The WCl6-e-Al-CH2Cl2 catalyzed polypentenamer formation via ring-opening metathesis polymerization (ROMP)

The synthesis of polypentenamer by an electrochemically generated metathesis polymerization catalyst from methylene chloride solution of WCl₆ was investigated. The active species formed by electroreduction of this salt under controlled potential of +900 mV at a platinum cathode with an aluminum anode were found to catalyze the ring-opening metathesis polymerization (ROMP) of cyclopentene, monocyclic olefin of relatively low strain, in high yield (89%) and at short period (32 min) under mild conditions. The effect of reaction parameters, e.g., olefin/catalyst ratio, reaction time, electrolysis time, catalyst aging, on the polymerization yield have been studied. The resulting polymer has been characterized by ¹H and ¹³C NMR, IR and gel permeation chromatography (GPC) techniques. Analysis of the polypentenamer microstructure by means of ¹³C NMR spectroscopy indicates that the polymer contains a mainly trans stereoconfiguration of the double bonds (σ_c = 0.31) and a slightly blocky distribution (r_tr_c > 1) of cis and trans double bond dyads (r_tr_c = 1.44). However, this electrochemical system is reluctant to facilitate the competing vinyl type addition polymerization reactions.     

New 2-(2-pyridyl)piperidines: synthesis, complexation of palladium and catalytic activity in Suzuki reaction

The syntheses of novel 2-(2-pyridyl)-6-alkyl piperidines are reported using intramolecular Mannich-based methodology. Preliminary evaluation of the catalytic activity of the corresponding (diamine)Pd(II) complexes in the preparation of biaryl derivatives through Suzuki-type coupling reaction showed high to quantitative conversions and catalyst loadings as low as 10⁻³ mol %.     

Enantioselective cyanosilylation of aldehydes catalyzed by a novel N,N′-dioxide-Ti(OPr)4 bifunctional catalyst

A novel bifunctional asymmetric catalyst containing N-oxide and titanium(IV) was developed and applied to the asymmetric cyanosilylation of aldehydes. Optically active trimethylsilyl cyanohydrin ethers were obtained up to 99% yield and 80% ee in the presence of 5 mol % catalyst loading at −78 °C. Based on the experimental results, the catalytic cycle was proposed as a pathway in which Lewis acid and Lewis base activated aldehyde and trimethylsilylcyanide (TMSCN), respectively.     

Pyrrole synthesis using a tandem Grubbs’ carbene-RuCl3 catalytic system

A straightforward pyrrole synthesis from diallylamines is developed by using a tandem catalyst system leading to ring-closing metathesis with the second generation Grubbs’ catalyst (10%) followed by dehydrogenation in the presence of RuCl₃ × H₂O (2%).     

Alkyne metathesis: toward simplicity and efficiency

No catalyst pre-activation, no suicide alkyne, and no additive is required in an extremely simple procedure for the metathesis of alkyl-, alkenyl-, and aryl-propynes: just mix Mo(CO)₆, p-chlorophenol, and the alkyne in 1,2-dichloroethane, heat at 85 °C for 9-24 h, and the symmetrical alkyne is produced in ca. 95% yield.     

Hiyama reaction of aryl bromides with arylsiloxanes catalyzed by a reusable palladium(II)/cationic bipyridyl system in water

A Pd(NH₃)₂Cl₂/cationic bipyridyl catalytic system catalyzed the cross-coupling reaction of aryl bromides with arylsiloxanes in water under aerobic conditions in the presence of NaOH to afford biaryls in good to high yields. The reaction was performed at 120 °C and the loading amount of catalyst can be as low as 0.001 mol %. After extraction, the residual aqueous phase can be reused several times with only a slight decrease in activity.     

A recyclable palladium-catalyzed modified Friedländer quinoline synthesis

2-Aminobenzyl alcohol reacts with an array of ketones in toluene/poly(ethylene glycol) (PEG-2000) at 100 °C in the presence of a palladium catalyst along with KOH under an atmosphere of air to give the corresponding quinolines in good yields. The catalytic system could be recovered and reused five times without any loss of catalytic activity.     

Recyclable N-heterocyclic carbene/palladium catalyst on graphene oxide for the aqueous-phase Suzuki reaction

Graphene oxide (GO) was functionalized with a N-heterocyclic carbene (NHC) precursor, 3-(3-aminopropyl)-1-methylimidazolium bromide ([APMIm][Br]) for the immobilization of palladium catalyst. The GO-supported NHC precursor (IMGO) formed a stable complex with Pd(OAc)₂ (GO–NHC–Pd), which showed excellent catalytic activity and fast reaction kinetics in the aqueous-phase Suzuki reaction of aryl bromides and chlorides at relatively mild conditions (1 h at 50 °C). The GO–NHC–Pd catalyst was reused several times without any loss of its catalytic activity in the Suzuki reaction of aryl bromide.     

A convenient procedure for palladium catalyzed cyanation using a unique bidentate phosphorus ligand

A palladium complex bearing 1,2-diphenyl-3,4-diphosphinidenecyclobutene ligand (DPCB) has been used to facilitate the catalytic cyanation of aryl bromides. A series of substituted benzonitriles was prepared in good to high yields by the treatment of the corresponding aryl bromides with Zn(CN)₂ in N-methyl-2-pyrrolidone in the presence of 2-4 mol % catalyst at 100 °C for 16 h.     

Polymeric salen-Ti(IV) or V(V) complex catalyzed asymmetric synthesis of O-acetylcyanohydrins from KCN, Ac2O and aldehydes

Polymeric salen-Ti(IV) and V(V) complexes were employed in the enantioselective O-acetyl cyanation of aldehydes with potassium cyanide and acetic anhydride. The crosslinked polymeric salen-Ti(IV) catalyst exhibited good activities and enantioselectivities, up to 91% ee with 99% conversion was obtained at −20 °C with 1 mol% of catalyst (based on bimetallic catalytic unit). Moreover, six consecutive recyclings with the easily recovered crosslinked polymeric catalyst showed no obvious decrease in either activity or enantioselectivity. Linear polymeric salen-V(V) catalyst showed good catalytic efficiency too, up to 94% ee with 99% conversion was obtained at −42 °C with 5 mol% of catalyst.     

A practical asymmetric conjugate addition to cyclic enones with chiral bifunctional Ru amido catalysts

A practical asymmetric C-C bond formation to synthetically useful β-chiral cyclic ketones (>99% ee) using bifunctional chiral amido Ru catalysts under an S/C = 1000, the highest ratio achieved so far in the literature for this class of reactions, is described. The catalytic reactivity decreases in the order of Ru(Msdpen)(hmb) > Ru(Pfbsdpen)(hmb) > Ru(Tsdpen)(hmb) > Ru(PMsdpen)(hmb), where Ru(Pfbsdpen)(hmb) is a newly developed chiral bifunctional catalyst. Complex Ru(Msdpen)(hmb) was identified as the best in terms of reactivity and enantioface selectivity, whereas Ru(PMsdpen)(hmb) gave unsatisfactory results. An importance of the NH proton in the bifunctional catalyst for determining the enantioselectivity has been experimentally demonstrated. Valuable information for the reaction mechanism was accumulated.     

Solvent effect in cis-1,4 polymerization of 1,3-butadiene by a catalyst based on neodymium

In this work a laboratory polymerization scale process was studied for the production of polybutadiene with high content of cis-1,4 repeating units. A Ziegler-Natta catalytic system based on neodymium versatate (catalyst), diisobutylaluminium hydride (cocatalyst) and tert-butyl chloride (chlorinating agent) was used. The influence of solvent nature (pure grade) and possible contaminants (electron donors) in a recovered solvent from a butadiene-styrene anionic polymerization industrial plant on the stereoselectivity and catalytic activity, molecular weight and molecular weight distribution of the resultant polybutadienes was studied. The polymers were characterized by infrared spectroscopy and size exclusion chromatography. Polybutadienes with cis-1,4 units content in the range of 99-98% were produced. The polymers weight-average molecular weight, , varied from 2.23 × 10⁵ to 4.47 × 10⁵ and the molecular weight distribution, MWD, from 3.1 to 5.1.     

Synthesis and Catalytic Activity of a Grubbs‐Hoveyda Pre‐catalyst Having a Trimeric Resting State

A Grubbs‐Hoveyda pre‐catalyst having a trimeric resting state based on 2,4,6‐trichloro‐1,3,5‐triazine was synthesized and the complex was characterized by NMR, HRMS and elemental analysis. The activity of this complex for ring‐closing metathesis (RCM) was investigated. The catalytic system possesses high catalytic activity for many different olefin substrates.     

“On-water” synthesis of 3-substituted indoles via Knoevenagel/Michael addition sequence catalyzed by Cu doped ZnS NPs

Cu doped ZnS NPs represent a green catalyst for an ‘on-water’ one-pot rapid synthesis of 3-substituted indole derivatives via Knoevenagel/Michael addition reaction of indane-1,3-dione, aromatic aldehydes, and indole. The catalytic activity of Cu doped ZnS NPs was about sevenfold higher as compared to the ZnS NPs. The Cu doped ZnS NPs catalyst could be recovered and reused for five reaction cycles, giving a total TOF = 201 h⁻¹.     

Asymmetric hydrogenation of methyl α-benzamido cinnamate in ionic liquid solvent

The room temperature ionic liquid EMIMOTf was employed as the sole reaction solvent for the asymmetric hydrogenation of methyl α-benzamido cinnamate. Under conditions of 60 psi hydrogen and 50 °C for 24 h, near quantitative conversions were observed using both the achiral DiPFc-Rh catalyst, and the chiral EtDuPHOS-Rh catalysts. Enantiomeric excess of 89% ee was observed for hydrogenations carried out with the chiral catalyst.     

Carboxymethylcellulose‐supported palladium nanoparticles generated in situ from palladium(II) carboxymethylcellulose as an efficient and reusable catalyst for ligand‐ and base‐free Heck–Matsuda and Suzuki–Miyaura couplings

A novel palladium(II) carboxymethylcellulose (CMC‐Pd^II) was prepared by direct metathesis from sodium carboxymethylcellulose and PdCl₂ in aqueous solution. Its catalytic activities were explored for Heck–Matsuda reactions of aryldiazonium tetrafluoroborate with olefins, and Suzuki–Miyaura couplings of aryldiazonium tetrafluoroborate with arylboronic acid. Both reactions proceeded at room temperature in water or aqueous ethanol media without the presence of any ligand or base, to provide the corresponding cross‐coupling products in good to excellent yields under atmospheric conditions. The CMC‐Pd^II and carboxymethylcellulose‐supported palladium nanoparticles (CMC‐Pd⁰) formed in situ in the reactions were characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, inductively coupled plasma atomic emission spectrometry, and scanning and transmission electron microscopies. The homogeneous nature of the CMC‐Pd⁰ catalyst was confirmed via Hg(0) and CS₂ poisoning tests. Moreover, the CMC‐Pd⁰ catalyst could be conveniently recovered by simple filtration and reused for at least ten cycles in Suzuki–Miyaura reactions without apparently losing its catalytic activity. The catalytic system not only overcomes the basic drawbacks of homogeneous catalyst recovery and reuse but also avoids the need to fabricate palladium nanoparticles in advance. Copyright © 2015 John Wiley & Sons, Ltd.     

An efficient method for the multicomponent synthesis of multisubstituted pyridines,a rapid procedure using Au/MgO as the catalyst

Au/MgO proved to be a highly efficient and reusable catalyst for multicomponent coupling reactions at 70 °C. The synthesized multisubstituted pyridines were obtained in high yields and in short reaction times. With facile work-up, the novel catalyst can be readily recovered after the reaction and reused without any loss of its catalytic activity.     

Hydrotalcites as catalysts for the Baeyer-Villiger oxidation of cyclic ketones with hydrogen peroxide/benzonitrile

Hydrotalcites (HTs) in variable Mg/Al ratios were used as catalysts for the Baeyer-Villiger (BV) oxidation of cyclic ketones with hydrogen peroxide. All HTs studied were found to be active in the BV oxidation of cyclohexanone, their activity increases with increasing Mg/Al ratio. The reaction, which was conducted under very mild conditions (viz. atmospheric pressure and a temperature of 70 °C), provided conversions above 70% with 100% selectivity only after 6 h. This outcome was found to require the presence of a nitrile in the reaction medium, so a mechanism involving adsorption of the nitrile and cyclohexanone onto the catalyst is proposed that is consistent with the experimental results. Based on the proposed mechanism, the presence of a surfactant should result in improved conversion and catalytic activity, as was indeed observed with sodium dodecylsulfate in the reaction medium. The best catalyst among those tested was used with other cyclic ketones and found to provide excellent conversion and selectivity results in most cases.     

Polymerization of 5-norbornene-2-methyl acetate catalyzed by air-stable cationic (η-substituted allyl) palladium complexes of N-heterocyclic carbene

In situ generated cationic (η³-substituted allyl) palladium N-heterocyclic carbene (NHC) complexes are air-stable active catalysts for the olefin polymerization of (bicyclo[2.2.1]hept-5-en-2-yl)methyl acetate (5-norbornene-2-methyl acetate) (endo:exo = 7:3). Catalytic activities, polymer yields, molecular weights, and molecular weight distributions of polymers were investigated under various reaction conditions. The catalytic activity was highly dependent not only on the reaction condition such as a solvent or the reaction temperature but also on the structure of the catalyst that include substituents of the allyl group in the catalyst and the counter anion. As the bulkiness of the allyl group increased, the catalytic activity of the catalysts increased.     

An efficient and simple ligand from phthalandione for palladium-catalyzed Suzuki reaction in aqueous media

An efficient and simple ligand derived from phthalandione was used for palladium catalyzed Suzuki coupling reaction in water/ethanol (V/V = 2/1) under aerobic conditions. The reaction exhibited a high catalytic efficiency even with lower Pd loading (0.002 mol %). In this work, the catalyst could be successfully used in coupling reaction between various aryl halides with phenylboronic acid in excellent yields with high turnover number (TON) (the maximal TON was up to 49,000 for the reaction of bromobenzene with phenylboronic acid). Moreover, this new ligand had been elucidated by ¹H NMR, ¹³C NMR and X-ray crystal diffraction.