Pd(II)-Catalyzed cyclogeneration of carbocations: subsequent rearrangement and trapping under oxidative conditions

A catalytic oxidative polycyclization reaction initiated by the carbocyclization of 1,5-dienes with Pd(II) is reported. Trapping of a putative carbocation with suitable functional groups (phenols, alkenes, alcohols, sulfonamide), or rearrangement protocols (Pinacol) yields poly-cyclic products in good yields and in excellent diastereoselectivities. Turnover of the intermediate Pd-C bond is via β-H elimination.     

Uncommon ferromagnetic interactions in a homometallic Co(II) chain bridged by a single end-to-end azide

A new one-dimensional heterochiral coordination polymer [Co(bmdt)(N3)2].MeCN (1.MeCN) with well-isolated chains was prepared via a self-assembly process. Magnetic data show that intrachain ferromagnetic couplings via the single end-to-end azide group are observed, which is an extraordinary case among the azide-bridged Co(II) systems.     

Plasmonic Hotspots in Air: An Omnidirectional Three‐Dimensional Platform for Stand‐Off In‐Air SERS Sensing of Airborne Species

Molecular‐level airborne sensing is critical for early prevention of disasters, diseases, and terrorism. Currently, most 2D surface‐enhanced Raman spectroscopy (SERS) substrates used for air sensing have only one functional surface and exhibit poor SERS‐active depth. “Aerosolized plasmonic colloidosomes” (APCs) are introduced as airborne plasmonic hotspots for direct in‐air SERS measurements. APCs function as a macroscale 3D and omnidirectional plasmonic cloud that receives laser irradiation and emits signals in all directions. Importantly, it brings about an effective plasmonic hotspot in a length scale of approximately 2.3 cm, which affords 100‐fold higher tolerance to laser misalignment along the z‐axis compared with 2D SERS substrates. APCs exhibit an extraordinary omnidirectional property and demonstrate consistent SERS performance that is independent of the laser and analyte introductory pathway. Furthermore, the first in‐air SERS detection is demonstrated in stand‐off conditions at a distance of 200 cm, highlighting the applicability of 3D omnidirectional plasmonic clouds for remote airborne sensing in threatening or inaccessible areas.     

Kinetics and mechanism of the pyridinolysis of phenacyl bromides in acetonitrile

Kinetic studies of the reactions of substituted phenacyl bromides (YC6H4COCH2Br) with pyridines (XC5H4N) are carried out in acetonitrile at 45.0 degrees C. A biphasic Bronsted plot is obtained with a change in slope from a large (betaX approximately equals 0.65-0.80) to a small (betaX approximately 0.36-0.40) value at pKa = 3.2-3.6, which can be attributed to a change in the rate-determining step from breakdown to formation of a tetrahedral intermediate in the reaction path as the basicity of the pyridine nucleophile increases. This mechanism is supported by the faster rates with pyridines than with anilines and the change of cross-interaction constant rhoXY from a large positive (rhoXY = +1.4) to a small positive (rhoXY approximately +0.1) value. The large magnitude of Hammett rhoX (= -5.5 to -6.9) values for the pyridines with electron-withdrawing substituents and positive deviations of the pi-acceptors, p-CH3CO and p-CN, are quite similar to those for the pyridinium ion formation equilibria. The activation parameters are also in line with the proposed mechanism.