822-50-4Relevant articles and documents
INTRAMOLECULAR CYCLIZATIONS OF ORGANOMETALLIC COMPOUNDS IV. HETEROATOM INFLUENCE ON CYCLIZATIONS OF ORGANOLITHIUM COMPOUNDS
Smith, Michael J.,Wilson, Stanley E.
, p. 4615 - 4618 (1981)
Alkoxyl groups in alkenyllithiums can influence the stereochemistry of cyclization.The presence of n-butyllithium increases the stereoselectivity such that only one stereochemistry results; the presence of TMEDA negates the heteroatom's influence so that only the other stereochemistry results.Yields are 33percent to 44percent.
Insights into the Major Reaction Pathways of Vapor-Phase Hydrodeoxygenation of m-Cresol on a Pt/HBeta Catalyst
Sun, Qianqian,Chen, Guanyi,Wang, Hua,Liu, Xiao,Han, Jinyu,Ge, Qingfeng,Zhu, Xinli
, p. 551 - 561 (2016/02/20)
Conversion of m-cresol was studied on a Pt/HBeta catalyst at 225-350°C and ambient hydrogen pressure. At 250°C, the reaction proceeds through two major reaction pathways: (1) direct deoxygenation to toluene (DDO path); (2) hydrogenation of m-cresol to methylcyclohexanone and methylcyclohexanol on Pt, followed by fast dehydration on Br?nsted acid sites (BAS) to methylcyclohexene, which is either hydrogenated to methylcyclohexane on Pt or ring-contracted to dimethylcyclopentanes and ethylcyclopentane on BAS (HYD path). The initial hydrogenation is the rate-determining step of the HYD path as its rate is significantly lower than those of subsequent steps. The apparent activation energy of the DDO path is 49.7 kJ mol-1 but the activation energy is negative for the HYD path. Therefore, higher temperatures lead to the DDO path becoming the dominant path to toluene, whereas the HYD path, followed by fast equilibration to toluene, is less dominant, owing to the inhibition of the initial hydrogenation of m-cresol.
Synthesis, reactivity, and catalytic application of a nickel pincer hydride complex
Breitenfeld, Jan,Scopelliti, Rosario,Hu, Xile
experimental part, p. 2128 - 2136 (2012/06/01)
The nickel(II) hydride complex [(MeN2N)Ni-H] (2) was synthesized by the reaction of [(MeN2N)Ni-OMe] (6) with Ph2SiH2 and was characterized by NMR and IR spectroscopy as well as X-ray crystallography. 2 was unstable in solution, and it decomposed via two reaction pathways. The first pathway was intramolecular N-H reductive elimination to give MeN2NH and nickel particles. The second pathway was intermolecular, with H2, nickel particles, and a five-coordinate Ni(II) complex [(MeN2N)2Ni] (8) as the products. 2 reacted with acetone and ethylene, forming [( MeN2N)Ni-OiPr] (9) and [(MeN 2N)Ni-Et] (10), respectively. 2 also reacted with alkyl halides, yielding nickel halide complexes and alkanes. The reduction of alkyl halides was rendered catalytically, using [(MeN2N)Ni-Cl] (1) as catalyst, NaOiPr or NaOMe as base, and Ph2SiH2 or Me(EtO)2SiH as the hydride source. The catalysis appears to operate via a radical mechanism.
Study of Ir/WO3/ZrO2-SiO2 ring-opening catalysts: Part II. Reaction network, kinetic studies and structure-activity correlation
Lecarpentier, Sebastien,van Gestel, Jacob,Thomas, Karine,Gilson, Jean-Pierre,Houalla, Marwan
, p. 49 - 63 (2008/09/17)
The present paper is the second part of a systematic study of the influence of W and Ir loading on the activity of Ir/WO3/ZrO2-SiO2 catalysts for the ring-opening reaction of naphthenic molecules using methylcyclohexane (MCH) as a model compound. A series of Si-stabilized tungstated zirconias, WOx/ZrO2-SiO2, containing up to 3.5 atom W/nm2, was prepared. Ir-based catalysts containing up to 1.2 wt% were obtained by impregnation of these solids. Characterization of the metal dispersion and catalyst acidity was described in a previous article. The objective of the present study was to determine the best metal/acid balance for optimal performance of Ir/WOx/ZrO2-SiO2 catalysts in the ring-opening reaction of MCH. Monofunctional (acid WOx/ZrO2-SiO2 or metal Ir/ZrO2-SiO2) and bifunctional (Ir/WO3/ZrO2-SiO2) catalysts were examined. Based on the analysis of the yields and products distributions, a reaction network was proposed, and kinetic data (e.g., activation energies, initial rates) were calculated. Correlations between characterization results obtained earlier (e.g., acidity, dispersion) and catalytic performance are also reported. The monofunctional acid catalysts WOx/ZrO2-SiO2 showed a low selectivity for ring opening. The ring-contraction activity developed for W surface density above a threshold value of 1 atom W/nm2. This was attributed to the appearance and the development of a relatively strong Broensted acidity monitored by infrared measurements. MCH ring contraction and C5 naphthene ring opening occur according to a classic acid mechanism. For low conversions, the monofunctional metal catalysts Ir/ZrO2-SiO2 exhibited significant selectivity for ring opening that decreased with increasing conversion. Because of the lack of ring-contraction products, the observed activity was attributed to the direct ring opening of the MCH. Ring opening and cracking occur according to a dicarbene mechanism. The study of MCH conversion on Ir/WOx/ZrO2-SiO2 catalysts indicated that MCH ring contraction to alkylcyclopentanes occurs before ring opening. The best yields for ring opening were obtained with the 1.2% Ir/WOx/ZrO2 (1.5 atom of W/nm2). Further increases in W surface density led to a decrease in the indirect ring-opening yield, attributed to a decrease in Ir dispersion. For bifunctional metal/acid catalysts, analysis of the mechanism is less straightforward. The activation energy for C6 ring contraction and indirect C6 ring opening is a function of the metal/acid ratio. For high ratios, indirect ring opening occurs essentially over metallic sites. A decrease in the metal/acid ratio enhances the contribution of acid mechanism.
