1560-60-7Relevant academic research and scientific papers
A Comparative Analysis of the CO-Reducing Activities of MoFe Proteins Containing Mo- and V-Nitrogenase Cofactors
Lee, Chi Chung,Tanifuji, Kazuki,Newcomb, Megan,Liedtke, Jasper,Hu, Yilin,Ribbe, Markus W.
, p. 649 - 653 (2018/04/16)
The Mo and V nitrogenases are structurally homologous yet catalytically distinct in their abilities to reduce CO to hydrocarbons. Here we report a comparative analysis of the CO-reducing activities of the Mo- and V-nitrogenase cofactors (i.e., the M and V clusters) upon insertion of the respective cofactor into the same, cofactor-deficient MoFe protein scaffold. Our data reveal a combined contribution from the protein environment and cofactor properties to the reactivity of nitrogenase toward CO, thus laying a foundation for further mechanistic investigation of the enzymatic CO reduction, while suggesting the potential of targeting both the protein scaffold and the cofactor species for nitrogenase-based applications in the future.
Reaction Mechanism and Kinetics of Olefin Metathesis by Supported ReOx/Al2O3 Catalysts
Lwin, Soe,Wachs, Israel E.
, p. 272 - 278 (2016/01/12)
The self-metathesis of propylene by heterogeneous supported ReOx/Al2O3 catalysts was investigated with in situ Raman spectroscopy, isotopic switch (D-C3= → H-C3=), temperature-programmed surface reaction (TPSR) spectroscopy, and steady-state kinetic studies. The in situ Raman studies showed that two distinct surface ReO4 sites are present on alumina and that the olefins preferentially interact with surface ReO4 sites anchored at acidic surface sites of alumina (olefin adsorption: C4= > C3= > C2=). The isotopic switch experiments demonstrate that surface Re?CH3 and Re?CHCH3 are present during propylene metathesis, with Re? representing activated surface rhenia sites. At low temperatures (3=][Re?]2. At high temperatures (>100 °C), the rate-determining step is the recombination of two surface propylene molecules (rate ≈ [C3=]2[Re?]). To a lesser extent, the recombination of surface Re?CH3 and Re?CHCH3 intermediates also contributes to self-metathesis of propylene at elevated reaction temperatures.
Active Sites in Olefin Metathesis over Supported Molybdena Catalysts
Amakawa, Kazuhiko,Kr?hnert, Jutta,Wrabetz, Sabine,Frank, Benjamin,Hemmann, Felix,J?ger, Christian,Schl?gl, Robert,Trunschke, Annette
, p. 4059 - 4065 (2015/12/26)
Metathesis of propene to ethene and 2-butenes was studied over a series of MoOx/SBA-15 catalysts (molybdenum oxide supported on mesoporous silica SBA-15; Mo loading 2.1-13.3 wt %, apparent Mo surface density 0.2-2.5 nm-2). The catalysts have been prepared by an ion exchange technique. Nitrogen adsorption, 1H MAS-NMR, Raman, and FTIR spectroscopies were applied to characterize the catalysts. Adsorption of the reactant propene and the probe molecule NH3 was studied by in situ FTIR spectrometry microcalorimetry and temperature-programmed desorption. Irrespective of the loading, only ≈1 % of the Mo atoms in the MoOx/SiO2 catalysts transform into active carbene (Mo=CHR) sites catalyzing propene metathesis. Isolated, distorted molybdenum di-oxo species in close vicinity to two silanol groups have been shown to be the precursor of the active site. Targeted active site creation by pretreatment with methanol resulted in an increase in initial catalytic activity by a factor of 800. Targeted active site creation: Only ≈1 % of isolated distorted Mo di-oxo species that are in close vicinity to two silanol groups have been shown to be the precursor of the active carbene (Mo=CHR) sites on MoOx/SiO2 catalysts for propene metathesis. Targeted active site creation resulted in an increase in initial catalytic activity by a factor of 800.
Reduction of fluorinated cyclopropene by nitrogenase
Ni, Feng,Lee, Chi Chung,Hwang, Candy S.,Hu, Yilin,Ribbe, Markus W.,Mckenna, Charles E.
, p. 10346 - 10352 (2013/08/23)
Reduction of the first known halogen-containing substrate by nitrogenase (N2ase), 3,3-difluorocyclopropene (DFCP), was investigated. Reduction requires both N2ase proteins (MoFe and Fe protein), ATP, and an exogenous reductant (dithionite, DT), as with N2 and known alternative substrates of the enzyme. Two major products providing evidence for reductive C-F bond cleavage were confirmed, propene (P1, requiring 6e -/6H+) and 2-fluoropropene (P2, 4e-/4H +). Both were identified by GC-MS and NMR spectroscopy, and had the same Km constants (0.022 atm, 5.4 mM). Reduction of 1,2-dideuterated DFCP (d2-DFCP) further revealed that (i) in both P1 and P2, two deuterium atoms are retained, one on carbon-1 and one on carbon-3, indicating that C=C bond cleavage rather than C-C bond cleavage is involved during DFCP reduction at least to P2 (assuming no F migration); (ii) no selectivity was observed in formation of cis and trans isomers of 1,3-d2-2- fluoropropene, whereas cis-1,3-d2-propene is the predominant 1,3-d2-propene product, indicating that one of the bound reduction intermediates on the pathway to propene is constrained geometrically. A reduction mechanism, consistent with hydride transfer as a key step, is discussed. Reductive C-F bond cleavage is an ability of N2ase that further demonstrates the unique and remarkable scope of its catalytic prowess.
In situ generation of active sites in olefin metathesis
Amakawa, Kazuhiko,Wrabetz, Sabine,Kroehnert, Jutta,Tzolova-Mueller, Genka,Schloegl, Robert,Trunschke, Annette
supporting information; experimental part, p. 11462 - 11473 (2012/09/05)
The depth of our understanding in catalysis is governed by the information we have about the number of active sites and their molecular structure. The nature of an active center on the surface of a working heterogeneous catalyst is, however, extremely difficult to identify and precise quantification of active species is generally missing. In metathesis of propene over dispersed molybdenum oxide supported on silica, only 1.5% of all Mo atoms in the catalyst are captured to form the active centers. Here we combine infrared spectroscopy in operando with microcalorimetry and reactivity studies using isotopic labeling to monitor catalyst formation. We show that the active Mo(VI)-alkylidene moieties are generated in situ by surface reaction of grafted molybdenum oxide precursor species with the substrate molecule itself gaining insight into the pathways limiting the number of active centers on the surface of a heterogeneous catalyst. The active site formation involves sequential steps requiring multiple catalyst functions: protonation of propene to surface Mo(VI)-isopropoxide species driven by surface Bronsted acid sites, subsequent oxidation of isopropoxide to acetone in the adsorbed state owing to the red-ox capability of molybdenum leaving naked Mo(IV) sites after desorption of acetone, and oxidative addition of another propene molecule yielding finally the active Mo(VI)-alkylidene species. This view is quite different from the one-step mechanism, which has been accepted in the community for three decades, however, fully consistent with the empirically recognized importance of acidity, reducibility, and strict dehydration of the catalyst. The knowledge acquired in the present work has been successfully implemented for catalyst improvement. Simple heat treatment after the initial propene adsorption doubled the catalytic activity by accelerating the oxidation and desorption-capturing steps, demonstrating the merit of knowledge-based strategies in heterogeneous catalysis. Molecular structure of active Mo(VI)-alkylidene sites derived from surface molybdena is discussed in the context of similarity to the highly active Schrock-type homogeneous catalysts.
Tracing the hydrogen source of hydrocarbons formed by vanadium nitrogenase
Lee, Chi Chung,Hu, Yilin,Ribbe, Markus W.
experimental part, p. 5545 - 5547 (2011/07/08)
Hydrocarbons from CO: The vanadium-nitrogenase-catalyzed reduction of carbon monoxide involves the adenosine triphosphate (ATP)-dependent protonation of CO and the subsequent formation of C - C bonds, leading to the production of small hydrocarbons, such as C2H4, C2H 6, C3H6, and C3H8 (see picture). Isotope-substitution studies monitored by GC-MS analysis show that protons are the source of hydrogen for the CO reduction. Copyright
A unique Pd4 platform with CH3 and μ-CH 2 groups and its C-C coupling reaction with simple olefins
Sachse, Anna,John, Michael,Meyer, Franc
supporting information; scheme or table, p. 1986 - 1989 (2010/06/19)
(Chemical Equation Presented) Menage a quatre: The Pd 4 complex 1 features both terminal CH3 and bridging CH2 groups, and it reacts with ethylene at room temperature to give mainly propene. NMR spectroscopic studies reveal several intermediates in the formation of 1 from Pd2 building blocks.
Mechanism of the reaction of vinyl chloride with (α-diimine)PdMe + species
Kilyanek, Stefan M.,Stoebenau, Edward J.,Vinayavekhin, Nawaporn,Jordan, Richard F.
experimental part, p. 1750 - 1760 (2010/06/13)
The reaction of vinyl chloride (VC) with (α-diimine)PdMe+ species yields (α-diimine)PdCl(propene)+. Isotope labeling experiments using the deuterium-labeled vinyl chlorides 1-VC-d1 and Z-VC-d1 combined with DFT
Mild and selective deuteration and isomerization of alkenes by a bifunctional catalyst and deuterium oxide
Erdogan, Guelin,Grotjahn, Douglas B.
supporting information; experimental part, p. 10354 - 10355 (2009/12/08)
(Figure Presented) H/D exchange is achieved at allylic positions of alkenes using D2O in acetone and alkene isomerization catalyst 1, which features a bifunctional imidazolylphosphine. The basic nitrogen of the latter is thought to deprotonate an alkene substrate coordinated to the CpRu center; at this stage the protonated nitrogen could undergo H/D exchange with deuterium oxide. An exceptional degree of deuteration is achieved at positions accessible to isomerization, with a high degree of control. Using biphasic settings one can literally wash out reactive protons on the substrate without using organic solvents.
Coupling reactions in aldehydes adsorbed on V(100) single-crystal surfaces
Shen, Min,Zaera, Francisco
experimental part, p. 8708 - 8713 (2009/10/23)
The thermal chemistry of formaldehyde on vanadium (100) single-crystal surfaces was characterized under ultrahigh vacuum (UHV) conditions by using temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) in combination with isotope-labeling experiments. Particular emphasis was placed on establishing a mechanism for the formation of ethylene, which was observed to desorb in two temperature regimes, at 290 and 540 K. The low-temperature reaction was determined to occur via the coupling of methylene groups formed on the surface upon dissociation of the C-O bond in adsorbed formaldehyde. The high-temperature ethylene, on the other hand, was proven to require the prior formation of a diolate, -OCH2CH2O-, intermediate. This chemistry was shown to be quite general, also occuring in cross-coupling mode between two different coadsorbed aldehydes.
