- A novel copper(ii) complex with an unsymmetrical tridentate-Schiff base: synthesis, crystal structure, electrochemical, morphological and electrocatalytic behaviors toward electroreduction of alkyl and aryl halides
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This work describes the synthesis of a new unsymmetrical tetradentate copper(ii) Schiff base complex Cu(L)(Py)(ClO4) containing N3O donor atoms. The tridentate ligand (HL) has been prepared by condensation of dehydroacetic acid on 1,2-diaminopropane in methanol. The reaction of the ligand with an appropriate amount of copper(ii) perchlorate hexahydrate (1 : 1 ratio) in the same solvent and in the presence of an excess of pyridine (Py) yields the title compound. The tridentate ligand (HL) with pyridine act as mixed ligands where three nitrogen and an enolic oxygen atoms were chelated to the copper centre. This complex has been fully characterized by FT-IR, UV-Vis spectrophotometry, and cyclic voltammetry. Single crystal X-ray diffraction of this complex showed that the copper ion was coordinated by one ligand, one pyridine molecule with one perchlorate anion in a square pyramidal geometry. The Cu(L)(Py)(ClO4) complex crystallizes in an orthorhombic system, space group of Pcab with a = 11.051, b = 15.58, c = 21.736 ? and Z = 8. The electrochemical reduction of the copper(ii) complex, in N,N-dimethylformamide (DMF) solvent using cyclic voltammetry, produces conducting polymeric films on different electrode substrates, such as glassy carbon (GC), indium tin oxide (ITO) and fluorine tin oxide (FTO). The catalytic activity of this complex in homogeneous and heterogeneous electrocatalytic media seems to be efficient for the electroreduction of bromocyclopentane and iodobenzene.
- Ourari, Ali,Derafa, Wassila,Aggoun, Djouhra
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- Photoredox-Assisted Reductive Cross-Coupling: Mechanistic Insight into Catalytic Aryl-Alkyl Cross-Couplings
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Here, we describe a photoredox-assisted catalytic system for the direct reductive coupling of two carbon electrophiles. Recent advances have shown that nickel catalysts are active toward the coupling of sp3-carbon electrophiles and that well-controlled, light-driven coupling systems are possible. Our system, composed of a nickel catalyst, an iridium photosensitizer, and an amine electron donor, is capable of coupling halocarbons with high yields. Spectroscopic studies support a mechanism where under visible light irradiation the Ir photosensitizer in conjunction with triethanolamine are capable of reducing a nickel catalyst and activating the catalyst toward cross-coupling of carbon electrophiles. The synthetic methodology developed here operates at low 1 mol % catalyst and photosensitizer loadings. The catalytic system also operates without reaction additives such as inorganic salts or bases. A general and effective sp2-sp3 cross-coupling scheme has been achieved that exhibits tolerance to a wide array of functional groups.
- Paul, Avishek,Smith, Mark D.,Vannucci, Aaron K.
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supporting information
p. 1996 - 2003
(2017/02/26)
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- Hydrodeoxygenation of Fatty Acids, Triglycerides, and Ketones to Liquid Alkanes by a Pt–MoOx/TiO2 Catalyst
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Various supported metal catalysts are screened for hydrogenation of lauric acid and 2-octanone as model reactions for the transformation of biomass-derived oxygenates to liquid alkanes (biofuels) in a batch reactor under solvent-free conditions. Among the catalysts tested, Pt and MoOx co-loaded on TiO2 (Pt–MoOx/TiO2) shows the highest yields of n-alkanes for both of the reactions. Pt–MoOx/TiO2 selectively catalyzes the hydrodeoxygenation of various fatty acids and triglycerides to n-alkanes without C?C bond cleavage under 50 bar H2 and shows higher turnover numbers than the catalysts in the literature. Pt–MoOx/TiO2 is effective also for the hydrodeoxygenation of various ketones to the corresponding alkanes. In situ IR study of the reaction of adsorbed acetone under H2 suggests that the high activity of Pt–MoOx/TiO2 is attributed to the cooperation between Pt and Lewis acid sites of the MoOx/TiO2 support.
- Kon, Kenichi,Toyao, Takashi,Onodera, Wataru,Siddiki,Shimizu, Ken-Ichi
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p. 2822 - 2827
(2017/07/28)
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- Highly selective self-condensation of cyclic ketones using MOF-encapsulating phosphotungstic acid for renewable high-density fuel
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Transferring biomass-derived cyclic ketones such as cyclopentanone and cyclohexanone to a mono-condensed product through aldol self-condensation has great potential for the synthesis of a renewable high-density fuel. However, the selectivity is low for numerous catalysts due to the rapid formation of di-condensed by products. Herein, MIL-101-encapsulating phosphotungstic acid is synthesized to catalyze the self-condensation with selectivity of more than 95%. PTA clusters are uniformly dispersed in MOF cages and decrease the empty space (pore size), which provides both acidic sites and shape-selective capability. The optimal PTA amount decreases corresponding to the increase of reactant size. The shape-selectivity is also realized by changing the pore size of MOF such as from MIL-101 to MIL-100. Moreover, the catalyst is resistant to PTA leaching and performs stably after 5 runs. After hydrodeoxygenation of the mono-condensed product, high-density biofuels with densities of 0.867 g ml-1 and 0.887 g ml-1 were obtained from cyclopentanone and cyclohexanone, respectively. This study not only provides a promising route for the production of high-density biofuel but also suggests the advantage of MOF-based catalysts for shape-selective catalysis involving large molecular size.
- Deng, Qiang,Nie, Genkuo,Pan, Lun,Zou, Ji-Jun,Zhang, Xiangwen,Wang, Li
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p. 4473 - 4481
(2015/08/11)
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- Synthesis of renewable high-density fuels using cyclopentanone derived from lignocellulose
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By the combination of solvent-free aldol condensation and one-step hydrodeoxygenation under mild reaction conditions, a high-density (0.866 g mL-1) bicyclic C10 hydrocarbon was synthesized in high overall yield (up to 80%) using cyclopentanone derived from lignocellulose. The Royal Society of Chemistry 2014.
- Yang, Jinfan,Li, Ning,Li, Guangyi,Wang, Wentao,Wang, Aiqin,Wang, Xiaodong,Cong, Yu,Zhang, Tao
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supporting information
p. 2572 - 2574
(2014/03/21)
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- Reductive dimerization and oligomerization of alcohols, ketones, and aldehydes to hydrocarbons on a promoted, fused iron catalyst
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A new reductive dimerization and oligomerization reaction of (C5 and C6) cycloalkanols and cycloalkanones, benzaldehyde, and benzyl alcohol to hydrocarbons containing as many, or more, carbon atoms as the reactant oxygenated compound on a promoted, fused iron catalyst proceeds at a temperature of 250-350°C, a hydrogen pressure of 0.1-1 MPa, a specific feed rate of oxygenated reagent of 80-320 g h-1kg-1Ct, and a hydrogen space velocity of 1 × 103 to 20 × 103 h-1. Possible reaction mechanisms have been considered.
- Glebov,Zaikin,Mikaya,Kliger
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p. 296 - 308
(2014/08/05)
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- Ni-catalyzed reductive homocoupling of unactivated alkyl bromides at room temperature and its synthetic application
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A room-temperature Ni-catalyzed reductive approach to homocoupling of unactivated primary, secondary, and tertiary alkyl bromides is described. The catalytic system can be easily generated from air-stable and cheap materials and demonstrates broad functional group tolerance, thus allowing facile access to useful dimeric triterpene and lignan-like molecules. Moreover, the dimerization of tertiary bromide 6 efficiently establishes sterically hindered vicinal quaternary carbons (C3a and C3a′), which is a key linkage of intriguing bispyrrolo[2,3-b]indoline alkaloids, thereby enabling us to complete the total syntheses of racemic chimonanthine (9) and folicanthine (10). In addition, this dimerization method can be expanded to the highly stereoselective synthesis of bisperhydrofuro[2,3-b]furan (5a) and the dimeric spiroketal 5b, signifying the involvement of possible radical species.
- Peng, Yu,Luo, Long,Yan, Chang-Song,Zhang, Jian-Jian,Wang, Ya-Wen
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p. 10960 - 10967
(2013/11/19)
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- Conversion of furfural into cyclopentanone over Ni-Cu bimetallic catalysts
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The conversion of furfural into cyclopentanone over Ni-Cu bimetallic catalysts was studied under hydrogen atmosphere. Furfuryl alcohol, 4-hydroxy-2-cyclopentenone and 2-cyclopentenone were verified as three key intermediates. Rearrangement of the furan ring was independent of hydrogenation, starting from furfuryl alcohol rather than furfural. The opening and closure of the furan ring were closely related to the attack of a H2O molecule on the 5-position of furfuryl alcohol. Prior hydrogenation of the aldehyde group accounted for the different reactivity of furfural and furfuryl alcohol. The high selectivity of cyclopentanone was ascribed to the presence of 2-cyclopentenone.
- Yang, Yanliang,Du, Zhongtian,Huang, Yizheng,Lu, Fang,Wang, Feng,Gao, Jin,Xu, Jie
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supporting information
p. 1932 - 1940
(2013/09/24)
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- Replacing conventional carbon nucleophiles with electrophiles: Nickel-catalyzed reductive alkylation of aryl bromides and chlorides
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A general method is presented for the synthesis of alkylated arenes by the chemoselective combination of two electrophilic carbons. Under the optimized conditions, a variety of aryl and vinyl bromides are reductively coupled with alkyl bromides in high yields. Under similar conditions, activated aryl chlorides can also be coupled with bromoalkanes. The protocols are highly functional-group tolerant (-OH, -NHTs, -OAc, -OTs, -OTf, -COMe, -NHBoc, -NHCbz, -CN, -SO2Me), and the reactions are assembled on the benchtop with no special precautions to exclude air or moisture. The reaction displays different chemoselectivity than conventional cross-coupling reactions, such as the Suzuki-Miyaura, Stille, and Hiyama-Denmark reactions. Substrates bearing both an electrophilic and nucleophilic carbon result in selective coupling at the electrophilic carbon (R-X) and no reaction at the nucleophilic carbon (R-[M]) for organoboron (-Bpin), organotin (-SnMe3), and organosilicon (-SiMe2OH) containing organic halides (X-R-[M]). A Hammett study showed a linear correlation of σ and σ(-) parameters with the relative rate of reaction of substituted aryl bromides with bromoalkanes. The small ρ values for these correlations (1.2-1.7) indicate that oxidative addition of the bromoarene is not the turnover-frequency determining step. The rate of reaction has a positive dependence on the concentration of alkyl bromide and catalyst, no dependence upon the amount of zinc (reducing agent), and an inverse dependence upon aryl halide concentration. These results and studies with an organic reductant (TDAE) argue against the intermediacy of organozinc reagents.
- Everson, Daniel A.,Jones, Brittany A.,Weix, Daniel J.
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supporting information; experimental part
p. 6146 - 6159
(2012/05/07)
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- A structure-activity study of Ni-catalyzed alkyl-alkyl kumada coupling. Improved catalysts for coupling of secondary alkyl halides
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A structureactivity study was carried out for Ni catalyzed alkylalkyl Kumada-type cross coupling reactions. A series of new nickel(II) complexes including those with tridentate pincer bis(amino)amide ligands (RN2N) and those with bidentate mixed amino-amide ligands (RNN) were synthesized and structurally characterized. The coordination geometries of these complexes range from square planar, tetrahedral, to square pyramidal. The complexes had been examined as precatalysts for cross coupling of nonactivated alkyl halides, particularly secondary alkyl iodides, with alkyl Grignard reagents. Comparison was made to the results obtained with the previously reported Ni pincer complex [( MeN2N)NiCl]. A transmetalation site in the precatalysts is necessary for the catalysis. The coordination geometries and spin-states of the precatalysts have a small or no influence. The work led to the discovery of several well-defined Ni catalysts that are significantly more active and efficient than the pincer complex [(MeN2N)NiCl] for the coupling of secondary alkyl halides. The best two catalysts are [(HNN)Ni(PPh3)Cl] and [(HNN)Ni(2,4-lutidine)Cl]. The improved activity and efficiency was attributed to the fact that phosphine and lutidine ligands in these complexes can dissociate from the Ni center during catalysis. The activation of alkyl halides was shown to proceed via a radical mechanism.
- Ren, Peng,Vechorkin, Oleg,Von Allmen, Kim,Scopelliti, Rosario,Hu, Xile
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supporting information; experimental part
p. 7084 - 7095
(2011/06/26)
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- Thiotolerant Ir/SiO2-Al2O3 bifunctional catalysts: Effect of metal-acid site balance on tetralin hydroconversion
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The hydroconversion of tetralin over iridium nanoparticles supported on amorphous silica-alumina (ASA) has been investigated in a continuous high-pressure gas-phase micro-reactor in the presence of H2S. In order to tune the Ir particle size, the bifunctional Ir/ASA catalysts have been submitted to sintering treatments. The samples have been characterized by HRTEM and XPS. From careful analysis of tetralin conversion products by comprehensive two-dimensional gas chromatography (GC×GC-MS) and NMR, compound families have been unambiguously distinguished. Hydrogenation, dehydrogenation, (saturated and aromatic) ring-contraction products, and (saturated and aromatic) one-ring-opening products are formed, without significant cracking. The catalysts exhibit stable activity in the presence of sulfur. As the mean particle size increases from 1.5 to 8 nm, the ring-opening/contraction selectivity increases dramatically. This effect is related to an increase of the acid/metal site ratio.
- Nassreddine, Salim,Massin, Laurence,Aouine, Mimoun,Geantet, Christophe,Piccolo, Laurent
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scheme or table
p. 253 - 265
(2011/04/22)
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- Nickel-catalyzed, sodium iodide-promoted reductive dimerization of alkyl halides, alkyl pseudohalides, and allylic acetates
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The first general method for the reductive dimerization of alkyl halides, alkyl mesylates, alkyl trifluoroacetates, and allylic acetates is reported which proceeds with low catalyst loading (0.5 to 5 mol%), generally high yields (80% ave yield), and good functional-group tolerance.
- Prinsell, Michael R.,Everson, Daniel A.,Weix, Daniel J.
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supporting information; experimental part
p. 5743 - 5745
(2010/09/18)
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- Process for hydrogenation of carboxylic acids and derivatives to hydrocarbons
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A process for hydrogenating a carboxylic acid and/or derivative thereof having a carboxylate group represented by the general formula R1COO-, which process comprises feeding hydrogen and the carboxylic acid and/or derivative thereof to a reactor and maintaining conditions within the reactor such that hydrogen reacts with the carboxylic acid and/or derivative thereof to produce a product stream comprising carbon dioxide, carbon monoxide, methane and hydrocarbons represented by general formulae R1H and R1CH3, characterised in that the molar ratio of R1H : R1CH3 is above a pre-determined value and/or the mole ratio of the sum of carbon dioxide, carbon monoxide and methane to carboxylate groups is above a pre-determined value.
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Page/Page column 7-8
(2008/06/13)
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- Radical reactions in the radiolysis of cyclopentane
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The end products produced in the γ-radiolysis of cyclopentane have been measured at very low total doses (25-50 krad). Iodine scavenging techniques in solutions of 0.1-30 mM were used to elucidate radical yields and reaction mechanisms. The yields of the main radical species were found to be as follows: cyclopentyl, 4.9; 1-pentyl, 0.2; 3-cyclopentenyl, 0.07; H atom, 1.3 radical/100 eV. The change in yields from neat cyclopentane to 0.1 mM iodine solution suggests that about 79% of the cyclopentyl radicals escape the spur and react in the bulk medium with a disproportionation to combination ratio of 0.97. Radical precursors account for about 50% of the total end product yield, which is much smaller than found in the radiolysis of cyclohexane or cyclooctane. The radiolysis mechanism for cyclopentane is discussed and compared to those for cyclohexane and cyclooctane.
- Wojnarovits,LaVerne
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p. 3168 - 3172
(2007/10/02)
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- Heavy ion radiolysis of cyclopentane
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The radiolysis of neat and iodine solutions of cyclopentane has been performed with 1-15 MeV protons, 5-20 MeV helium ions, 12-31 MeV carbon ions, and 22-32 MeV oxygen ions. The yields of the major products cyclopentene, bicyclopentyl, 1-pentene, and cyclopentyl iodide as well as the yields of a few select minor products have been determined. All products show a decrease in yield with increasing linear energy transfer (LET) of the irradiating particle. Some of these decreases are very large: for instance, the observed drop in the yield of bicyclopentyl from γ-rays (LET = 0.14 eV/nm) to oxygen ions (LET = 900 eV/nm) amounts to a net loss of about 4 cyclopentyl radicals/100 eV absorbed energy. This value is 80% of the total cyclopentyl radicals produced in γ-radiolysis. There are some indications that the yields of radicals due to decomposition of excited cyclopentane molecules are dependent on the energy and type of irradiating particle.
- Wojnarovits,La Verne
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p. 11292 - 11296
(2007/10/02)
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- On the Mechanism of the Benzophenone-Sensitized Photolysis of 2,3-Diazabicyclohept-2-ene in the Laser Jet: Evidence for Intermolecular Triplet Diradical Reactions
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The benzophenone-sensitized laser jet photolysis of 2,3-diazabicyclohept-2-ene (1) affords, besides the previously reported cyclopentene and housane (2), also cyclopentane, cyclopentadiene, and the dimers bicyclopent-2-en-1-yl (7), 3-cyclopentylcyclopent-1-ene (8), and 1,1'-bicyclopentyl (9).As a model reaction, the pyrolysis of dimer 8 at 600 deg C/ 20 Torr leads to the other dimers 7 and 9 together with cyclopentadiene, cyclopentene, and traces of cyclopentane.Control experiments showed that H abstraction by the cyclopentane-1,3-diyl diradical (3) from cyclohexene (as model substrate for cyclopentene) and addition to housane (2) with formation of diradical 6 are unlikely pathways.Instead, the product data available can be best explained in terms of an intermolecular disproportionation of two diradicals 3 to give the cyclopent-2-en-1-yl (4) and cyclopentyl (5) radical pair, which is subsequently converted to the observed products by in-cage and out-of-cage coupling and H transfer reactions.Such intermolecular diradical chemistry becomes feasible due to the high steady-state concentrations (ca. micromolar) generated in the laser jet.Two-photon processes take place, but are of subordinate importance. - Key Words: Laser jet/ Azoalkane/ Diradical/ Radical coupling
- Adam, Waldemar,Finzel, Ralf,Walther, Barbara
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p. 2137 - 2142
(2007/10/02)
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- Carbenes and the O-H bond: Bicycloalkylidenes
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Photolyses of spirobicyclic diazirines in alcohols have been investigated in order to elucidate the insertion reactions of bicycloalkylidenes with O-H bonds. The formation of ethers from norbornane-derived diazirines (16 and 30) was traced to the intervention of diazo compounds which react by way of diazonium ions. Scavenging of the diazo compounds with potent dipolarophiles led to almost exclusive formation of nortricyclenes from 2-norbornylidenes (17 and 32). In contrast, 2-bieyclo[2,1.1]hexylidene (45) was found to undergo intermolecular reactions, including addition to alkenes and C-H insertion with cycloalkanes. When alcoholic solutions of bicyclo[2.1.1]hexane-derived diazirines (41, 58, 73, and 76) were irradiated, diazo scavengers did not eliminate the formation of ethers. By means of deuterium labels or methyl groups, rearrangement and fragmentation reactions were detected that are characteristic of carbocations (ion pairs). Protonation of 2-bicyclo[2.1.1]hexylidenes by ROH is therefore implied. Laser flash photolysis studies confirmed the divergent lifetimes of 17 (0.1 ns) and 45 (50-600 ns). The reaction rate of 45 was found to increase with the acidity of the alcohols.
- Kirmse, Wolfgang,Meinert, Thomas,Modarelli, David A.,Platz, Matthew S.
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p. 8918 - 8927
(2007/10/02)
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- Soluble, highly conjugated derivatives of polyacetylene from the ring-opening metathesis polymerization of monosubstituted cyclooctatetraenes: Synthesis and the relationship between polymer structure and physical properties
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Using well-defined tungsten-based olefin metathesis catalysts, a family of partially substituted polyacetylenes have been synthesized via the ring-opening metathesis polymerization (ROMP) of monosubstituted cyclooctatetraenes (RCOT). These polymers are highly conjugated, as evidenced by their visible absorption maxima. They are of high molecular weight, as evidenced by gel permeation chromatography, and most members of the family are soluble in the as-synthesized, predominantly cis form. The polymers can be isomerized to the predominantly trans form using heat or light. The rate of thermal isomerization was monitored by visible absorption spectroscopy. Polymers containing, in general, secondary or tertiary groups immediately adjacent to the main chain remain soluble in the trans form and are, in most cases, still highly conjugated. Overall, there is a connection between the steric bulk of the side group in polymers of monosubstituted COTs, their effective conjugation length, and their solubility. The side group twists the main chain of the polymer and also induces a preference for cis units in the chain. The tradeoff between conjugation and solubility has been explored, and highly conjugated polyacetylenes that are still soluble have been discovered. In the solid state, these polymers are observed to be amorphous by wide-angle X-ray scattering and near-infrared scattering. The amorphous nature of these samples correlates with the relatively low temperature cis-trans isomerization in the solid state. Upon iodine doping, these polymers become electrically conductive, although their conductivities are smaller than those of unsubstituted polyacetylene. Both empirical and semiempirical computational methods indicate an increased preference for cis linkages in partially substituted polyacetylene chains and show twists around the single bonds adjacent to the side groups in the polymer chain. The relative magnitude of these twists can be used to rationalize the differences in solubilities of the various polyacetylene derivatives, and these models provide a means of visualizing the conformation of the polymer, at least on its smallest size regime. The computations have also been useful in the rational design of new soluble polyacetylene derivatives with high effective conjugation lengths. By modeling and then synthesizing chains containing sec-butyl and other secondary groups, these properties have been realized.
- Gorman, Christopher B.,Ginsburg, Eric J.,Grubbs, Robert H.
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p. 1397 - 1409
(2007/10/02)
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- Making Mercury-Ptotosensitized Dehydrodimerization into an Organic Synthetic Method: Vapor Pressure Selectivity and the Behavior of Functionalized Substrates
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Mercury-photosensitized dehydrodimerization in the vapor phase can be made synthetically useful by taking advantage of a simple reflux apparatus (Figure 1), in which the products promptly condense and are protected from further conversion.This vapor pressure selectivity gives high chemical selectivity even at high conversion and on a multigram scale.Mercury absorbs 254-nm light to give the 3P1 excited state (Hg*), which homolyses a C-H bond of the substrate with a 3o>2o>1o selectivity.Quantitative prediction of product mixtures in alkane dimerization and in alkane-alkane cross-dimerizations is discussed.Radical disproportionation gives alkene, but this intermediate is recycled back into the radical pool via H atom attack, which is beneficial both for yield and selectivity.The method is very efficient at constructing C-C bonds between highly substituted carbon atoms, yet the method fails if a dimer has four sets of obligatory 1,3-syn methyl-methyl steric repulsions, as in the unknown 2,3,4,4,5,5,6,7-octamethyloctane.We have extended the range of substrates susceptible to the reaction, for example to higher alcohols, ethers, silanes, partially fluorinated alcohols, and partially fluorinated ethers.We see selectivity for dimers involving C-H bonds α to O or N and for S-H over C-H.An important advantage of our experimental conditions in the case of alcohols is that the aldehyde or ketone disproportionation product (which is not subject to H. attack) is swept out of the system by the stream of H2 also produced, so it does not remain and inhibit the rate and lower the selectivity. kdis/krec is estimated for a number of radicals studied.The very hindered 3o 1,4-dimethylcyclohex-1-yl radical is notable in having a kdis/krec as high as 7.1.
- Brown, Stephen H.,Crabtree, Robert H.
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p. 2935 - 2946
(2007/10/02)
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- Alkane Functionalization on a Preparative Scale by Mercury-Photosensitized Cross-Dehydrodimerization
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Alkanes can be functionalized with high conversions and in high chemical and quantum yields on a multigram scale by mercury-photosensitized reaction between an alkane and alcohols, ethers, or silanes to give homodimers and cross-dehydrodimers.The separation of the product mixtures is often particulary easy because of a great difference in polarity of the homodimers and cross-dimers.It is also possible to bias the product composition when the ratio of the components in the vapor phase is adjusted by altering the liquid composition.This is useful either to maximize chemical yield or to ease separation by favoring the formation of the most easily separated pair of compounds.The mechanistic basis of the reaction is discussed and a number of specific types of syntheses, for example of 2,2-disubstituted carbinols, are described in detail.The selectivity of cross-dimerization is shown to exceed that for homodimerization and reasons are discussed.Relative reactivities of different compounds and classes of compound are MeOHp-dioxanecyclohexane1,3,5-trioxacyclohexaneethanolisobutaneTHFEt3SiH.The observed selectivities generally parallel those for homodimerization, reported in the preceding paper, but certain differences are noted, and reasons for the differences are proposed.The bond-dissociation energy of Et3SiH is estimated from the reactivity data to be 90 kcal/mol.Eleven new carbinols are synthesized.
- Brown, Stephen H.,Crabtree, Robert H.
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p. 2946 - 2953
(2007/10/02)
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- On the Rearrangement of a Tricyclic Unsaturated Ketone during Wolff-Kishner Reduction
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Wolff-Kishner reduction of tricyclo2,5>dec-3-en-9-one (1) yields only 2-9percent of the expected olefin 7, 1-3percent of the syn isomer 8, but 17-26percent of bi(1-cyclopentenyl) (5).
- Otterbach, Andreas,Musso, Hans
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p. 2257 - 2258
(2007/10/02)
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- Substituent Effects on Hydrogen Abstraction by Phenyl Ketone Triplets
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Triplet lifetimes in deaerated cyclopentane have been measured for a variety of ring-substituted benzophenones, acetophenones, and α-α-α-trifluoroacetophenones.The ketones undergo photoreduction under these conditions to mixtures of products formed from cyclopentyl and hemipinacol radicals.That triplet lifetimes are determined by rates of hydrogen abstraction from solvent is indicated by lifetimes being three times in cyclohexane-d12 than in cyclohexane-h12.For the benzophenones, reciprocal lifetimes correlate comparably well with Hammett ? or ?+ constants, with ρ values of 0.55 and 0.43, respectively.The effect of two substituentsis best fitted to the sum of both ? values.These weak inductive effects are in accord with expectations for a reactive n,?* triplet.Rates for the acetophenones show the same substituent effects as previously observed for valerophenones; conjugating and electron-donating substituents stabilize the ?,?* triplet and sharply reduce reactivity.Substituent effects are largest for the trifluoroacetophenones, consistent with their all having ?,?* lowest triplets and reacting from weakly populated but highly reactive (k>107 M-1 s-1) n,?* states.Fluorine substitution, both on the ring and at the α-carbon, produces large rate enhancements, decafluorobenzophenone triplet being too short-lived to measure.
- Wagner, Peter J.,Truman, Royal J.,Scaiano, J. C.
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p. 7093 - 7097
(2007/10/02)
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- Selective Formation of Solute Radicals in the Radiolysis of Neopentane-Cyclopentane Mixtures at 4 and 77 K as Studied by Capillary Gas Chromatography and ESR Spectroscopy
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The dimer yields in the radiolysis of the neo-C5H12-cyclo-C5H11 (1 molpercent) mixtures at 77 and 4 K have been measured by capillary gas chromatography.Analysis of the results indicates that cyclopentyl radicals are produced selectively at 77K, while their selective formation is suppressed at 4K.This result coincides well with the data obtained by ESR spectroscopy.
- Tilquin, Bernard,Gourdin-Serveniere, Catherine,Miyazaki, Tetsuo,Fueki, Kenji
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p. 2029 - 2030
(2007/10/02)
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- Anodic Oxidation of Organoboranes
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Organoboranes are converted into more easily oxidizable borates by reaction with nucleophiles and the alkyl groups are dimerized by anodic oxidation.The oxidation potentials (Ep) of the borates depend strongly on the nature of the complexing nucleophile, for instance Ep = +0.37 V (vs.SCE) with OH- or +1.65 V with tetrahydrofuran.The dimer yields are optimized with trioctylborane (5) by variation of the electrode material and the elctrolyte.At the platinum anode in sodium hydroxide-methanol/tetrahydrofuran yields of 80percent are obtained for acyclic alkyl groups, and lo wer ones for cycloalkyl groups.They exceed those obtained by the Kolbe electrolysis or the oxidation with neutral hydrogen peroxide and they are comparable to those of the AgNO3 oxidation. - The selective preparation of unsymmetrical products from borates with different alkyl groups is not possible, the dimerization proceeds likely via free radicals that couple statistically.Good yields of unsymmetrical coupling products are achieved, when one olefin is used in excess.With choro-, ethoxy-, acetoxy-, and aryl-substituted alkyl groups the dimers are obtained in 21 - 66percent yield, with bromide the yield are lower and with nitriles the dimerization fails.
- Schlegel, Guenter,Schaefer, Hans J.
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p. 1400 - 1423
(2007/10/02)
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- DECOMPOSITION DU PERCARBONATE DE O,O-t-BUTYLE ET O-ISOPROPENYLE EN SOLUTION DANS DES CYCLANES
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Thermolysis of O,O-t-butyl and O-isopropenyl percarbonate in cyclohexane involves free-radical acetonylation of solvent.Free radicals derived from solvent add to the percarbonate double bond and after a double β-scission reaction, cyclohexylacetone carbon dioxide and t-butoxy radicals are formed.Abstracting H atoms from the solvent, t-butoxy radicals regenerate free radicals from solvent, and the reaction becomes a chain process.Extending the study to other cycloalkanes it has been shown that the process is a general synthesis method for cycloalkylacetones.On the other hand, competitive reactions of pairs of solvents have shown that the reactivity of the substrates depends on H atom lability and on more complex phenomena like transfers between hydrocarbons and C-centred free-radicals.
- Jaouhari, R.,Filliatre, C.,Maillard, B.,Villenave, J.J.
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p. 3137 - 3142
(2007/10/02)
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- Transition Metal Activated Organic Compounds, XI. Connection of Saturated Six-membered Ring Systems at C- or N-Atoms via Copper Compounds
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The CC-coupling of alkyl- or NN-coupling of dialkylamino groups via copper compounds is, as a rule, disturbed or thwarted by β-elimination of a copper hydride species.This disturbing reaction, especially effective with dialkylamino groups, is strongly diminished with saturated six-membered rings which undergo coupling in preparatively useful yields.The oxygen atom in the dialkylamine morpholine as an additional coordination center completely suppresses the copper hydride elimination, thus only coupling is observed.
- Jackisch, Joerg,Legler, Jochen,Kauffmann, Thomas
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p. 659 - 668
(2007/10/02)
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- Mechanism of Formation of Grignard Reagents. Rate of Reaction of Cyclopentyl Bromide with a Rotating Disk of Magnesium
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Careful studies of the dependence of the rate of reaction (k) of cyclopentyl bromide in diethyl ether with the surface of rotating disk as a function of the angular lelocity (ω) of the disk confirm the relation k * ω1/2 expected for a mass-transfer limited reaction.More limited studies also indicate that the variations in this rate with other parameters are compatible with those expected for a mass-transfer limited reaction: k * (η)-5/6(ρ)1/6 (η is the shear viscosity of the solution and ρ is its density); k * D2/3 (D is the diffusion coefficient of the alkyl halide).
- Root, Karen S.,Deutch, John,Whitesides, George M.
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p. 5475 - 5479
(2007/10/02)
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- On the Oligomerization of Cyclic Alkenes in the Presence of Zirconium-containing Catalytic Systems
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In connection with investigations on olefin metathesis we studied the reaction of cyclic olefins C5 - C8 and C12 in the presence of zirconium-containing catalytic systems in the homogeneous liquid phase.The influence of different zirconium compounds on the reaction run off and on the distribution of the reaction products was examined in the presence and the absence of Lewis acids.The reaction products could be separated and identified by a combination of distillation, chromatographical, chemical and spectrometrical methods.The results show that under the conditions mentioned a metathetic polymerization and a normal olefin oligomerization take place simultaneously.
- Bittrich, H.-H.,Bittrich, R.,Sass, L.,Zirz, P.,Reich, P.,Zimmermann, G.
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p. 177 - 187
(2007/10/02)
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- UNIMOLECULAR H2 ELIMINATION DURING THE LIQUID PHASE RADIOLYSIS AND PHOTOLYSIS OF ALKANE-ALKANE MIXTURES
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Unimolecular H2 elimination from alkanes was investigated in cyclopentane-cyclohexane, n-hexane-cyclohexane and cyclohexane-cyclooctane mixtures during radiolysis and 7.6 eV photolysis.During the radiolysis of all system, and when the fluorescence shift law allowed it, during the photolysis as well, inhibited H2 detachment was observed from the first component and sensitized hydrogen molecule elimination from the second.It has been concluded that the same excited state (the lowest singlet, S1) is responsible for the H2 elimination during radiolysis and photolysis and this is that one that gives rise to fluorescence in the experiments of other authors.The H2 and H elimination from alkanes generally have different excited precursors.The direct population of S1 by γ-irradiation is of limited importance and this intermediate is mainly produced in "charge neutralization" processes.
- Wojnarovits, L.,Foeldiak, G.
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- Mechanism of Formation of Grignard Reagents. The Rate of Reaction of Cyclopentyl Bromide with Magnesium Is Transport Limited in Diethyl Ether
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Three observations indicate that the rate of reaction of cyclopentyl bromide with metallic magnesium in several ethereal solvents is limited by the rate of its encounter with the metal.First, the rate of disappearance of cyclopentyl bromide is dependent on the first power of the organic halide concentration, the magnesium surface area, and rate at which the solution is stirred, and is inversely dependent on the solution viscosity (-d/dt infinite 1, A1, ω1, η-1).Second, the activation energy for the reaction in diethyl ether (Ea ca. 2.3 kcal/mol) is consistent with mixing and diffusion as rate limiting.Third, a number of representative alkyl halides react with magnesium in diethyl ether at very similar rates; no organic halides examined react faster than this rate.The dependence of the rate of reaction of neopentyl bromide on solution dielectric constant illustrates transition from transport-limited to non-transport-limited rates, and suggests appreciable charge separation in the chemical step which breaks the carbo-bromine bond.
- Rogers, Harold R.,Deutch, John,Whitesides, George M.
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p. 226 - 231
(2007/10/02)
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