279-23-2Relevant articles and documents
Norbornane: An investigation into its valence electronic structure using electron momentum spectroscopy, and density functional and Green's function theories
Knippenberg,Nixon,Brunger,Maddern,Campbell,Trout,Wang,Newell,Deleuze,Francois,Winkler
, p. 10525 - 10541 (2004)
We report on the results of an exhaustive study of the valence electronic structure of norbornane (C7H12), up to binding energies of 29 eV. Experimental electron momentum spectroscopy and theoretical Green's function and density functional theory approaches were all utilized in this investigation. A stringent comparison between the electron momentum spectroscopy and theoretical orbital momentum distributions found that, among all the tested models, the combination of the Becke-Perdew functional and a polarized valence basis set of triple-ζ quality provides the best representation of the electron momentum distributions for all of the 20 valence orbitals of norbornane. This experimentally validated quantum chemistry model was then used to extract some chemically important properties of norbornane. When these calculated properties are compared to corresponding results from other independent measurements, generally good agreement is found. Green's function calculations with the aid of the third-order algebraic diagrammatic construction scheme indicate that the orbital picture of ionization breaks down at binding energies larger than 22.5 eV. Despite this complication, they enable insights within 0.2 eV accuracy into the available ultraviolet photoemission and newly presented (e,2e) ionization spectra, except for the band associated with the 1a2-1 one-hole state, which is probably subject to rather significant vibronic coupling effects, and a band at ～25 eV characterized by a momentum distribution of "s-type" symmetry, which Green's function calculations fail to reproduce. We note the vicinity of the vertical double ionization threshold at ～26 eV.
Boryl-metal bonds facilitate cobalt/nickel-catalyzed olefin hydrogenation
Lin, Tzu-Pin,Peters, Jonas C.
, p. 13672 - 13683 (2014)
New approaches toward the generation of late first-row metal catalysts that efficiently facilitate two-electron reductive transformations (e.g., hydrogenation) more typical of noble-metal catalysts is an important goal. Herein we describe the synthesis of a structurally unusual S = 1 bimetallic Co complex, [(CyPBP)CoH]2(1), supported by bis(phosphino)boryl and bis(phosphino)hydridoborane ligands. This complex reacts reversibly with a second equivalent of H2(1 atm) and serves as an olefin hydrogenation catalyst under mild conditions (room temperature, 1 atm H2). A bimetallic Co species is invoked in the rate-determining step of the catalysis according to kinetic studies. A structurally related NiINiIdimer, [(PhPBP)Ni]2(3), has also been prepared. Like Co catalyst 1, Ni complex 3 displays reversible reactivity toward H2, affording the bimetallic complex [(PhPBHP)NiH]2(4). This reversible behavior is unprecedented for NiIspecies and is attributed to the presence of a boryl-Ni bond. Lastly, a series of monomeric (tBuPBP)NiX complexes (X = Cl (5), OTf (6), H (7), OC(H)O (8)) have been prepared. The complex (tBuPBP)NiH (7) shows enhanced catalytic olefin hydrogenation activity when directly compared with its isoelectronic/isostructural analogues where the boryl unit is substituted by a phenyl or amine donor, a phenomenon that we posit is related to the strong trans influence exerted by the boryl ligand.
Synthesis, characterization, and evaluation of iron nanoparticles as hydrogenation catalysts in alcohols and tetraalkylphosphonium ionic liquids: Do solvents matter?
Banerjee, Abhinandan,Yao, Yali,Durr, Michael-Roy R.,Barrett, William G.,Hu, Yongfeng,Scott, Robert W. J.
, p. 5207 - 5216 (2018)
Iron nanoparticles (Fe NPs) synthesized via a one-pot chemical reduction strategy in neat alcohol or water/alcohol mixtures are compared to and contrasted with those synthesized in tetraalkylphosphonium ionic liquids with respect to their catalytic activities for the hydrogenation of simple olefins. It was observed that Fe NPs could catalyze the conversion of 2-norbornene to norbornane and 1-octene to octane in good yields under moderately high hydrogen pressures. Core-shell type Fe@FexOy particles in alcoholic solvents with larger sizes show greater resistance to catalytic deactivation after several reaction cycles, whereas halide ionic liquid-capped Fe particles show a marked tendency towards oxidative degradation, which limits their utility in catalysis unless rigorous anhydrous and anoxic conditions are maintained. Finally, in situ X-ray absorption spectroscopy was applied to determine the fate of these systems upon catalysis and exposure to air. No change in Fe speciation was seen for Fe@FexOy nanoparticles in alcohol solvents. Fe nanoparticles in ionic liquids with strongly coordinating anions such as halides were not particularly stable to oxidation, while those in ionic liquids with non-coordinating anions agglomerate during catalysis, as well as undergoing slow oxidative degradation, thus making these systems less useful for catalysis compared to their counterparts in alcoholic solvents.
Hydrogenation via photochemically generated diimide
Squillacote,De Felippis,Lai
, p. 4137 - 4140 (1993)
Diimide is a well-known reagent for hydrogenating multiple bonds with very high stereospecificity. However, all of the methods for generating diimide require somewhat rigorous conditions. We show here that 1-thia-3,4-diazolidine-2,5-dione (TDADH) can be used to photochemically produce diimide at room temperature under neutral conditions. The diimide thus produced can hydrogenate multiple bonds in high yields.
Modulation of σ-Alkane Interactions in [Rh(L2)(alkane)]+ Solid-State Molecular Organometallic (SMOM) Systems by Variation of the Chelating Phosphine and Alkane: Access to η2,η2-σ-Alkane Rh(I), η1-σ-Alkane Rh(III) Complexes, and Alkane Encapsulation
Martínez-Martínez, Antonio J.,Tegner, Bengt E.,McKay, Alasdair I.,Bukvic, Alexander J.,Rees, Nicholas H.,Tizzard, Graham J.,Coles, Simon J.,Warren, Mark R.,Macgregor, Stuart A.,Weller, Andrew S.
, p. 14958 - 14970 (2018)
Solid/gas single-crystal to single-crystal (SC-SC) hydrogenation of appropriate diene precursors forms the corresponding σ-alkane complexes [Rh(Cy2P(CH2)nPCy2)(L)][BArF4] (n = 3, 4) and [RhH(Cy2P(CH2)2(CH)(CH2)2PCy2)(L)][BArF4] (n = 5, L = norbornane, NBA; cyclooctane, COA). Their structures, as determined by single-crystal X-ray diffraction, have cations exhibiting Rh···H-C σ-interactions which are modulated by both the chelating ligand and the identity of the alkane, while all sit in an octahedral anion microenvironment. These range from chelating η2,η2 Rh···H-C (e.g., [Rh(Cy2P(CH2)nPCy2)(η2η2-NBA)][BArF4], n = 3 and 4), through to more weakly bound η1 Rh···H-C in which C-H activation of the chelate backbone has also occurred (e.g., [RhH(Cy2P(CH2)2(CH)(CH2)2PCy2)(η1-COA)][BArF4]) and ultimately to systems where the alkane is not ligated with the metal center, but sits encapsulated in the supporting anion microenvironment, [Rh(Cy2P(CH2)3PCy2)][CO?BArF4], in which the metal center instead forms two intramolecular agostic η1 Rh···H-C interactions with the phosphine cyclohexyl groups. CH2Cl2 adducts formed by displacement of the η1-alkanes in solution (n = 5; L = NBA, COA), [RhH(Cy2P(CH2)2(CH)(CH2)2PCy2)(κ1-ClCH2Cl)][BArF4], are characterized crystallographically. Analyses via periodic DFT, QTAIM, NBO, and NCI calculations, alongside variable temperature solid-state NMR spectroscopy, provide snapshots marking the onset of Rh···alkane interactions along a C-H activation trajectory. These are negligible in [Rh(Cy2P(CH2)3PCy2)][CO?BArF4]; in [RhH(Cy2P(CH2)2(CH)(CH2)2PCy2)(η1-COA)][BArF4], σC-H → Rh σ-donation is supported by Rh → σ?C-H pregostic donation, and in [Rh(Cy2P(CH2)nPCy2)(η2η2-NBA)][BArF4] (n = 2-4), σ-donation dominates, supported by classical Rh(dπ) → σ?C-H π-back-donation. Dispersive interactions with the [BArF4]- anions and Cy substituents further stabilize the alkanes within the binding pocket.
Metal-catalyzed addition polymers for 157 nm resist applications. Synthesis and polymerization of partially fluorinated, ester-functionalized tricyclo [4.2.1.02,5]non-7-enes
Sanders, Daniel P.,Connor, Eric F.,Grubbs, Robert H.,Hung, Raymond J.,Osborn, Brian P.,Chiba, Takashi,MacDonald, Scott A.,Grant Willson,Conley, Will
, p. 1534 - 1542 (2003)
Fluorinated tricyclo[4.2.1.02,5]non-7-ene-3-carboxylic acid esters are shown to undergo metal-catalyzed addition polymerization. The resulting homopolymers are transparent at 157 nm and demonstrate the utility of these monomers in development of photoresists for 157 nm lithography. Fluorinated tricyclononene (TCN) structures with ester substituents exhibit up to 3 orders of magnitude more transparency at 157 nm than conventional ester-functionalized norbornene structures as determined by gas-phase vacuum-ultraviolet spectroscopy and variable angle spectroscopic ellipsometry. Unlike their fluorinated norbornene counterparts, the fluorinated, ester-functionalized TCN monomers successfully undergo transition-metal-catalyzed addition polymerization to produce polymers with high glass transition temperatures and the etch resistance required for photolithographic resist materials applications. The potential use of fluorinated TCN structures for 157 nm photoresists is demonstrated through the synthesis and characterization of TCN monomers and polymers.
Comparison of alkene hydrogenation in carbon nanoreactors of different diameters: Probing the effects of nanoscale confinement on ruthenium nanoparticle catalysis
Aygün, Mehtap,Stoppiello, Craig T.,Lebedeva, Maria A.,Smith, Emily F.,Gimenez-Lopez, Maria Del Carmen,Khlobystov, Andrei N.,Chamberlain, Thomas W.
, p. 21467 - 21477 (2017)
The catalytic properties of ruthenium nanoparticles (RuNPs) supported in carbon nanoreactors of different diameters-single walled carbon nanotubes (SWNTs, width of cavity 1.5 nm) and hollow graphitised nanofibers (GNFs, width of cavity 50-70 nm)-were evaluated using exploratory alkene hydrogenation reactions and compared to RuNPs adsorbed on the surface of SWNT or deposited on carbon black in commercially available Ru/C. Supercritical CO2 is shown to be essential to enable efficient transport of reactants to the catalytic RuNPs, particularly for the very narrow RuNP@SWNT nanoreactors. Though the RuNPs in SWNT are observed to be highly active, they simultaneously reduce the accessible volume of very narrow SWNTs by 30-40% resulting in lower overall turnover numbers (TONs). In contrast, RuNPs confined in wider GNFs were completely accessible and demonstrated remarkable activity compared to unconfined RuNPs on the outer surface of SWNTs or carbon black. Control of the nanoscale environment around the catalytic RuNPs significantly enhances the stability of the catalyst and influences the local concentration of reactant molecules in close proximity to the RuNPs, illustrating the comparable importance of confinement to that of metal loading and size of NPs in the catalyst. Interestingly, extreme spatial confinement also appeared not to be the best strategy for controlling the selectivity of hydrogenations in a competitive reaction of norbornene and benzonorbornadiene, with wider RuNP@GNF nanoreactors displaying enhanced selectivity for the hydrogenation of the aromatic group containing alkene (benzonorbornadiene). This is attributed to the presence of nanoscale graphitic step-edges within the GNF making them an attractive alternative to the extremely narrow SWNT nanoreactors for preparative catalysis.
Fluoroacrylate-bound fluorous-phase soluble hydrogenation catalysts
Bergbreiter, David E.,Franchina, Justine G.,Case, Brenda L.
, p. 393 - 395 (2000)
(GRAPHS PRESENTED) Fluoroacrylate polymer-bound hydrogenation catalysts are described. N-Acryloxysuccinimide-containing fluoroacrylate polymers were converted into phosphine ligands and subsequently into analogues of Wilkinson's catalyst by amidation of N-acryloxysuccinimide active ester residues and Rh exchange. The resulting catalysts have excellent activity and can be reused following fluorous biphasic liquid/liquid separation and extraction.
Unravelling the reaction path of rhodium-monophos-catalysed olefin hydrogenation
Alberico, Elisabetta,Baumann, Wolfgang,De Vries, Johannes G.,Drexler, Hans-Joachim,Gladiali, Serafino,Heller, Detlef,Henderickx, Huub J. W.,Lefort, Laurent
, p. 12683 - 12695 (2011)
The mechanism of the asymmetric hydrogenation of methyl (Z)-2-acetamidocinnamate (mac) catalysed by [Rh(MonoPhos)2(nbd)] SbF6 (MonoPhos: 3,5-dioxa-4-phosphacyclohepta[2,1-a:3,4-a] dinaphthalen-4-yl)dimethylamine) was elucidated by using 1H, 31P and 103Rh NMR spectroscopy and ESI-MS. The use of nbd allows one to obtain in pure form the rhodium complex that contains two units of the ligand. In contrast to the analogous complexes that contain cis,cis-1,5-cyclooctadiene (cod), this complex shows well-resolved NMR spectroscopic signals. Hydrogenation of these catalyst precursors at 1 bar total pressure gave rise to the formation of a bimetallic complex of general formula [Rh(MonoPhos)2]2(SbF6)2; no solvate complexes were detected. In the dimeric complex both rhodium atoms are ligated to two MonoPhos ligands but, in addition, each rhodium atom also binds to one of the binaphthyl rings of a ligand that is bound to the other rhodium metal. Upon addition of mac, a mixture of diastereomeric complexes [Rh(MonoPhos) 2(mac)]SbF6 is formed in which the substrate is bound in a chelate fashion to the metal. Upon hydrogenation, these adducts are converted into a new complex [Rh(MonoPhos)2{mac(H)2}]SbF6 in which the methyl phenylalaninate mac(H)2 is bound through its aromatic ring to rhodium. Addition of mac to this complex leads to displacement of the product by the substrate. No hydride intermediates could be detected and no evidence was found for the involvement at any stage of the process of complexes with only one coordinated MonoPhos. The collected data suggest that the asymmetric hydrogenation follows a Halpern-like mechanism in which the less abundant substrate-catalyst adduct is preferentially hydrogenated to phenylalanine methyl ester. Dimers are forever: Reaction intermediates around the catalytic cycle of the asymmetric hydrogenation of methyl (Z)-2-acetamidocinnamate by [Rh(MonoPhos)2(nbd)]SbF6 (nbd=bicyclo[2.2.1]hepta-2,5-diene) catalyst (see scheme) were detected by using 1H, 31P and 103Rh NMR spectroscopy and ESI-MS. The asymmetric hydrogenation appears to follow a Halpern-like mechanism.
Heterometallic Mg?Ba Hydride Clusters in Hydrogenation Catalysis
Wiesinger, Michael,Knüpfer, Christian,Elsen, Holger,Mai, Jonathan,Langer, Jens,Harder, Sjoerd
, p. 4567 - 4577 (2021/09/09)
Reaction of a MgN“2/BaN”2 mixture (N“=N(SiMe3)2) with PhSiH3 gave three unique heterometallic Mg/Ba hydride clusters: Mg5Ba4H11N”7 ? (benzene)2 (1), Mg4Ba7H13N“9 ? (toluene)2 (2) and Mg7Ba12H26N”12 (3). Product formation is controlled by the Mg/Ba ratio and temperature. Crystal structures are described. While 3 is fully insoluble, clusters 1 and 2 retain their structures in aromatic solvents. DFT calculations and AIM analyses indicate highly ionic bonding with Mg?H and Ba?H bond paths. Also unusual H????H? bond paths are observed. Catalytic hydrogenation with MgN“2, BaN”2 and the mixture MgN“2/BaN”2 has been studied. Whereas MgN“2 is only active in imine hydrogenation, alkene and alkyne hydrogenation needs the presence of Ba. The catalytic activity of the MgN”2/BaN“2 mixture lies in general between that of its individual components and strong cooperative effects are not evident.
