4050-45-7Relevant academic research and scientific papers
UTILIZATION OF SUPERCRITICAL FLUID SOLVENT-EFFECTS IN HETEROGENEOUS CATALYSIS.
Tiltscher,Wolf,Schelschshorn
, p. 897 - 900 (1984)
Comparative studies on fixed-bed catalytic isomerization of 1-hexene and disproportionation of 1,4-diisopropylbenzene were performed under liquid, gaseous or supercritical conditions. The kinetic measurements show that by variation of pressure in the different fluid states catalytic surface reactions as well as mass transfer effects between catalyst and fluid phase and/or transport processes inside porous catalysts can be influenced in a very sensitive way. Conclusions are drawn in view of new possibilities for the direction of yield and selectivity of multiple reactions, for the prolongation of catalyst lifetime, and the study of deactivation mechanisms on heterogeneous catalysts.
Formation and Subsequent Reactivity of a N2-Stabilized Cobalt-Hydride Complex
Krogman, Jeremy P.,Foxman, Bruce M.,Thomas, Christine M.
, p. 3159 - 3166 (2015)
The reduced heterobimetallic Co/Zr complex N2Co(iPr2PNMes)3Zr(THF) (1) has been previously reported to react with the C=O bonds of CO2 and benzophenone to generate Zr/Co μ-oxo complexes OC-Co(iPr2PNMes)2(-O)Zr(iPr2PNMes) (1-CO2) and Ph2C=Co(iPr2PNMes)2(-O)Zr(iPr2PNMes) (1-Ph2CO), respectively. Herein, we report a similar reaction of 1 with pyridine-N-oxide to form an analogous complex (pyridine)Co(iPr2PNMes)2(-O)Zr(iPr2PNMes) (2) with a more labile ligand bound to cobalt. Much like 1-CO2 and 1-Ph2CO, compound 2 reacts with Ph3SiH via formation of a Si-O linkage to form (N2)(H)Co(iPr2PNMes)3ZrOSiPh3 (5). The dinitrogen ligand in 5 is weakly bound and can be readily removed in vacuo or displaced by other L-type ligands. This allows complex 5 to undergo insertion reactions with unsaturated substrates, including diphenyldiazomethane, CO2, benzonitrile, and phenylacetylene to give hydrazonato (Ph2C=NNH)Co(iPr2PNMes)3ZrOSiPh3 (7), formate (OC(H)O)Co(iPr2PNMes)3ZrOSiPh3 (8), ketimide (PhHC=N)Co(iPr2PNMes)3ZrOSiPh3 (9), and ylide Co(PhHC=CHPiPr2NMes)(iPr2PNMes)2ZrOSiPh3 (10) products, respectively. Compound 5 was also found to catalyze the isomerization of 1-hexene to internal isomers.
METAL COMPLEXES IN THE CATALYTIC TRANSFORMATIONS OF OLEFINS. 5. CATALYTIC SYNTHESIS OF C9-C24 OLEFINS FROM PROPYLENE
Furman, D. B.,Ivanov, A. O.,Belyankin, A. Yu.,Pogorelov, A. G.,Yanchevskaya, T. V.,Bragin, O. V.
, p. 1011 - 1014 (1992)
The optimum conditions for the production of C9-C24 olefins with yields of 20-25percent (remainder hexenes) by oligomerization of liquid propylene at the Ni(PPh3)n (n = 2-4)-Et3Al2Cl3 catalytic system were determined by simplex design of experiments.It was shown that the obtained hexenes undergo secondary di- and trimerization reactions.Key words: oligomers, propylene, triphenylphosphinenickel, triethylaluminum.
Microporous Heteropoly Compound as a Shape Selective Catalyst: Cs2.2H0.8PW12O40
Okuhara, Toshio,Nishimura, Toru,Misono, Makoto
, p. 155 - 156 (1995)
The pore size of acidic Cs salts (CsxH3-xPW12O40) was precisely controlled by the Cs content.Cs2.2H0.8PW12O40 possesses micropores in the range from 6.2 to 7.5 Angstroem (in diameter) and exhibits efficient shape selective catalysis toward decomposition of ester, dehydration of alcohol, and alkylation of aromatics in liquid-solid system.This is the first example of shape-selective solid superacid.
A balancing act: Manipulating reactivity of shape-controlled metal nanocatalysts through bimetallic architecture
Laskar,Skrabalak
, p. 6911 - 6918 (2016)
Manipulating the electronic structure of metal nanocrystals is one way of altering their catalytic activities. This ability is demonstrated here by introducing a Au interior to shape-controlled Pd nanocrystals, producing core@shell Au@Pd nanoparticles with varying shell thicknesses. As revealed by X-ray photoelectron spectroscopy, the electronic structure of the Pd shell depends on its thickness. These core@shell nanocrystals were used to catalyze two model reactions: selective hydrogenation of 2-hexyne and oxidation of formic acid, where different reactivities were found also as a function of shell thickness. The comparison of particles with varying bimetallic architecture but identical geometric features provides insight into how electronic regulation in a catalytic reaction can be achieved. It is concluded that a balance in binding interaction between the molecular substrate and catalyst surface is necessary to design an efficient catalyst and can be achieved with shape-controlled core@shell nanocrystals.
The catalytic effect of boron substitution in MCM-41-type molecular sieves
Sundaramurthy,Eswaramoorthi,Lingappan
, p. 631 - 640 (2004)
A series of B-MCM-41 samples has been synthesized with a wide range of boron content (SiO2:B2O3 ratio from 20 to 200), using ethyl silicate ester-40 (ES-40) as the silica source and characterized by XRD, BET, FT-IR, 11B-MAS NMR, SEM, pyridine adsorption, TPDA, and chemical analysis. The interplanar d100 spacing varies from 40 to 45 A, depending on the Si:B ratio. On calcination, a significant amount of four-coordinated boron is converted into less stable three-coordinated boron, and some boron is removed from the framework. The degree of deboronation increases with an increase of boron content of the sample. The B substitution in the MCM-41 framework results in only weak and mild acid sites. The isomerization of 1-hexene is found to be influenced by the boron content in the framework. The isomerization leads to both a hydrogen shift and skeletal rearrangement. The selectivity ratios of cis-2-hexene to trans-2-hexene and 2-hexene to 3-hexene were found to decrease with an increase of temperature and a decrease of the SiO2:B2O3 ratio of the catalysts. Skeletal isomerization starts at 250°C, forming secondary products, and increases with an increase of temperature and an increase of boron content of the catalysts.
A high (Z)/(E) ratio obtained during the 3-hexyne hydrogenation with a catalyst based on a Rh(I) complex anchored on a carbonaceous support
Liprandi, Domingo A.,Cagnola, Edgardo A.,Paredes, Jose F.,Badano, Juan M.,Quiroga, Monica E.
, p. 231 - 237 (2012)
The (Z)/(E) ratio was analyzed for the 3-hexyne semi-hydrogenation at 275, 290 and 303 K. [RhCl(NH2(CH2)12CH 3)3] pure and supported on a carbonaceous material were used as catalysts. The supported complex showed high values of conversion and selectivity, and its behaviour was much better than the Lindlar catalyst used as a reference. Graphical abstract: Conversion to (Z)-3-hexene versus 3-hexyne total conversion as a function of temperature for: (1) Lindlar catalyst, (2) homogeneous complex and (3) anchored complex on RX3.[Figure not available: see fulltext.]
Exohedral functionalization: Vs. core expansion of siliconoids with Group 9 metals: Catalytic activity in alkene isomerization
Giarrana, Luisa,Huch, Volker,Poitiers, Nadine E.,Scheschkewitz, David,Zimmer, Michael
, p. 7782 - 7788 (2020)
Taking advantage of pendant tetrylene side-arms, stable unsaturated Si6 silicon clusters (siliconoids) with the benzpolarene motif (the energetic counterpart of benzene in silicon chemistry) are successfully employed as ligands towards Group 9 metals. The pronounced σ-donating properties of the tetrylene moieties allow for sequential oxidative addition and reductive elimination events without complete dissociation of the ligand at any stage. In this manner, either covalently linked or core-expanded metallasiliconoids are obtained. [Rh(CO)2Cl]2 inserts into an endohedral Si-Si bond of the silylene-functionalized hexasilabenzpolarene leading to an unprecedented coordination sphere of the Rh centre with five silicon atoms in the initial product, which is subsequentially converted to a simpler derivative under reconstruction of the Si6 benzpolarene motif. In the case of [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene) a similar Si-Si insertion leads to the contraction of the Si6 cluster core with concomitant transfer of a chlorine atom to a silicon vertex generating an exohedral chlorosilyl group. Metallasiliconoids are employed in the isomerization of terminal alkenes to 2-alkenes as a catalytic benchmark reaction, which proceeds with competitive selectivities and reaction rates in the case of iridium complexes.
Metallacarboranes in Catalysis. 8. I: Catalytic Hydrogenolysis of Alkenyl Acetates. II: Catalytic Alkene Isomerization and Hydrogenation Revisited
Belmont, James A.,Soto, Jorge,King, Roswell E.,Donaldson, Andrew J.,Hewes, John D.,Hawthorne, M. Frederick
, p. 7475 - 7486 (1989)
Part I of this study describes the facile hydrogenolysis (and deuteriolysis) of alkenyl acetates, such as isopropenyl acetate (D) and 1-phenylvinyl acetate (E), with rhodacarborane catalyst precursors to yield acetic acid and the corresponding alkene.The catalyst precursors employed were (I), (II), and (III).The hydrogenolysis of alkenyl acetates D and E produced propene and styrene, respectively, along with acetic acid in essentially quantitativeyields.Deuterium at Rh was demonstrated not to enter the hydrogenolysis reaction.Use of D2 as the reducing agent with I and E resulted in the incorporation of deuterium into reactant E and products.Styrene produced in these reactions was predominantly d1 with appreciable quantities of d0 and d2.Ethylbenzene, a byproduct resulting from the hydrogenation of styrene, contained only traces of d0 species and was largely d1, d2, and d3.The acetic acid formed in these reactions was isotopically pure CH3COOD.The rate law for E hydrogenolysis with I contained no term showing hydrogen dependence.These results suggest a reaction mechanism for hydrogenolysis that is based upon the relatively slow formation and decomposition of a very reactive rhodium(III) monohydride formed through the regioselective oxidative addition of Rh(I) (in the exo-nido tautomer of the rhodacarborane) to terminal B-H bonds.The monohydride produced in this fashion then enters a cyclic heterolysis process with H2 which leads to rapid product formation.This mechanism suggests that slow B-D/C-H exchange should occur between I-d9 (B-D at all vertices of I) and anisotopically normal alkane, such as 1-hexene (B), during alkene isomerization.Such exchange was observed and shown to be regioselective.This new information predicated part II of this study, which is devoted to a modification of previously advanced proposals for the mechanisms of alkene isomerization and hydrogenation with rhodacarborane precursors.The facile and regioselective exchange of B-H in (IV) with D2 was examined and shown to be electrophilic in character and to apparently proceed through very reactive monohydride intermediates.These new data coupled with previously reported results allow the formulation of unified mechanisms for B-H/D2 and B-H/C-D exchange, alkenyl acetate hydrogenolysis, alkene isomerization, and alkene hydrogenation based upon the key B-Rh(III)-H species formed by the regioselective oxidative addition of terminal B-H bonds to Rh(I) centers.Thus, the effective catalytic sites in all of these reactions appear to be an array of B-Rh(III)-H centers formed reversibly from the Rh(I) present in exo-nido-rhodacarborane tautomers which are, in turn, in equilibrium ...
Komplexkatalyse XXIX. Kationische Allylbis(ligand)nickel(II)hexafluorophosphate PF6 und die Kombination /Et2AlCl als Katalysatoren fuer die Propendimerisation
Balbolov, Entscho,Mitkova, Magdalena,Kurtev, Kurty,Gehrke, Joerg-Peter,Taube, Rudolf
, p. 247 - 256 (1988)
The cationic allylbis(ligand)nickel(II) complexes PF6 with L=P(OPh)3, P(OThym)3 and SbPh3 were found to be efficient catalysts for the oligomerization of propene under a l0 bar pressure of the monomer.The main products are dimers, and specifically the methylpentenes.The /Et2AlCl system catalyzes propene dimerization at atmospheric pressure with high activity, and selectivity similar to that of the cationic allylbis(ligand)nickel(II) complexes.In a kinetic analysis the rate law and the activation parameters ΔH and ΔS were determined for the propene dimerization with this catalytic system.
