18178-60-4Relevant academic research and scientific papers
HYDROGENATION CATALYST
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Page/Page column 61-62, (2022/02/05)
Zinc complexes are described which find use in methods of selective hydrogenation of compounds which contain reducible double or triple bonds, such as the reduction of alkynes to alkenes. The zinc complexes have a general structure according to formula (I): (I) Methods of manufacturing such zinc complexes are also described.
Decamethyltitanocene hydride intermediates in the hydrogenation of the corresponding titanocene-(η2-ethene) or (η2-alkyne) complexes and the effects of bulkier auxiliary ligands
Pinkas, Ji?í,Gyepes, Róbert,Císa?ová, Ivana,Kubi?ta, Ji?í,Horá?ek, Michal,Mach, Karel
, p. 8229 - 8244 (2017/07/10)
1H NMR studies of reactions of titanocene [Cp?2Ti] (Cp? = η5-C5Me5) and its derivatives [Cp?(η5:η1-C5Me4CH2)TiMe] and [Cp?2Ti(η2-CH2CH2)] with excess dihydrogen at room temperature and pressures lower than 1 bar revealed the formation of dihydride [Cp?2TiH2] (1) and the concurrent liberation of either methane or ethane, depending on the organometallic reactant. The subsequent slow decay of 1 yielding [Cp?2TiH] (2) was mediated by titanocene formed in situ and controlled by hydrogen pressure. The crystalline products obtained by evaporating a hexane solution of fresh [Cp?2Ti] in the presence of hydrogen contained crystals having either two independent molecules of 1 in the asymmetric part of the unit cell or cocrystals consisting of 1 and [Cp?2Ti] in a 2:1 ratio. Hydrogenation of alkyne complexes [Cp?2Ti(η2-R1CCR2)] (R1 = R2 = Me or Et) performed at room temperature afforded alkanes R1CH2CH2R2, and after removing hydrogen, 2 was formed in quantitative yields. For alkyne complexes containing bulkier substituent(s) R1 = Me or Ph, R2 = SiMe3, and R1 = R2 = Ph or SiMe3, successful hydrogenation required the application of increased temperatures (70-80 °C) and prolonged reaction times, in particular for bis(trimethylsilyl)acetylene. Under these conditions, no transient 1 was detected during the formation of 2. The bulkier auxiliary ligands η5-C5Me4tBu and η5-C5Me4SiMe3 did not hinder the addition of dihydrogen to the corresponding titanocenes [(η5-C5Me4tBu)2Ti] and [(η5-C5Me4SiMe3)2Ti] yielding [(η5-C5Me4tBu)2TiH2] (3) and [(η5-C5Me4SiMe3)2TiH2] (4), respectively. In contrast to 1, the dihydride 4 did not decay with the formation of titanocene monohydride, but dissociated to titanocene upon dihydrogen removal. The monohydrides [(η5-C5Me4tBu)2TiH] (5) and [(η5-C5Me4SiMe3)2TiH] (6) were obtained by insertion of dihydrogen into the intramolecular titanium-methylene σ-bond in compounds [(η5-C5Me4tBu)(η5:η1-C5Me4CMe2CH2)Ti] and [(η5-C5Me4SiMe3)(η5:η1-C5Me4SiMe2CH2)Ti], respectively. The steric influence of the auxiliary ligands became clear from the nature of the products obtained by reacting 5 and 6 with butadiene. They appeared to be the exclusively σ-bonded η1-but-2-enyl titanocenes (7) and (8), instead of the common π-bonded derivatives formed for the sterically less congested titanocenes, including [Cp?2Ti(η3-(1-methylallyl))] (9). The molecular structure optimized by DFT for compound 1 acquired a distinctly lower total energy than the analogously optimized complex with a coordinated dihydrogen [Cp?2Ti(η2-H2)]. The stabilization energies of binding the hydride ligands to the bent titanocenes were estimated from counterpoise computations; they showed a decrease in the order 1 (-132.70 kJ mol-1), 3 (-121.11 kJ mol-1), and 4 (-112.35 kJ mol-1), in accordance with the more facile dihydrogen dissociation.
Z-selective semihydrogenation of alkynes catalyzed by a cationic vanadium bisimido complex
La Pierre, Henry S.,Arnold, John,Toste, F. Dean
supporting information; experimental part, p. 3900 - 3903 (2011/06/24)
Early metal gets the H: Under 1 atm of H2, the vanadium complex 1 (PFTB=perfluoro-tert-butoxide) catalytically semihydrogenates alkynes to Z alkenes. Synthetic and DFT studies, in combination with H2/D 2 and NMR experiments, indicate that H2 is activated by 1,2-addition to 1. Upon insertion of an alkyne into the V-H bond of A, the product alkene and 1 are generated by the 1,2-α-NH-elimination of the alkenyl ligand.
Highly selective iron-catalyzed synthesis of alkenes by the reduction of alkynes
Enthaler, Stephan,Haberberger, Michael,Irran, Elisabeth
experimental part, p. 1613 - 1623 (2012/06/04)
Herein, the iron-catalyzed reduction of a variety of alkynes with silanes as a reductant has been examined. With a straightforward catalyst system composed of diiron nonacarbonyl and tributyl phosphane, excellent yields and chemoselectivities (>99 %) were obtained for the formation of the corresponding alkenes. After studying the reaction conditions, and the scope and limitations of the reaction, several attempts were undertaken to shed light on the reaction mechanism. Im Rahmen dieser Arbeit wird die Eisen-katalysierte Reduktion von Alkinen zu den entsprechenden Alkenen mit Hilfe von Silanen vorgestellt. Hierbei konnten exzellente Ausbeuten und Selektivitaeten (>99 %) durch die Modifikation des eingesetzten Eisenkatalysators mit Phosphanen beobachtet werden. Nach genauer Untersuchung verschiedenster Reaktionsparameter wurden die hervorragenden Eigenschaften des Katalysatorsystems in der Reduktion zahlreicher Alkine gezeigt. Zum besseren Verstaendnis der Reaktion wurden verschiedene mechanistische Experimente durchgefuehrt. Iron Made′m: In situ generated iron complexes catalyze the reduction of alkynes with silanes as a hydride source with excellent selectivity (>99 %). Copyright
Cross-coupling reaction of thermally stable titanium(II)-alkyne complexes with aryl halides catalysed by a nickel complex
Obora, Yasushi,Moriya, Hiroyuki,Tokunaga, Makoto,Tsuji, Yasushi
, p. 2820 - 2821 (2007/10/03)
The first cross-coupling reaction of thermally stable titanium(II)-alkyne complexes with aryl iodides in the presence of a catalytic amount of Ni(cod)2 is presented.
Functionalised cis-Alkenes from the Stereoselective Decomposition of Diazo Compounds, Catalysed by [RuCl(η5-C5H5)(PPh3)2]
Zotto, Alessandro Del,Baratta, Walter,Verardo, Giancarlo,Rigo, Pierluigi
, p. 2795 - 2802 (2007/10/03)
A catalytic amount of [RuCl(η5-C5H5)(PPh3)2] (1) (0.1 mol- percent) at 60 deg C stereoselectively decomposes α-diazo carbonyl compounds N2CHCOR [R=EtO, Me, Et, nPr, iPr, Ph, (CH2)10Me, and (CH2)14Me] affording quantitatively RCOCH=CHCOR carbene dimers [R=EtO (10), Me (11), Et (12), nPr (13), iPr (14), Ph (15), (CH2)10Me (16), and (CH2)14Me (17)]. The cis isomer is formed in 95-99 percent purity, depending on the R group. Under the same experimental conditions, N2CHCOR1 and N2CHCOR2 react in equimolar amounts to give mixtures of unsymmetrical cis-R1COCH=CHCOR2 (18-32), and symmetrical cis-R1COCH=CHCOR1 and cis-R2COCH=CHCOR2 alkenes. The unsymmetrical cis-alkenes 23-32 are formed in about 50 percent yield from the reaction between two α-diazo ketones. The yield of the cis-R1COCH=CHCOR2 compounds 18-22 increases to ca. 60 percent when a mixture of α-diazo ketone and N2CHCOOEt is catalytically decomposed. Higher conversions into the unsymmetrical products have been obtained by treating N2CHCOR and N2CHSiMe3, from which cis-RCOCH=CHSiMe3 derivatives 34-41 are formed in 83-91 percent yield. The catalytic decomposition of α,ω-bis(diazo) ketones N2CHCO(CH2)nCOCHN2 (n=4, 8, or 10) has also been investigated, and found to afford cyclic cis-alkenes arising from both intra- [n=4 (45), 8 (46), and 10 (47)] and intermolecular carbene-carbene coupling processes.
