37949-61-4Relevant articles and documents
Highly efficient and recyclable Au nanoparticle-supported palladium(II) interphase catalysts and microwave-assisted alkyne cyclotrimerization reactions in ionic liquids
Lin, Yu-Yun,Tsai, Shih-Chung,Yu, Shuchun Joyce
, p. 4920 - 4928 (2008/12/21)
(Graph Presented) The gold nanoparticles with core diameter of 3.9-4.7 nm were stabilized with octanethiolate and dipyridylphosphinicamido undecanethiolate. Without varying the size of central Au cores, palladium complexes were immobilized onto these Au nanoparticles through chelation to the surface-bound dipyridyls. Hybrid catalysts of this type were dissolvable and precipitable, and their structures and reactions were investigated by solution nuclear magnetic resonance (NMR) spectroscopy with a resolution typically attained for soluble systems. These surface-bound Pd(II) complexes were highly effective catalysts for [2+2+2] alkyne cyclotrimerization reactions to give highly congested benzene rings with fairly good selectivity. The catalytic reactivity of these interphase catalysts was even higher than that of their unbound counterparts. In addition, they can be easily separated and quantitatively recovered by simple filtration. The recovered catalysts can be effectively recycled many times and their electron microscopy images and NMR spectra showed negligible difference from those of freshly prepared. The complete transformation by Au-bound Pd(II) catalyst with a loading of 4 mol % can be achieved within 1 h for most alkynes. The same catalysis can be further accelerated in ionic liquid under microwave conditions to give nearly 100% of cyclotrimerized products in minutes.
Synthesis, characterization, and alkyne cyclotrimerization chemistry of titanium complexes supported by calixarene-derived bis(aryloxide) ligation
Ladipo, Folami T.,Sarveswaran, Vallipuram,Kingston, Jesudoss V.,Huyck, Rebecca A.,Bylikin,Carr, Shana D.,Watts, Randy,Parkin, Sean
, p. 502 - 514 (2007/10/03)
Proximally bridged calix[4]arene compounds (DESC)H2 (3), (DMSHC)H2 (4), (DMSMC)H2 (5), and (DPSC)H2 (6), in which one R2Si group (R=alkyl or aryl) bridges adjacent oxygens, were synthesized via reaction between dialkyl- or diaryldichlorosilane and the corresponding calix[4]arene. Treatment of p- tert -butylcalix[4]arene with Ph2SiCl2 at room temperature or (o-MeC6 H4)2SiCl2 at 80 °C gave (ClPh2SiCl)2Calix-H2 (7) and (o-Tol2SiCl)2Calix-H2 (8), respectively. Titanium dichloride complexes 9-12 (L2 TiCl2, where L2=DESC, DMSHC, DMSMC, or DPSC) were prepared in high yield from reaction of 3-6 with TiCl4. The molecular structures of 7 and 12 were established by single-crystal X-ray diffraction studies. Reduction of 9, 11, and 12 with activated magnesium (Mg*) in the presence of an excess of Me3SiC≡CH produced titananorbornadiene complexes L2Ti{η6-1,2,4-C6H3 (SiMe3)3} (13-15, L2=DESC, DMSMC, or DPSC), which were characterized in solution. Catalytic cyclotrimerization of both terminal and internal alkynes was achieved using catalyst systems derived from L2TiCl2 complexes 9-12 and Mg*. For unsymmetrically substituted internal alkynes, preference for 1,2,4-substitution decreased as the size difference of the substituent groups decreased. The cyclotrimerization of PhC≡CMe was more facile when the calixarene-derived bis(aryloxide) ligand was DPSC versus DMSMC, suggesting that the DPSC ligand may provide a less crowded titanium center and exert greater kinetic control over the course of the cyclotrimerization.
Charge-transfer probes for molecular recognition via steric hindrance in donor-acceptor pairs
Rathore,Lindeman,Kochi
, p. 9393 - 9404 (2007/10/03)
Molecular association of various aromatic hydrocarbons (D, including sterically hindered donors) with a representative group of diverse acceptors (A = quinone, trinitrobenzene, tetracyanoethylene, tropylium, tetranitromethane, and nitrosonium) is visually apparent in solution by the spontaneous appearance of distinctive colors. Spectral (UV-vis) analyses of the colored solutions reveal their charge-transfer origin (λ(CT)) and they provide quantitative information of the intermolecular association in the form of the K(DA) and ε(CT) values for the formation and visualization, respectively, of different [D,A] complexes. Importantly, such measurements establish charge-transfer absorption to be a sensitive analytical tool for evaluating the steric inhibition of donor-acceptor association. For example, the steric differences among various hindered aromatic donors in their association with quinone are readily dramatized in their distinctive charge-transfer (color) absorptions and verified by X-ray crystallography of the charge-transfer crystals and/or QUANTA molecular modeling calculations of optimum intermolecular separations allowed by van der Waals contacts.
