cyclopentene polymerization catalyst systems. This unique feature of the equilibrium polymerization opens a way for the synthesis of durable, environmentally friendly elastomers where tires can be not only synthetized but also readily recycled by the same transition metal catalyst system.

The pyridine-modified cobalt-catalyzed hydromethoxycarbonylation of 1,3-butadiene (1) starts by the disproportionation of Co2(CO)8 to [CoPy6][Co(CO)4]2 followed by the formation of HCo(CO)4 (3). The addition of 3 to 1 leads to CH3CHCHCH2Co(CO)4 (4), which, depending on the conditions, can undergo facile CO insertion to yield CH3CHCHCH2COCo(CO)4 (5) or reversible decarbonylation to form η3-C4H7Co(CO)3(7). Pyridine accelerates the conversion of 7 to methyl-3-pentenoate (2) and the methanolysis of 5.

A fluorous phosphine analogue of Grubbs' second generation olefin metathesis catalyst, (H(2)IMes)((R(f8)(CH(2))(2))(3)P)(Cl)(2)Ru(=CHPh) (1; H(2)IMes/R(f8) = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene/(CF(2))(7)CF(3)) is crystallized and the X-ray structure analyzed in detail. The bond lengths and angles about ruthenium are compared to those of two solvates and five derivatives of Grubbs' second generation catalyst. All exhibit distorted square pyramidal geometries in which the alkylidene ligands occupy apical positions, and geometric trends are interpreted with the help of density functional calculations. The perfluoroalkyl groups (1) exhibit helical conformations, as manifested by various torsional relationships, (2) segregate in the lattice, and (3) align in pairs of opposite helical chiralities.

The aim of the green chemistry is to develop chemical products and processes having minimal use and generation of hazardous chemicals and low energy requirement. Catalytic reagents are considered to be green tools to synthesize organic molecules as they basically open an alternative synthetic route to target molecules by lowering the energy barriers of the reactions while keeping the selectivity and the yield of the reactions high. Polynorbornene - which can be synthesized by ring opening methathesis polymerization (ROMP) with Grubbs’ catalyst - is used in the automotive and appliance industries mainly as vibration and noise isolators and produced thousands of tons per year scale. It is well known that during the catalytic cycle the reverse phosphine reassociation step competes with the subsequent alkene binding step on the coordination sphere of the catalyst, slowing the observed rate constant. One option to improve the activity of the catalyst system is rolling back the reassociation step by th...

Reactions of the diphosphine 1,3-C6H4(CH2PH2)2 and fluorous alkenes H2C=CHR(fn)(R(fn)=(CF2)(n-1)CF3; n = 6, 8) at 75 degrees C in the presence of AIBN give the title ligands 1,3-C6H4(CH2P(CH2CH2R(fn))2)2(3-R(fn)) and byproducts 1,3-C6H4(CH3)(CH2P(CH2CH2R(fn))2)(4-R(fn)) in 1 : 3 to 1 : 5 ratios. Workups give -R(fn) in 4--17% yields. Similar results are obtained photochemically. Reaction of 1,3-C6H4(CH2Br)2 and HP(CH2CH2R(f8))2 (5) at 80 degrees C (neat, 1 : 2 mol ratio) gives instead of simple substitution the metacyclophane [1,3-C6H4(CH2P(CH2CH2R(f8))2 CH2-1,3-C(6)H(4)CH(2)P[lower bond 1 end](CH2CH2R(f8))2C[upper bond 1 end]H2](2+)2Br-, which upon treatment with LiAlH(4) yields 3-R(f8)(20%), 4-R(f8), and other products. Efforts to better access 3-R(f8), either by altering stoichiometry or using various combinations of the phosphine borane (H3B)PH(CH2CH2R(f8))2 and base, are unsuccessful. Reactions of 3-R(fn) with Pd(O2CCF3)2 and [IrCl(COE)2]2(COE=cyclooctene) give the palladium and iridium pincer complexes (2,6,1-C6H3(CH2 P(CH2CH2R(fn))(2)(2)Pd(O2CCF3)(10-R(fn); 80-90%) and (2,6,1-C6H3(CH2P(CH2CH2R(f8))2)2)Ir(Cl)(H)(11-R(f8); 29%), which exhibit CF3C6F(11)/toluene partition coefficients of96 :4. The crystal structure of 10-R(f8) shows CH2CH2R(f8) groups with all-anti conformations that extend in parallel above and below the palladium square plane to create fluorous lattice domains. NMR monitoring shows a precursor to 11-R(f8) that is believed to be a COE adduct.

Combinatorial chemistry is a high throughput experimental technique that has significantly changed the drug discovery process in the pharmaceutical industry and become common practice for drug research. Combinatorial synthesis and rapid screening techniques have been applied to the development of homogeneous catalysts and for the optimization of reaction conditions. In contrast to classical experimental design, well-designed high throughput screening systems can test more catalysts a week than was previously done in a year. This could lead to significant savings in research and development costs. This article provides a survey of the most frequently used combinatorial methods and screening systems applied in homogeneous catalysts discovery. Several examples are presented on the identification of most effective homogeneous catalysts for hydrogenation, hydrosilylation, cyclopropanation, epoxidation, etc. Keywords: combinatorial chemistry; high throughput screening; homogeneous catalysts; asymmetric catalysts; split-and-mix technique; parallel screening; ligand synthesis

The development of new types of β-lactam antibiotics is a relevant field of contemporary pharmaceutical research. Although many types of antibiotics are available on the market and widely used, β-lactam antibiotics are considered to be one of the best choice as they are highly effective while having reasonable safety profiles. The wide application however has led to the appearance of resistant bacteria suppressing their efficacy. In the last decade fewer and fewer new antibiotics have been launched into the market, however more and more multiresistant germs have appeared posing significant threats especially to patients who are suffering from chronic diseases and have weakened immune systems. The development of new, highly efficient antibiotics is now direly needed. One of the options to accelerate β-lactam antibiotic research is the development of alternative robust, convenient, versatile and cheap synthetic procedures in which the β-lactam molecules can be easily synthesized with the desired diastereoselectivity. The most general way to introduce diastereoselectivity in the chemical reactions is the application of chiral catalyst systems. While there are several systems for the synthesis of β-lactams the transition metal assisted Staudinger reaction – [2 + 2] cycloaddition between a ketene and an imine – remained the most simple and most versatile methodology. The motivation behind this brief review is to draw the chemical community's attention to the relevance and applicability of transition metal promoted Staudinger reactions in β-lactam based antibiotic development. This article summarizes the most relevant pioneer works completed on this field in order to open new ideas for the forthcoming organometallic systems based bioactive material development.