20237-34-7Relevant academic research and scientific papers
Applications of PC(sp3)P iridium complexes in transfer dehydrogenation of alkanes
Bzier, David,Brookhart, Maurice
, p. 3411 - 3420 (2015/02/19)
Iridium ethylene complexes based on the PC(sp3)P pincer-type triptycene ligand have been synthesized. Complexes bearing various substituents on the phosphines have been investigated as catalysts in transfer dehydrogenation of alkanes. The complex 8a, which bears isopropyl groups, has demonstrated high stability and activity when used as a catalyst in the disproportionation of 1-hexene at 180 °C and in the transfer dehydrogenation of linear and cyclic alkanes with tert-butylethylene as a hydrogen acceptor at 200°C. A similar complex bearing a CH2NMe2 group, 33, allowed support of the catalyst on γ-alumina for operation in a heterogeneous mode.
Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
, p. 402 - 415 (2007/10/03)
Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
Reactivity of unsaturated linear C6 hydrocarbons on Pd(111) and H(D)/Pd(111)
Vasquez Jr., Natividad,Madix
, p. 234 - 252 (2007/10/03)
The adsorption and reactivity of 1-hexene, 1,5-hexadiene, 1,3-hexadiene, and 1,3,5-hexatriene on clean Pd(111) and hydrogen (deuterium)-saturated/Pd(111) were investigated using temperature-programmed reaction spectroscopy. The low-temperature adsorption configuration for the linear C6 hydrocarbons is proposed to be a weakly π-bonded species. The adsorbed molecules first desorb molecularly with a fraction converting to a more tightly bonded half-hydrogenated state, which either β-hydride eliminates to release the alkene or dehydrogenates completely to adsorbed carbon and hydrogen. Dehydrocyclization to benzene is observed on this surface, whereas it does not occur on Pd(100). Cyclization of 1,3,5-hexatriene to benzene occurs at temperatures as low as 333 K on Pd(111). Although hydrogenation of 1,3-hexadiene adsorbed on clean Pd(111) and of 1,3-hexadiene and 1,5-hexadiene adsorbed on H/Pd(111) to hexene was observed, and hexatriene was hydrogenated to hexadiene and hexene, hydrogenation of the alkenes to hexane was not observed for any of the unsaturated species. H-D exchange into all the adsorbed alkenes was observed. The exchange reaction is proposed to occur through the reversible C-H bond formation in a half-hydrogenated intermediate.
Catalytic Hydromagnesation of 1,3-Alkadienes
Viktorov,Zubritskii
, p. 1706 - 1711 (2007/10/03)
Isopropylmagnesium chloride reacts with 1,3-alkadienes with formation of monomeric and linear and cyclic dimeric hydromagnesation products. 1,3-Alkadienes with longer and branched alkyl chains give rise to a smaller fraction of the dimeric products.
NICKEL CHLORIDE CATALYZED REARRANGEMENT OF ALLYLIC PHOSPHITES
Lu, Xiyan,Zhu, Jingyang
, p. 239 - 244 (2007/10/02)
Allylic phosphites can be rearranged to the corresponding allylic phosphonates under the catalysis of nickel chloride.Dienes and dialkyl phosphonates are formed by an elimination reaction when there is hydrogen atom at the β-position of the carbon-metal bond in the allylic intermediate.The mechanisms of these reactions are discussed.
Laser-Induced Infrared Multiphoton Isomerization Reactions of 2,4- ans 1,3-Hexadienes
Buechele, James L.,Weitz, Eric,Lewis, Frederick D.
, p. 868 - 876 (2007/10/02)
Efficient and clean isomerization has been observed in the system consisting of the conjugated 2,4- and 1,3-hexadienes following infrared multiphoton excitaton of these species.Variations of both laser fluence and pressure of the added inert gas are seen to significantly effect branching ratios and yields.Where a competition exists between a low activation energy, low preexponential factor pathway and one with a high activation energy, high preexponential factor, an increase in fluence is seen to favor the latter pathway.An estimate of the degree of excitation in the molecule is obtainable from product branching ratios and inert gas quenching behavior.Photoacoustic measurements of energy input coupled with observation of product ratios indicate that the production of multiple products in a single laser pulse is compatible with a sequential isomerization mechanism which takes place in an almost vibrationally adiabatic fashion.Thermal and CW laser studies of hexadiene isomerization have been performed.Thermal studies yield rate constants and ΔH and ΔS for the various isomers.Thermal studies coupled with multiphoton studies have helped establish the isomerization pathway connecting the cis,trans-2,4- and trans-1,3-hexadiene isomers and have confirmed the other isomerization pathway in the system.The pathways for CW cw laser-induced isomerization have been studied.
Metal Catalysis in Organic Reactions. Part 13. The Reaction of 3-En-1-ynes with Trialkylalanes: Influence of Transition-metal Complexes
Caporusso, Anna Maria,Giacomelly, Giampaolo,Lardicci, Luciano
, p. 1900 - 1908 (2007/10/02)
The reaction between trialkylalanes and 3-alkyl-, or 4-alkyl-, or 3,4-dialkyl-but-3-en-1-ynes (1) lead to products which correspond to metallation, reduction, and carbalumination processes.The extent of such reactions, and the regio- and stereo-selectivity of the carbalumination, are dependent on the enyne used.A mechanism is proposed involving tautomeric equilibria among several α-unsaturated organoaluminium intermediates to explain the formation of the carbalumination products. In the presence of catalytic amounts of nickel and manganese complexes, 3-en-1-ynes (1), by reacting with tri-isobutylaluminium, are dimerized selectively in a 'head-to-tail' fashion to conjugated tetraenes having different structures in relation to the different nature of the transition-metal complex.The preparative aspect of these induced reactions is discussed, and, in the light of previous reports, some mechanistic considerations are presented.
(Alkenyl-η3-allyl)bis(η5-cyclopentadienyl)titanium Complexes
Lehmkuhl, Herbert,Fustero, Santos
, p. 1353 - 1360 (2007/10/02)
Bis(η5-cyclopentadienyl)titanium hydride (Cp2TiH), presumably formed in situ from bis(η5-cyclopentadienyl)titanium dichloride (1) and isopropylmagnesium bromide (2) adds to the conjugated C=C bonds of the alkatrienes 4, 5, 25, 36, and 45 to give the (alkenyl-η3-allyl)bis(η5-cyclopentadienyl)titanium complexes 7 and 10, 8, 26, and 30, 37, 46.The complexes 7, 8, and 26 with the alkenyl group in position 1 isomerize to give the compounds 27, 28, and 29 in which the C=C bond is conjugated with the allyl group.Compound 37 which contains an alkenyl group in a meso-position does not isomerize.In the case of isomycoren (40), TiH addition occurs primarily to the isolated C=C bond followed by intramolecular cyclization to give the bis(η5-cyclopentadienyl)(1-cyclopentyl-η3-allyl)titanium complex 41.
