Ethylene Atmosphere Research Articles

ChemInform Abstract: Nonmetathetic Activity of Ruthenium Alkylidene Complexes: 1,4‐Hydrovinylative Cyclization of Multiynes with Ethylene.

AbstractGrubbs′ second generation catalyst efficiently catalyzes the 1,4‐hydrovinylative cyclization of tetraynes (I), (VI) and triynes (VIII) under an ethylene atmosphere.

Reproductive Regulating Pheromones of Queen Ant: A Short and Versatile Synthesis of 3,11-Dimethylheptacosane

Social behavior of insects always fascinates human beings as they appear to maintain good order and communication in the society. Insects have developed sophisticated chemical communication systems using their pheromones for the purpose. Among the pheromones, cuticular wax is used to recognize group members from non-members. In ants, there have been identified close to 1,000 cuticular hydrocarbons (CHCs) and the composition of CHCs of cuticles works for the discrimination between their friends and foes. Some species of ants are known to use cuticular wax of the dead ants in other colonies to disguise their identity when they invade other colonies. It was known that the antennae of ants recognize the composition of the CHCs but the exact mechanism of this recognition has not been well studied. The CHCs on the cuticles are also used to distinguish the queen ant from other fertile ants. Queen ants produce 3,11dimethylated linear hydrocarbons longer than C26 (Figure 1). Interestingly, only the odd numbered carbon chains ranging from 27 to 33 are found in insect society. These CHCs are also coated on the eggs of the queen but do not exist on those of other ants, which allow ants to distinguish those eggs and destroy the latter by eating to control their social hierarchy. We became interested in the recognition mechanism of the different composition of CHCs and the effect of the disruption of CHC composition on the social behavior of ants. For these studies, we need to devise a versatile synthetic route to these branched hydrocarbons. Herein, we report the first synthesis of 3,11-dimethylheptacosane (1) through a short and versatile synthetic route. The synthetic analysis of 3,11-dimethylheptacosane (1) shows that intermolecular enyne metathesis can allow to introduce two methyl group on the chain and the overall chain length could be controlled by using an alkyne with proper chain length (Scheme 1). Two methyl groups of 1 can be obtained from two conjugated dienes of 2. These two diene fragments, 3 and 4, can be prepared through enyne metathesis of tosylated butynol 6 with proper olefin. This synthesis would not require any protecting group and allows that alkyne 5 could be replaced by other alkynes with different chain length for the synthesis of all possible CHC pheromones. The synthesis started from 3-butynol to produce the corresponding tosylate 6. The alkyne 6 was treated with the second generation Grubbs catalyst (Grubbs II) under ethylene atmosphere to produce diene 3. Since allyl bromide was not

Observation of room-temperature formation of carbon nanotubes as a result of the detachment of a gold nanolayer from a glass substrate

The glass surface morphology after the detachment of a 50–200nm-thick gold layer deposited on a glass substrate was investigated by the scanning electron microscopy for the three types of glass substrates: smooth plate glass surface without pre-treatment, chemical etched glass and glass surface modified by surface ion exchange process. It was found that the boundaries' morphology of the detached gold fragments depends essentially on the microrelief of surface for each kind of the glass substrate. It was confirmed by X-ray energy dispersive spectroscopy that carbon nanotubes are formed near the detachment boundaries of the gold nanolayer's fragment from glass substrate and consequent storage of these samples in the air at room temperature.In the authors' opinion, the observed mechanochemical effect associated with the detachment of thin gold layer fragment from glass substrate leads to the increase of the gold catalytic activity and to carbon nanotubes formation in the air that contains carbon impurities. This assumption is confirmed, in particular, by the formation of carbon nanotubes after the detachment of thin gold layer fragment from the glass substrate surface and storage in an ethylene atmosphere.

Ring-opening metathesis and ring-closing metathesis of bicyclo[4.2.0]octene-ynes: Application to the synthesis of tricyclic compounds

Ring-opening metathesis and ring-closing metathesis (ROM-RCM) of bicyclo[4.2.0]octene-ynes and their application to the synthesis of tricyclic derivatives have been demonstrated using a second-generation ruthenium carbene complex. When bicycloalkene having a propargylamino group as an alkyne tether was reacted with a second-generation ruthenium carbene complex under an ethylene atmosphere, ROM-RCM proceeded to give tricyclic heterocycles in good yield. On the other hand, when the effect of the substituent on the alkyne was examined, cross metathesis (CM) of the alkyne part with ethylene proceeded to provide a conjugated diene derivative.

C−H Bond Activation Reactions in π-Allene−Osmium−Triisopropylphosphine Complexes with Cyclopentadienyl or Hydridotris(pyrazolyl)borate Ligands: Formation of Isopropenyldiisopropylphosphine versus Hydride−Alkenylcarbyne Derivatives

The reactions of the bis(solvento) complexes [OsCp(MeCN)2(PiPr3)]PF6 (1; Cp = cyclopentadienyl) and [OsTp(κ1-OCMe2)2(PiPr3)]BF4 (1a; Tp = hydridotris(pyrazolyl)borate) with allenes have been investigated. Complex 1 reacts with 1-methyl-1-(trimethylsilyl)allene and 1,1-dimethylallene to give the π-allene derivatives [OsCp(η2-CH2═C═CRMe)(MeCN)(PiPr3)]PF6 (R = SiMe3 (2), Me (3)). In fluorobenzene at 80 °C, complexes 2 and 3 are moderately stable and evolve into the isopropenyldiisopropylphosphine derivative [OsCp{κ3P,C,C-PiPr2[C(Me)═CH2]}(MeCN)]PF6 (4) by hydrogen transfer from an isopropyl substituent of the phosphine to the coordinated double bond of the allene. Under an ethylene atmosphere the acetonitrile ligand of 4 is displaced by the olefin. The resulting π-ethylene derivative [OsCp(η2-CH2═CH2){κ3P,C,C-PiPr2[C(Me)═CH2]}]PF6 (5) is obtained through a one-pot synthesis procedure by the stirring of 3 in fluorobenzene at 80 °C under 2 atm of ethylene. Treatment of 2 and 3 with dimethyl acetylenedicarboxyl...

Effects of abscisic acid, ethylene and sugars on the mobilization of storage proteins and carbohydrates in seeds of the tropical tree Sesbania virgata (Leguminosae)

Endospermic legumes are abundant in tropical forests and their establishment is closely related to the mobilization of cell-wall storage polysaccharides. Endosperm cells also store large numbers of protein bodies that play an important role as a nitrogen reserve in this seed. In this work, a systems approach was adopted to evaluate some of the changes in carbohydrates and hormones during the development of seedlings of the rain forest tree Sesbania virgata during the period of establishment. Seeds imbibed abscisic acid (ABA), glucose and sucrose in an atmosphere of ethylene, and the effects of these compounds on the protein contents, α-galactosidase activity and endogenous production of ABA and ethylene by the seeds were observed. The presence of exogenous ABA retarded the degradation of storage protein in the endosperm and decreased α-galactosidase activity in the same tissue during galactomannan degradation, suggesting that ABA represses enzyme action. On the other hand, exogenous ethylene increased α-galactosidase activity in both the endosperm and testa during galactomannan degradation, suggesting an inducing effect of this hormone on the hydrolytic enzymes. Furthermore, the detection of endogenous ABA and ethylene production during the period of storage mobilization and the changes observed in the production of these endogenous hormones in the presence of glucose and sucrose, suggested a correlation between the signalling pathway of these hormones and the sugars. These findings suggest that ABA, ethylene and sugars play a role in the control of the hydrolytic enzyme activities in seeds of S. virgata, controlling the process of storage degradation. This is thought to ensure a balanced flow of the carbon and nitrogen for seedling development.

Ring‐Closing Metathesis of Ene‐Ynamide: Application to the Synthesis of Medium‐Sized Cyclic Dienamide

AbstractSummary: Ring‐closing metathesis (RCM) of ene‐ynamide, which could be applied to the synthesis of various heterocycles containing 7‐ and 8‐membered rings, was investigated. Ene‐ynamides are easily synthesized by the known method. When a toluene solution of ene‐ynamide was stirred in the presence of a catalytic amount of second‐generation ruthenium carbene complex 1 under an ethylene atmosphere, RCM proceeded smoothly to provide a heterocyclic compound having a diene moiety in good to high yield. A substituent of the ynamide moiety affected the yield of the cyclized product.

ChemInform Abstract: Dehydrogenation of D-Glycals by Palladium Supported on Activated Charcoal under Ethylene Atmosphere: Synthesis of 1,5-Anhydrohex-1-en-3-uloses.

ChemInform Abstract: Dehydrogenation of D-Glycals by Palladium Supported on Activated Charcoal under Ethylene Atmosphere: Synthesis of 1,5-Anhydrohex-1-en-3-uloses.

Asymmetric hydrovinylation of unactivated linear 1,3-dienes.

Monosubstituted acyclic (E)-1,3-dienes undergo efficient hydrovinylation giving (Z)-3-alkylhexa-1,4-dienes upon treatment with catalytic amounts of bidentate phosphine-CoCl(2) complexes {[P~P](CoCl(2))} and Me(3)Al in an atmosphere of ethylene. The regioselectivity of the reaction (i.e., 1,4- or 1,2-addition) depends on the nature of the ligand and temperature at which the reaction is carried out. Complexes derived from (RR)-DIOP and (SS)-BDDP at -45 degrees C give very high enantioselectivities for several prototypical 1,3-dienes. In sharp contrast to the corresponding Ni(II)-catalyzed hydrovinylation, 1-aryl-substituted 1,3-dienes give almost exclusively achiral linear 1,4-addition products, unless the 2-position is also substituted. Solid-state structures of the precatalysts are presented.

Silyl and σ-silane ruthenium complexes: Chloride substituent effects on the catalysed silylation of ethylene

Silylation of ethylene by the chlorosilanes HSiMe(2)Cl and HSiMeCl(2) was catalysed by the bis(dihydrogen) complex RuH(2)(eta(2)-H(2))(2)(PCy(3))(2) (1). Dehydrogenative silylation leading to the formation of the corresponding vinylsilanes was in competition with hydrosilylation. The rate and selectivity of the reactions were influenced by the number of chloro substituents and the ethylene pressure. A comparative mechanistic study was performed in toluene-d(8) with the two chlorosilanes. Reaction of 1 with an excess of HSiMe(2)Cl (10 equiv.) produced the sigma-silane complexes RuH(2)(eta(2)-H(2))(eta(2)-HSiMe(2)Cl)(PCy(3))(2) (2Me(2)Cl), RuH(2)(eta(2)-HSiMe(2)Cl)(2)(PCy(3))(2) (3Me(2)Cl) and the silyl complex RuCl(SiMe(2)Cl)(eta(2)-H(2))(PCy(3))(2) (4Me(2)Cl), all characterised by multinuclear NMR spectroscopy. Complexes 2Me(2)Cl and 3Me(2)Cl adopt a cis configuration for the two bulky phosphine ligands as a result of stabilising SISHA (Secondary Interactions between Silicon and Hydrogen Atoms) interactions. Complex 4Me(2)Cl resulted from the stoichiometric reaction of HSiMe(2)Cl with 1 producing RuHCl(eta(2)-H(2))(PCy(3))(2)in situ which further reacted with evolution of H(2) and formation of 4Me(2)Cl. When reacting 1 with 10 equiv. of HSiMeCl(2), the corresponding complexes 3MeCl(2) and 4MeCl(2) were detected as well as traces of 2MeCl(2). The reactivity toward ethylene was then examined. Under catalytic conditions (excess silane in toluene-d(8), ethylene atmosphere) only two compounds could be characterised: free PCy(3) and the new (eta(6)-aryl)(disilyl) complexes of the general formula Ru(eta(6)-C(6)D(5)CD(3))(SiMe(3-n)Cl(n))(2)(PCy(3)) (6Me(3-n)Cl(n)-d(8), n = 1,2). The X-ray structure of 6MeCl(2) was obtained on a single-crystal at 160 K. When only 2 equiv. of HSiMe(2)Cl were added, the ethylene(silyl) complex RuH(SiMe(2)Cl)(C(2)H(4))(PCy(3))(2) (7Me(2)Cl) was obtained in addition to the organic products resulting from catalytic hydrogenation, hydrosilylation and dehydrogenative silylation, i.e. C(2)H(6) (major one), C(2)H(3)SiMe(2)Cl and C(2)H(5)SiMe(2)Cl. In the case of 2 equiv. of HSiMeCl(2), upon ethylene addition, 7MeCl(2) was formed in minority compared to a new disilyl complex Ru(SiMeCl(2))(2)(PCy(3))(2) (8MeCl(2)) characterised by NMR spectroscopy and X-ray diffraction on a single crystal at 160 K. In 8MeCl(2), a formal 14-electron species, stabilisation through two agostic C-H bonds of the cyclohexyl groups was ascertained by DFT calculations.

Diphenylphosphino- or Dicyclohexylphosphino-Tethered Boryl Pincer Ligands: Syntheses of PBP Iridium(III) Complexes and Their Conversion to Iridium−Ethylene Complexes

Two hydroborane precursors (1b,c) for PBP pincer ligands bearing phenyl or cyclohexyl groups on phosphorus atoms were synthesized, and their complexation reactions with iridium were investigated. Reaction of hydroborane 1b, bearing phenyl groups, with Ir[P(p-tol)3]2(CO)Cl afforded an 18-electron complex, [PhPBP]Ir(H)(CO)Cl (3b), but reactions with other iridium(I) sources gave complicated mixtures. The characteristic IR peaks in 3b compared with the previously reported tBu-PBP derivative 3a were discussed on the basis of theoretical calculations. Complexation of cyclohexyl-substituted hydroborane 1c with [Ir(C2H4)2Cl]2 afforded a 16-electron complex, [CyPBP]Ir(H)Cl (2c). X-ray structure and computational studies on 2c revealed that the hydride ligand is close [B−H = 1.90(5) A] to the boron atom. Reaction of 2c with LiTMP (TMP = 2,2,6,6-tetramethylpipyridide) under ethylene atmosphere gave monovalent iridium complex [CyPBP]Ir(C2H4) (4c) by a similar procedure to the previously reported [tBuPBP] system. Exp...

Cycloisomerization and [2 + 2]cyclodimerization of 1,5-cyclooctadiene catalyzed with the Ni(COD) 2/BF 3·OEt 2 system

The catalytic system Ni(COD) 2/BF 3·OEt 2 has been studied in conversions of 1,5-cyclooctadiene under argon and ethylene atmosphere. It has been demonstrated that the catalytic system formed under argon exhibits a high effectiveness in cycloisomerization of 1,5-COD surpassing in this characteristic all known nickel complex catalysts (selectivity to bicyclo-[3.3.0]-octene-2 is up to 99.5% at 100% conversion). In the case of ethylene atmosphere the system produces mainly dimers (yield of cyclodimers above 70%). It has been shown that the catalytic system Ni(COD) 2/BF 3·OEt 2 has the feature of “a living catalyst” consisting in resuming the initial activity with a new portion of 1,5-COD added when the monomer was fully exhausted. The main and side products of the 1,5-COD conversion have been identified with GC-MS and preparative liquid chromatography combined with NMR and IR spectroscopy. Based on EPR and IR spectroscopic data a mechanism for the catalytic performance of the Ni(COD) 2/BF 3·OEt 2 system in argon or ethylene atmospheres is suggested. It has been shown that Ni(0) is oxidized by the Lewis acid to Ni(I) which is stabilized by substrate molecules in a mononuclear form without involvement of conventional organoelement entities. Three sorts of paramagnetic nickel species have been found: ionic complexes containing π-coordinated COD ligands; ionic complexes σ-bonded to COD; complexes as intimate pairs with BF 4 − counter ions. A mechanism for the catalytic conversion of 1,5-cyclooctadiene is proposed.

Syntheses of PBP Pincer Iridium Complexes: A Supporting Boryl Ligand

We synthesized a PBP pincer ligand precursor 2 and demonstrated its complexation with iridium(I) to afford the coordinatively unsaturated [PBP](hydrido)chloroiridium complex 3 via B-H oxidative addition. The reaction of 3 with carbon monoxide produced [PBP](hydrido)chloro(carbonyl)iridium 7. The longer Ir-Cl bond length of 7 than that of 8 revealed a stronger sigma-donor ability of the PBP ligand than that of PCP. Complex 3 was also converted to [PBP](ethylene)iridium(I) complex 9 by the reaction with LiTMP under an ethylene atmosphere.

Effect of Postharvest Temperature and Ethylene on Carotenoid Accumulation in the Flavedo and Juice Sacs of Satsuma Mandarin (Citrus unshiu Marc.) Fruit

The effect of postharvest temperature (5, 20, and 30 degrees C) and ethylene at different temperatures (20 and 5 degrees C) on carotenoid content and composition and on the expression of the carotenoid biosynthesis-related genes was investigated in the flavedo and juice sacs of Satsuma mandarin ( Citrus unshiu Marc.) fruit. Under an ethylene-free atmosphere, storage at 20 degrees C rapidly increased the carotenoid content in flavedo and maintained the content in juice sacs. In contrast, storage at 5 and 30 degrees C gradually decreased the content in juice sacs but slowly increased that in flavedo. Under an ethylene atmosphere, storage at 20 degrees C enhanced the carotenoid accumulation in flavedo more dramatically than found under an ethylene-free atmosphere with distinct changes in the carotenoid composition but did not noticeably change the content and composition in juice sacs. In contrast, storage at 5 degrees C under an ethylene atmosphere repressed carotenoid accumulation with changes in the carotenoid composition in flavedo but did not clearly change the carotenoid content in juice sacs. Under an ethylene-free atmosphere, differences in the gene expression profile among the temperatures were observed but were not well-correlated with those in the carotenoid content in flavedo and juice sacs. Under an ethylene atmosphere, in flavedo, the gene expression of phytoene synthase (PSY) and phytoene desaturase (PDS) was slightly higher at 20 degrees C but lower at 5 degrees C than under an ethylene-free atmosphere. At 20 degrees C, the gene expression of several carotenoid biosynthetic enzymes promoted by ethylene seemed to be responsible for the enhanced accumulation of carotenoid in flavedo. In contrast, at 5 degrees C, the repressed gene expression of PSY and PDS by ethylene seemed to be primarily responsible for the repressed accumulation of carotenoid in flavedo. In juice sacs, the small response of the gene expression to ethylene seemed to be responsible for small changes in carotenoid accumulation under an ethylene atmosphere.

Homobimetallic Ruthenium Vinylidene, Allenylidene, and Indenylidene Complexes: Synthesis, Characterization, and Catalytic Studies

Abstractmagnified imageFour homobimetallic ruthenium‐(p‐cymene) complexes bearing a tricyclohexylphosphine ligand and polyunsaturated carbon‐rich fragments were obtained via a vinylidene‐allenylidene‐indenylidene cascade pathway from the ethylene complex [(p‐cymene)Ru(μ‐Cl)3RuCl(PCy3)(η2‐C2H4)] (7a). All the products were isolated and fully characterized by IR and NMR spectroscopies. The molecular structure of the indenylidene complex 11 was determined by X‐ray crystallographic analysis. The catalytic activity of the four complexes was probed in various types of olefin metathesis reactions and compared with those of a related homobimetallic ruthenium‐benzylidene complex, as well as first, second, and third generation monometallic Grubbs catalysts. In the ring‐closing metathesis (RCM) of diethyl diallylmalonate, the homobimetallic ruthenium‐indenylidene complex 11 outperformed all the ruthenium‐benzylidene complexes under investigation and was only slightly less efficient than its monometallic parent. Cross‐metathesis experiments with ethylene showed that deactivation of ruthenium‐benzylidene or indenylidene complexes was due to the rapid bimolecular decomposition of methylidene active species into ethylene complex 7a. Vinylidene and allenylidene complexes were far less efficient catalyst precursors for ring‐opening metathesis polymerization (ROMP) or RCM and remained inert under an ethylene atmosphere. Their catalytic activity was, however, substantially enhanced upon addition of an acidic co‐catalyst that most likely promoted their in situ transformation into indenylidene species. Due to its straightforward synthesis and high metathetical activity, homobimetallic ruthenium‐indenylidene complex 11 is a valuable intermediate for the preparation of the Hoveyda–Grubbs catalyst [Cl2Ru(PCy3)(CH‐o‐O‐i‐PrC6H4)] via stoichiometric cross‐metathesis with 2‐isopropoxystyrene. The procedure did not require any sacrificial phosphine and the transition metal not incorporated into the final product was easily recovered and recycled at the end of the process.

Acceleration Effect of an Allylic Hydroxy Group on Ring‐Closing Enyne Metathesis of Terminal Alkynes: Scope, Application, and Mechanistic Insights

An interesting acceleration effect of an allylic hydroxy group on ring-closing enyne metathesis has been found. Ring-closing enyne metathesis of terminal alkynes possessing an allylic hydroxy group proceeded smoothly without the ethylene atmosphere generally necessary to promote the reaction. The synthesis of (+)-isofagomine with the aid of this efficient reaction has been demonstrated. Mechanistic studies of the acceleration effect were also carried out. Results of NMR studies suggested that the reaction proceeded via an "ene-then-yne" pathway. Kinetic studies indicated switching of the rate-determining step as a consequence of the presence of an allylic hydroxy group. These results suggest acceleration of the reentry step of Ru-carbene species by the allylic hydroxy group.

Ruthenium-Catalyzed Alkenylative Cyclization via Insertion of Alkene into Ruthenacyclopentene

A novel ruthenium-catalyzed alkenylative cyclization of enyne was developed. When an enyne was reacted with Cp*RuCl(cod) under an atmosphere of ethylene, ethylene was inserted into the ruthenium−sp2 carbon bond of ruthenacyclopentene derived from enyne and the low-valent ruthenium complex to afford ruthenacycloheptene, and β-hydrogen elimination followed by reductive elimination occurred to give a cyclic compound having a diene moiety. In this reaction, acrylaldehyde could be inserted into ruthenacyclopentene instead of ethylene. Various carbo- and heterocyclic compounds could be obtained in high yields.

Total Synthesis of Aburatubolactam A

Total Synthesis of Aburatubolactam A

Metallocene Combinations in Ethylene Polymerization: A Cyclic and Differential Pulse Voltammetry Study

A series of metallocenes, namely [Cp 2 ZrCl 2 ], [(MeCp) 2 ZrCl 2 ], [(nBuCp) 2 ZrCl 2 ], [(iBucp) 2 ZrCl 2 ], [(tBuCp) 2 ZrCl 2 ] , [Cp 2 TiCl 2 ], [Et(Ind) 2 ZrCl 2 ], [Et(IndH 4 ) 2 ZrCl 2 ] and [Mesi 2 (Ind) 2 ZrCl 2 )], were combined in a 1:1 molar ratio within a reactor for ethylene polymerization, with MAO as the cocatalyst. The catalysts were characterized by cyclic and differential pulse voltammetry. The combined systems that showed the highest and lowest activities were combined in 1:3 and 3:1 molar ratios. The catalyst activity in the ethylene polymerization reaction is discussed in terms of the estimated consumption rate, decomposition rate constant and half-life of the metallocene species formed with MAO in an ethylene atmosphere.

Acceleration effect of allylic hydroxy group on ring-closing enyne metathesis of terminal alkynes: scope and application to the synthesis of isofagomine

An interesting allylic substituent effect on ring-closing enyne metathesis has been found. An allylic hydroxy group on enyne substrates accelerates ring-closing enyne metathesis of terminal alkynes. The reaction proceeds smoothly without ethylene atmosphere and/or more reactive newer generation Ru-carbene catalysts, which are generally necessary to promote the reaction. This efficient reaction was applied to the synthesis of isofagomine.