1017-22-7Relevant academic research and scientific papers
Catalytic conversion of alcohols over alumina-zirconia mixed oxides: Reactivity and selectivity
Dabbagh, Hossein A.,Zamani, Mehdi
, p. 141 - 148 (2011)
The amorphous and crystalline mixed 25, 50 and 75 wt.% Al2O 3-ZrO2 composites were prepared by means of sol-gel method using aluminum iso-propoxide and zirconyl nitrate precursors. Physicochemical properties were determined using XRD, BET, NH3-TPD, TGA, SEM, and FT-IR spectroscopy. Catalytic activity and selectivity were investigated for the dehydration of 2-octanol and 1,2-diphenyl-2-propanol (DPP). Al 75Zr25 composite is more selective than other forms for the conversion of 2-octanol. The selectivity of DPP for 1-alkene formation was increased over Al25Zr75 catalyst. The crystalline 50 wt.% catalyst dehydrated tertiary alcohol (DPP) selectively in the presence of 2-octanol. The amorphous 50 wt.% catalyst dehydrated DPP predominately to 1-alkene isomer. The crystalline catalyst favored the formation of E-2-alkene.
Synthesis of Polyethylene with In-Chain α,β-Unsaturated Ketone and Isolated Ketone Units: Pd-Catalyzed Ring-Opening Copolymerization of Cyclopropenone with Ethylene
Wang, Xiaoming,Seidel, Falk William,Nozaki, Kyoko
, p. 12955 - 12959 (2019)
Although various functionalized units can be incorporated into polyolefins by transition metal catalyzed coordination copolymerizations of nonfunctionalized olefins with polar functional monomers, the incorporated functional units are largely limited to a C1 unit from either CO or C2 units from vinyl monomers. Reported here is the Pd-catalyzed copolymerization of ethylene with cyclopropenone, leading to incorporation of C3 units with functional groups, α,β-unsaturated ketones, in the chain. Coordination-insertion of the carbonyl group and ring opening of the strained three-membered ring are proposed as the key steps in the mechanism. Under different reaction conditions an isolated ketone structure was afforded as the major carbonyl unit, and could be generated by the copolymerization of ethylene with CO formed in situ from cyclopropenone.
Novel alkylidenating agents via the α lithiation of monoalkyl group 4 metal derivatives: Methylidene-metal complexes and their active lithiated precursors
Eisch, John J.,Adeosun, Adetenu A.
, p. 993 - 997 (2005)
The interaction of the Group 4 metal chlorides, MCl4, where M = Ti, Zr, Hf, with two equiv. of methyllithium at -78 °C in toluene has led to the corresponding methylidene-metal complex, H2C=MCl2, possibly complexed with LiCl. That this complex was stable to at least -40 °C was demonstrated by adding chemical trapping agents at this temperature: 1) benzophenone was quantitatively converted into 1,1-diphenylethylene when M = Ti or Zr; with the Hf analogue, a 1:3 mixture of 1,1-diphenylethylene and 1,1-diphenylethanol was produced; 2) propiophenone reacted with the methylidene complex to yield 2-phenyl-1-butene, 38% (M = Ti) or 25% (M = Zr), with the majority of the propiophenone being recovered (the unreacted ketone is attributed to enolate salt formation competing with the methylidenation); 3) diphenylacetylene reacted with H2C=TiCl2 by cycloaddition in 50% yield, ultimately to give a 1:1 mixture of α-methyl-cis-stilbene and α-methyl-trans-stilbene; and finally 4) norbomene was polymerized in a ROMP process by either the methylidenetitanium or methylidene-zirconium complex, but the titanium catalyst exhibited higher activity. The stability of such methylidene complexes proved to be highly temperature- and solvent-dependent: 1) the methylidene complex in toluene was no longer detectable by chemical trapping when the reaction mixture was warmed to 0 °C or above; 2) the generation of the methylidene complex in THF was uniformly unsuccessful even at -78 °C or above. From these observations this study concludes that in toluene the free methylidene complex, H2C=MCl 2, is not present but rather the agent is still bonded to LiCl. At higher temperatures in toluene or even at -78 °C in THF, the LiCl dissociates from such complexation and the free methylidene dimerizes to [Cl2M-CH2]2, as is known in the case of Cp 2Ti=CH2. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.
Heck reactions catalyzed by Pd(0)-PVP nanoparticles under conventional and microwave heating
Martins, Daniela De L.,Alvarez, Heiddy M.,Aguiar, Lúcia C.S.,Antunes, Octavio A.C.
, p. 47 - 53 (2011)
Pd(0) nanoparticles stabilized by polyvinylpyrrolidone (Pd-PVP) with a diameter of 3-6 nm in ethanol catalyzed Heck coupling of iodobenzene with different alkenes under microwave heating. Products were obtained in good yields (62-99%) and good selectivity to the E-isomers. Microwave heating proved to be superior to conventional heating, providing products in higher yields and selectivities in short times (12 min).
PhCH=P(MeNCH2CH2)3N: A novel ylide for quantitative E selectivity in the wittig reaction
Wang,Zhang,Guzei,Verkade
, p. 3521 - 3524 (2001)
PhCH=P(MeNCH2CH2)3N (1), a semi-stabilized ylide prepared from the commercially available nonionic base P(MeNCH2CH2)3N, reacts with aldehydes to give alkenes in high yield with quantitative E selectivity. In contrast with other ylides, this E selectivity is maintained despite changes in the metal ion of the ionic base used to deprotonate 1, temperature, and solvent polarity. In conjunction with structural parameters gained from the X-ray molecular structure of 1, the pathway to E selectivity in these reactions is rationalized by the Vedejs model of Wittig reaction stereochemistry.
Hydroxypropyl-a-cyclodextrin-capped palladium nanoparticles: active scaffolds for efficient carbon-carbon bond forming cross-couplings in water
Senra, Jaqueline D.,Malta, Luiz Fernando B.,Da Costa, Marcelo E. H. M.,Michel, Ricardo C.,Aguiar, Lucia C. S.,Simas, Alessandro B. C.,Antunes
, p. 2411 - 2422 (2009)
A new approach for the preparation of palladium nanoparticles in water from a renewable source, 2-hydroxypropyl-a-cyclodextrin (a-HPCD), which acts both as a reductant and capping agent, is presented. The palladium nanoparticles were characterized by using dynamic light scattering (DLS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), which revealed the formation of spherical particles in the size range of 2-7 nm. Further analysis by Fourier-transform infrared spectroscopy (FT-IR) and 1H NMR did not show covalent bonds between cyclodextrins and palladium nanoparticles, suggesting that a-HPCD is only physically adsorbed on the nanoparticle surface, presumably through hydrophobic interactions which limit the mutual coalescence of nanoclusters. The catalytic activity was tested in Suzuki, Heck and Sonogashira reactions in neat water, providing good yields and selectivities of coupling products under very low Pd loadings (0.5-0.01 mol%). Remarkably, the nanocatalyst showed significant stability hence the aqueous phase remained active for four subsequent runs. The combination of a binding site for substrates (the HPCD cavity) and a reactive centre (Pd core) provides a potential to explore functional catalysis in aqueous medium.
New transition-state models and kinetics of elimination reactions of tertiary alcohols over aluminum oxide
Dabbagh,Salehi, J. Mohammad
, p. 7619 - 7627 (1998)
A new transition-state model was developed in order to justify the anti intramolecular E2 elimination with cis (Z)-preference over pure alumina and interinolecular E2 elimination with trans (E)-preference over doped alumina. The reactions of model compounds 1,2,3-triphenyl-2-propanol (1), 1,2-diphenyl-2-propanol (2), and 3,3,3-trideuterio-1,2-diphenyl-2-propanol (3) with aluminum oxides with a pH range of 4.5-9.5 and thorium oxide in the temperature range of 200-350 °C in 2-hexanol have been investigated. Over acidic alumina (pH = 4.5 ±0.5), the ratio of E-isomer to Z-isomer (E/Z ? 2) for 2 was found to remain unchanged in this temperature range. At 300 °C, however, Saytzeff elimination favored Hofmann. Over pure alumina the E/Z ratio was equal to 0.650 (2-alkene/1-alkene = 0.750). At equilibrium, the E/Z ratio for 2 was equal to 4.5 with the formation of trace amounts of Hofmann adducts. The ratio of Saytzeff to Hofmann elimination was found to be pH independent. Any decrease in pH caused a slight increase in the E/Z ratio. The average primary kinetic isotope effect (kH/kD) for elimination at 230 °C was equal to 3.775 ± 0.227. The ratio of E/Z over thorium oxide at 300 and 350 °C was similar to that of aluminum oxide at 300 °C, but the Saytzeff elimination was surprisingly favored over Hofmann! The energy of activation (Ea), entropy of activation (AS?), selectivity, isotope effect (kH/kD), and semiempirical calculation (AM1) all agreed with concerted E2 elimination.
Energetics of Twisting in the Lowest Stilbene Triplet State
Saltiel, Jack,Rousseau, Alan D.,Thomas, Babu
, p. 7631 - 7637 (1983)
The temperature dependence of the azulene effect on the benzophenone-sensitized photoisomerization of the stilbenes is reported in toluene, benzene, tert-butyl alcohol, and acetonitrile.The data are consistent with formation of identical stilbene triplets from the two stilbene isomers.Predictions concerning the shape of the potential energy curve for twisting about the central bond depend on the detailed mechanism assumed for the quenching interaction.A lower enthalpy for the twisted triplets is predicted, ΔHtp = -2.1 and -1.6 kcal /mol in toluene and tert-butyl alcohol, respectively, if it is assumed that the equilibrium population of transoid triplet geometries, 3t*, is negligible and that quenching follows encounters of twisted stilbene triplets, 3p*, with azulene when they achieve 3t* geometries in the encounter cage.On the other hand, if quenching is assumed to occur only by direct interaction between 3t* and azulene, equilibrium constants for the 3t* ->/3p* process are obtained which predict a lower enthalpy content for transoid triplets: ΔHtp = 0.5 and 2.9 kcal/mol for toluene and tert-butyl alcohol, respectively.In the latter case entropy is predicted to favor twisted geometries so that for both mechanisms the free energy favors 3p* at the temperatures normally employed for photochemical studies.Reasons for favoring the 3p* quenching mechanism are presented.
Highly-phosphorescent tungsten(0) carbonyl pyridyl-imidazole complexes as photosensitisers
Lee, Jia Jin,Yap, Chew Pheng,Chwee, Tsz Sian,Fan, Wai Yip
, p. 11008 - 11012 (2017)
Photoluminescence data are reported for two W(CO)4L complexes (L = 2-(1H-imidazol-2-yl)pyridine and 2-(2′-pyridyl)benzimidazole) in room-temperature solutions. The bidentate ligands consist of a pyridine and an imidazole moiety connected by a C-C bond. The complexes have been found to exhibit enhanced phosphorescence from the metal-to-ligand charge transfer (MLCT) excited state with quantum yields in the order of 10-3, almost two orders of magnitude higher than those reported for W(CO)4(diimine) complexes. One of the complexes W(CO)4(2-(2′-pyridyl)benzimidazole) can serve as an efficient visible-light photosensitiser for the isomerisation of aromatic alkenes with efficiency comparable to and even exceeding that of the well-studied ruthenium tris-bipyridine complex, Ru(bpy)Cl2.
New deconjugation reaction of (E)-1-indanylidene methylarene brought by photolysis with protic acid
Ho, Tong-Ing,Li, Tai-Chen
, p. 5665 - 5667 (2004)
A new photodeconjugation reaction of (E) indanylidene methylarenes (1a-d) carried out by photolysis in the presence of protic acid are reported with 80% to >95% yields. The reaction mechanism is through the protonation of the less stable (Z) isomer to form stable indanyl cation followed by deprotonation.
