122425-32-5Relevant academic research and scientific papers
Catalysis of Diels-Alder Reactions by Low Oxidation State Transition-Metal Lewis Acids: Fact and Fiction
Bonnesen, Peter V.,Puckett, Craig L.,Honeychuck, Robert V.,Hersh. William H.
, p. 6070 - 6081 (1989)
Catalysis of Diels-Alder reactions between the dienes cyclopentadiene, butadiene, isoprene, and piperylene and the enones acrolein, methyl vinyl ketone, and methyl acrylate is induced by 0.1-2.5 mol percent of mer-(cis-Me3P)(trans-NO)(CO)3W(μ-F)SbF5 (1), (Cy2PCH2CH2PPh2)(CO)2(NO)W(μ-F)SbF5 (2), Cp(CO)2FeL(1+)X(1-) (L = THF, X(1-) = BF4(1-), 3a; X(1-) = SbF6(1-), 3b; L = ν1-acrolein, X(1-) = PF6(1-), 3d), or Cp(CO)2L'ML(1+)PF6(1-) (L' = CO, L = acrolein, M = Mo, 4a; L' = PPh3, L = THF, M = Mo, 4b; L' = CO, L = THF, M = W, 4c).Enhancement of rates and regio- and stereoselectivity is observed compared to the thermal reactions; the order of apparent catalytic activity is 1 > 2 ca. 3a > 4a, 4c.The order of Lewis acidity is 1 > 2 > 4a > 3a, casting doubt on the role of Cp(CO)2Fe(1+) in catalysis.The potential impurity Ag(1+)BF4(1-) is similarly reactive, although not in lower concentrations.Use of 2,6-di-tert-butylpyridine (5) and 1-(n-butyl)-2,2,6,6-tetramethylpiperidine (6) as hindered bases to trap Ag(1+) and H(1+) in the presence of transition-metal Lewis acids is described.Substoichiometric use of 5 demonstrates that Ag(1+)BF4(1-) is not the real catalyst and that the true activity of 3a is low.Use of 5 with stronger acids, namely the acrolein adduct of 1 (1a) and 4a, or of the stronger base 6 with 3a leads to catalyst destruction, via a pathway proposed to involve deprotonation of coordinated methylene chloride.The reactivity of other potential impurities (HBF4*Et2O, BF3*Et2O, Ph3C(1+)PF6(1-), and NO(1+)SbF6(1-)) is briefly examined, as is that of analogues of 3a that have different counterions.Kinetic analysis of stoichiometric reactions of metal-acrolein adducts with isoprene shows that the relative rates of cycloaddition for 1a, the acrolein adduct of 2, 4a, and 3d are 68:20:8:1 and that the rate-determinig step in the catalytic reactions is the rate of aldehyde turnover.The calculated rate constants are used to predict catalytic yields and demostrate that 1 and 2 can be the real catalysts.For 3a and possibly 4a as well, the observed catalytic activity is significantly greater than expected on the basis of the stoichiometrically determined rate constants, so the real catalysis in these cases apparently is due to the presence of much more reactive materials present as impurities.
Palladium catalysed alkyne hydrogenation and oligomerisation: A parahydrogen based NMR investigation
Lopez-Serrano, Joaquin,Duckett, Simon B.,Dunne, John P.,Godard, Cyril,Whitwood, Adrian C.
supporting information; body text, p. 4270 - 4281 (2009/02/03)
The role phosphine ligands play in the palladium(ii)-bis-phosphine-hydride cation catalysed hydrogenation of diphenylacetylene is explored through a PHIP (parahydrogen induced polarization) NMR study. The precursors Pd(LL′)(OTf)2 (1a-e) [LL′ = dcpe (PCy2CH 2CH2PCy2), dppe, dppm, dppp, cppe (PCy 2CH2CH2PPh2)] are used. Alkyl palladium intermediates of the type [Pd(LL′)(CHPhCH2Ph)](OTf) (2 and 3) are detected and demonstrated to play an active role in hydrogenation catalysis. Magnetization transfer experiments reveal chemical exchange from the α-H of the alkyl ligand of 2a (LL′ = dcpe) and linkage isomer 2e′ (LL′ = cppe) into trans-stilbene on the NMR timescale. Activation parameters (ΔH≠ and ΔS≠) for this transformation have been determined. These experiments, coupled with GC/MS data, indicate that the catalytic activity is greater in methanol, where it follows the order: dcpe > cppe > dppp > dppe > dppm, than in CD 2Cl2. All five of the phosphine systems described are less active than those based on bcope [where bcope is (C8H 14)PCH2-CH2P(C8H14)] and tbucope [where tbucope is (C8H 14)PC6H4CH2P(tBu) 2]. cis, cis-1,2,3,4-Tetraphenyl-buta-1,3-diene is detected as a minor reaction product with Pd(LL′)(PhCH-CHPh-CPh=CHPh)+ (4) also being shown to play a role in the alkyne dimerisation step.
A new route to achiral and chiral 1,2-bis(phosphino)ethanes, 1-arsino-2-phosphinoethanes, and 1,3-bis(phosphino)propanes and the molecular structure and catalytic activity of some rhodium(I) complexes derived thereof
Fries, Guido,Wolf, Justin,Ilg, Kerstin,Walfort, Bernhard,Stalke, Dietmar,Werner, Helmut
, p. 1873 - 1881 (2007/10/03)
A series of unsymmetrical 1,2-bis(phosphino)ethanes R2PCH 2CH2PR′2 (2a-d) and 1-arsino-2- phosphinoethanes R2AsCH2CH2PR′ 2 (3a-c) mainly with bulky substituants R and
A new synthetic route to unsymmetrical 1,2-bis(phosphanyl)ethanes and 1,2-arsanyl(phosphanyl)ethanes with and without a stereogenic center
Fries, Guido,Wolf, Justin,Pfeiffer, Matthias,Stalke, Dietmar,Werner, Helmut
, p. 564 - 566 (2007/10/03)
A one-pot reaction affords unsymmetrical 1,2-bis(phosphanyl)ethanes 2 and 1,2-arsanyl(phosphanyl)ethanes 3 from the cyclic sulfate 1 in high yield. Similarly, chiral 1,2-bis(phosphanyl)ethanes and 1,3-bis(phosphanyl)propanes could be obtained in enantiomerically pure form. R, R'= alkyl, phenyl.
