Solid supported palladium nano/microparticles were found to be active catalysts to perform mono- and β,β-double-Heck reactions. Different β-unsubstituted and substituted alkenes including acrylate, methacrylate, crotonate, styrene, acrylonitrile, and acrylamide were investigated successfully for mono- and β,β-double-Heck reactions with aryl iodide under milder reaction condition. One-pot β,β-double-Heck reaction of aryl iodides with α,β-unsaturated ester, amide, nitrile, and styrene derivatives were also performed under standard reaction conditions. Wide functional group tolerance, easy catalyst recovery, and recyclability up to twelve times without significant loss of catalytic activity added extra importance to the present process. 相似文献
A new method for the control of string vibration is presented. The method relies on application and removal of a constraint at one point on the string close to one of its boundaries. Application of the constraint temporarily results in two vibrating strings, one of which is significantly shorter in length than the other. The vibration of the shorter length string decays rapidly due to high damping and results in reduction in the overall energy of the system. Removal of the constraint does not change the energy of the system but allows the constraint to be applied repeatedly for vibration suppression. A mathematical model of the cycle of constraint application and removal is presented and multiple cycles of constraint application and removal are simulated. Experiments were performed with a coiled extension spring which behaves like a lightly damped string. Simulation and experimental results match well with each other and demonstrate the efficacy of the simple control strategy. 相似文献
We propose a model for an anisotropic dark energy star where we assume that the radial pressure exerted on the system due
to the presence of dark energy is proportional to the isotropic perfect fluid matter density. We discuss various physical
features of our model and show that the model satisfies all the regularity conditions and is stable as well as singularity-free. 相似文献
PS grafted silica nanoparticles have been prepared by a tandem process that simultaneously employs RAFT polymerization and click chemistry. In a single pot procedure, azide‐modified silica, an alkyne functionalized RAFT agent and styrene are combined to produce the desired product. As deduced by thermal gravimetric and elemental analysis, the grafting density of PS on the silica in the tandem process is intermediate between analogous “grafting to” and “grafting from” techniques for preparing PS brushes on silica. Relative rates of RAFT polymerization and click reaction can be altered to control grafting density.
Toroidal multipoles have recently been explored in various scientific communities, ranging from atomic and molecular physics, electrodynamics, and solid‐state physics to biology. Here we experimentally and numerically demonstrate a three‐dimensionsal toroidal metamaterial where two different toroidal dipoles along orthogonal directions have been observed. The chosen toroidal metamaterial also simultaneously supports Fano resonance and the classical analog of electromagnetically induced transparency (EIT) phenomena in the transmission spectra that originate from the electric–toroidal dipole and electric–magnetic dipole destructive interference. The intriguing properties of the toroidal resonances may open up avenues for applications in toroidal moments generator, sensing and slow‐light devices. 相似文献
We report, herein, a palladium-catalyzed cascade comprising carbopalladation, 1,4-Pd-migration and C(sp2)−C(sp2) bond formation to construct a variety of bis-heterocyclic frameworks in a single operational step. The methodology provides a direct approach to introduce an oxadiazole core at a remote location without any functional group obligation, with moderate to good yields. 相似文献
An expedient one-pot sequential three-component synthesis of a series of diverse spiroindenoquinoxaline pyrrolidine fused nitrochromene derivatives following 1,3-dipolar cycloaddition of azomethine ylides generated in situ by the condensation of indenoquinoxalone and α-amino acids (L-proline and L-phenyl alanine) with 3-nitrochromenes as dipolarophile under classical as well as microwave irradiation is described. The protocol provides a mild reaction condition, high yield of the products, high regioselectivity, and operational simplicity to assemble complex structural entity in a single operation with good to excellent yield. The regio and stereochemical outcome of the cycloaddition reaction is ascertained by spectroscopic and single crystal X-ray analysis. 相似文献
A variety of 2-naphthols have been selectively oxidized to their corresponding 1,1′-bi-2-naphthols in excellent yields with molecular oxygen using methyltrioxorhenium as catalyst. 相似文献