75-28-5Relevant articles and documents
Rational Preparation of Well-Defined Multinuclear Iridium-Aluminum Polyhydride Clusters and Comparative Reactivity
Camp, Clément,Del Rosal, Iker,Escomel, Léon,Jeanneau, Erwann,Maron, Laurent,Robin, Emmanuel,Soulé, Na?me,Thieuleux, Chloé
, (2022/02/10)
We report an original alkane elimination approach, entailing the protonolysis of triisobutylaluminum by the acidic hydrides from Cp*IrH4. This strategy allows access to a series of well-defined tri- and tetranuclear iridium aluminum polyhydride clusters, depending on the stoichiometry: [Cp*IrH3Al(iBu)2]2(1), [Cp*IrH2Al(iBu)]2(2), [(Cp*IrH3)2Al(iBu)] (3), and [(Cp*IrH3)3Al] (4). Contrary to most transition-metal aluminohydride complexes, which can be considered as [AlHx+3]x-aluminates and LnM+moieties, the situation here is reversed: These complexes have original structures that are best described as [Cp*IrHx]n-iridate units surrounding cationic Al(III) fragments. This is corroborated by reactivity studies, which show that the hydrides are always retained at the iridium sites and that the [Cp*IrH3]-moieties are labile and can be transmetalated to yield potassium ([KIrCp*H3], 8) or silver (([AgIrCp*H3]n, 10) derivatives of potential synthetic interest. DFT calculations show that the bonding situation can vary in these systems, from 3-center 2-electron hydride-bridged Lewis adducts of the form Ir-H←Al to direct polarized metal-metal interaction from donation of d-electrons of Ir to the Al metal, and both types of interactions take place to some extent in each of these clusters.
Hydrogenative metathesis of enynes via piano-stool ruthenium carbene complexes formed by alkyne gem-hydrogenation
Peil, Sebastian,Bistoni, Giovanni,Goddard, Richard,Fürstner, Alois
supporting information, p. 18541 - 18553 (2020/11/17)
The only recently discovered gem-hydrogenation of internal alkynes is a fundamentally new transformation, in which both H atoms of dihydrogen are transferred to the same C atom of a triple bond while the other position transforms into a discrete metal carbene complex. [Cp?RuCl]4 is presently the catalyst of choice: the resulting piano-stool ruthenium carbenes can engage a tethered alkene into either cyclopropanation or metathesis, and a prototypical example of such a reactive intermediate with an olefin ligated to the ruthenium center has been isolated and characterized by X-ray diffraction. It is the substitution pattern of the olefin that determines whether metathesis or cyclopropanation takes place: a systematic survey using alkenes of largely different character in combination with a computational study of the mechanism at the local coupled cluster level of theory allowed the preparative results to be sorted and an intuitive model with predictive power to be proposed. This model links the course of the reaction to the polarization of the double bond as well as to the stability of the secondary carbene complex formed, if metathesis were to take place. The first application of "hydrogenative metathesis"to the total synthesis of sinularones E and F concurred with this interpretation and allowed the proposed structure of these marine natural products to be confirmed. During this synthesis, it was found that gem-hydrogenation also provides opportunities for C-H functionalization. Moreover, silylated alkynes are shown to participate well in hydrogenative metathesis, which opens a new entry into valuable allylsilane building blocks. Crystallographic evidence suggests that the polarized [Ru-Cl] bond of the catalyst interacts with the neighboring R3Si group. Since attractive interligand Cl/R3Si contacts had already previously been invoked to explain the outcome of various ruthenium-catalyzed reactions, including trans-hydrosilylation, the experimental confirmation provided herein has implications beyond the present case.
Decarbonylative ether dissection by iridium pincer complexes
Yoo, Changho,Dodge, Henry M.,Farquhar, Alexandra H.,Gardner, Kristen E.,Miller, Alexander J.M.
, p. 12130 - 12138 (2020/11/26)
A unique chain-rupturing transformation that converts an ether functionality into two hydrocarbyl units and carbon monoxide is reported, mediated by iridium(i) complexes supported by aminophenylphosphinite (NCOP) pincer ligands. The decarbonylation, which involves the cleavage of one C-C bond, one C-O bond, and two C-H bonds, along with formation of two new C-H bonds, was serendipitously discovered upon dehydrochlorination of an iridium(iii) complex containing an aza-18-crown-6 ether macrocycle. Intramolecular cleavage of macrocyclic and acyclic ethers was also found in analogous complexes featuring aza-15-crown-5 ether or bis(2-methoxyethyl)amino groups. Intermolecular decarbonylation of cyclic and linear ethers was observed when diethylaminophenylphosphinite iridium(i) dinitrogen or norbornene complexes were employed. Mechanistic studies reveal the nature of key intermediates along a pathway involving initial iridium(i)-mediated double C-H bond activation. This journal is
Synthesis and catalytic performance of zeolite-Y supported on silicon carbide in n-heptane cracking
Alhassan, Saeed M.,Berthod, Mikael,Dabbawala, Aasif A.,Joseph, Tony,Khan, Shaihroz,Mittal, Hemant,Morin, Stephane,Singaravel, Gnana,Vaithilingam, Balasubramanian V.,Wahedi, Yasser Al
, (2020/10/27)
In this work, we demonstrate a facile approach for the synthesis of zeolite-Y crystals (size, ca. ～400 nm) supported on silicon carbide (SiC) with the assistance of the cationic template (polydiallyldimethylammonium chloride, PDDA). The polymeric cationic template used to treat SiC particles induces a positive charge on SiC surface which electrostatically attracts negatively charged aluminosilicate seeds and promotes the growth of zeolite (ZY) particles over SiC, thus leading to the formation of stable ZY?SiC supported catalysts. The supported ZY catalysts with different weight ratio of ZY and SiC were synthesized and characterized by various techniques such as XRD, SEM, SEM-EDX, SEM-mapping, TEM, STEM, FT-IR, 27Al MAS NMR and N2 sorption. The characterization of the supported ZY catalysts suggests the uniform growth of ZY particles over SiC together with the creation of hierarchical micro-mesopores assembly. In the catalytic cracking of n-heptane, the catalyst ZY?SiC-50 displayed a remarkable improvement in reaction rate when compared to commercial zeolite-Y (CBV-600) amounting to 3.5 folds enhancement. Interestingly, the light olefins yield is also substantially improved. At WHSV of 8 h?1 and 475 °C, the highest light olefin yield (24–36 %) was achieved over ZY?SiC-50 whereas the reference catalyst, CBV-600 produced lower light olefins yield (7–17 %). Moreover, the supported ZY catalyst exhibited less deactivation rates. This improved performance is attributed to the hierarchical micro-mesopores assembly created by the homogeneous dispersion of zeolite crystals on SiC which offers fast diffusion pathways for the reactants and enhanced accessibility to active sites thus leading to higher observed reaction rates and fast diffusion of products thus minimizing the occurrence of side reactions.
PREPARATION METHOD FOR PREPARING A CATALYST BASED ON IRON NANOPARTICLES, COBALT NANOPARTICLES OR ALLOYS THEREOF, THE CATALYST THUS PREPARED AND USE OF THE CATALYST FOR THE SELECTIVE HYDROGENATION OF CARBON DIOXIDE TO ISOBUTANE
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Page/Page column 14-15; 17-18, (2020/06/19)
The present invention describes a preparation method for preparing a catalyst made up of a Fe and Co metal alloy in several ratios in the form of nanoparticles embedded in a graphitic carbon matrix. Another object of the invention is also the prepared catalyst which in a surprising manner selectively catalyses the hydrogenation of carbon dioxide into isobutane.
Impact of the Spatial Organization of Bifunctional Metal–Zeolite Catalysts on the Hydroisomerization of Light Alkanes
Cheng, Kang,Harmel, Justine,Oenema, Jogchum,Sunley, Glenn,Yoshida, Hideto,Ze?evi?, Jovana,Zhang, Zhaorong,de Jong, Krijn P.,van der Wal, Lars I.
supporting information, p. 3592 - 3600 (2020/02/05)
Improving product selectivity by controlling the spatial organization of functional sites at the nanoscale is a critical challenge in bifunctional catalysis. We present a series of composite bifunctional catalysts consisting of one-dimensional zeolites (ZSM-22 and mordenite) and a γ-alumina binder, with platinum particles controllably deposited either on the alumina binder or inside the zeolite crystals. The hydroisomerization of n-heptane demonstrates that the catalysts with platinum particles on the binder, which separates platinum and acid sites at the nanoscale, leads to a higher yield of desired isomers than catalysts with platinum particles inside the zeolite crystals. Platinum particles within the zeolite crystals impose pronounced diffusion limitations on reaction intermediates, which leads to secondary cracking reactions, especially for catalysts with narrow micropores or large zeolite crystals. These findings extend the understanding of the ??intimacy criterion” for the rational design of bifunctional catalysts for the conversion of low-molecular-weight reactants.
Room Temperature Acceptorless Alkane Dehydrogenation from Molecular σ-Alkane Complexes
McKay, Alasdair I.,Bukvic, Alexander J.,Tegner, Bengt E.,Burnage, Arron L.,Mart?nez-Mart?nez, Antonio J.,Rees, Nicholas H.,Macgregor, Stuart A.,Weller, Andrew S.
supporting information, p. 11700 - 11712 (2019/08/20)
The non-oxidative catalytic dehydrogenation of light alkanes via C-H activation is a highly endothermic process that generally requires high temperatures and/or a sacrificial hydrogen acceptor to overcome unfavorable thermodynamics. This is complicated by alkanes being such poor ligands, meaning that binding at metal centers prior to C-H activation is disfavored. We demonstrate that by biasing the pre-equilibrium of alkane binding, by using solid-state molecular organometallic chemistry (SMOM-chem), well-defined isobutane and cyclohexane σ-complexes, [Rh(Cy2PCH2CH2PCy2)(η: η-(H3C)CH(CH3)2][BArF4] and [Rh(Cy2PCH2CH2PCy2)(η: η-C6H12)][BArF4] can be prepared by simple hydrogenation in a solid/gas single-crystal to single-crystal transformation of precursor alkene complexes. Solid-gas H/D exchange with D2 occurs at all C-H bonds in both alkane complexes, pointing to a variety of low energy fluxional processes that occur for the bound alkane ligands in the solid-state. These are probed by variable temperature solid-state nuclear magnetic resonance experiments and periodic density functional theory (DFT) calculations. These alkane σ-complexes undergo spontaneous acceptorless dehydrogenation at 298 K to reform the corresponding isobutene and cyclohexadiene complexes, by simple application of vacuum or Ar-flow to remove H2. These processes can be followed temporally, and modeled using classical chemical, or Johnson-Mehl-Avrami-Kologoromov, kinetics. When per-deuteration is coupled with dehydrogenation of cyclohexane to cyclohexadiene, this allows for two successive KIEs to be determined [kH/kD = 3.6(5) and 10.8(6)], showing that the rate-determining steps involve C-H activation. Periodic DFT calculations predict overall barriers of 20.6 and 24.4 kcal/mol for the two dehydrogenation steps, in good agreement with the values determined experimentally. The calculations also identify significant C-H bond elongation in both rate-limiting transition states and suggest that the large kH/kD for the second dehydrogenation results from a pre-equilibrium involving C-H oxidative cleavage and a subsequent rate-limiting β-H transfer step.
Hydrogen Activation and Hydrogenolysis Facilitated by Late-Transition-Metal-Aluminum Heterobimetallic Complexes
Charles, R. Malcolm,Yokley, Timothy W.,Schley, Nathan D.,Deyonker, Nathan J.,Brewster, Timothy P.
, p. 12635 - 12645 (2019/10/11)
Previously reported heterobimetallic rhodium-aluminum and iridium-aluminum alkyl complexes are shown to activate hydrogen, generating the corresponding alkane. Kinetic data indicate a mechanistic difference between the iridium- A nd rhodium-based systems. In both cases the transition metal is an active participant in the release of alkane from the aluminum center. For iridium-aluminum species, experimental mechanistic data suggest that multiple pathways occur concomitantly with each other: One being the oxidative addition of hydrogen followed by proton transfer resulting in alkane generation. Computational data indicate a reasonable barrier to formation of an iridium dihydride intermediate observed experimentally. In the case of the rhodium-aluminum species, hydrides are not observed spectroscopically, though a reasonable barrier to formation of this thermodynamically unstable species has been calculated. Alternative mechanistic possibilities are discussed and explored computationally. Cooperative hydrogenolysis mechanisms are computed to be energetically unfeasible for both metal centers.
Hydrocarbon Synthesis via Photoenzymatic Decarboxylation of Carboxylic Acids
Zhang, Wuyuan,Ma, Ming,Huijbers, Mieke M. E.,Filonenko, Georgy A.,Pidko, Evgeny A.,Van Schie, Morten,De Boer, Sabrina,Burek, Bastien O.,Bloh, Jonathan Z.,Van Berkel, Willem J. H.,Smith, Wilson A.,Hollmann, Frank
supporting information, p. 3116 - 3120 (2019/03/06)
A recently discovered photodecarboxylase from Chlorella variabilis NC64A (CvFAP) bears the promise for the efficient and selective synthesis of hydrocarbons from carboxylic acids. CvFAP, however, exhibits a clear preference for long-chain fatty acids thereby limiting its broad applicability. In this contribution, we demonstrate that the decoy molecule approach enables conversion of a broad range of carboxylic acids by filling up the vacant substrate access channel of the photodecarboxylase. These results not only demonstrate a practical application of a unique, photoactivated enzyme but also pave the way to selective production of short-chain alkanes from waste carboxylic acids under mild reaction conditions.
Hydrogenation of CO2 into aromatics over a ZnCrO: X-zeolite composite catalyst
Zhang, Junfeng,Zhang, Meng,Chen, Shuyao,Wang, Xiaoxing,Zhou, Zeling,Wu, Yingquan,Zhang, Tao,Yang, Guohui,Han, Yizhuo,Tan, Yisheng
supporting information, p. 973 - 976 (2019/01/23)
A ZnCrOx-ZnZSM-5 composite catalyst was used for CO2 hydrogenation into hydrocarbons especially aromatics (Aro). 81.1% Aro selectivity in C5+ hydrocarbons (mainly C5-11) was obtained at 320 °C, corresponding to 19.9% CO2 conversion, 29.8% total hydrocarbons (HCt) selectivity and 69.7% C5+ selectivity in HCt. Our optimized STY of Aro is the highest ever reported.
