Nitrogen Molecule Adsorption on Cationic Tantalum Clusters and Rhodium Clusters and Desorption from Their Nitride Clusters Studied by Thermal Desorption Spectrometry.
Adsorption and desorption of N2 molecules onto cationic Ta and Rh clusters in the gas phase were investigated in the temperature range of 300-1000 K by using thermal desorption spectrometry in combination with density functional theory (DFT) calculations. For Ta6(+), the first N2 molecule was found to adsorb dissociatively, and it remained adsorbed when Ta6(+)N2 was heated to 1000 K. In contrast, the second and the subsequent N2 molecules adsorbed weakly as a molecular form and were released into the gas phase when heated to 600 K. The difference can be explained in terms of the activation barrier between the molecular and dissociative forms. On the other hand, when Ta clusters were generated in the presence of N2 gas by the laser ablation of a Ta rod, isomeric clusters, TanNm(+), having heat resistivity were formed. For Rh6(+), N2 adsorbed molecularly at 300 K and desorbed totally at 450 K. These results were consistent with the DFT calculations, indicating that the dissociative adsorption of N2 is endothermic.
Anionic polymerization mechanism of acrylonitrile trimer anions: key branching point between cyclization and chain propagation.
A cluster anion of vinyl compounds in the gaseous phase has served as one of the simplest microscopic models of the initial stages of anionic polymerization. Herein, we describe our investigations into the initial stage mechanisms of anionic polymerization of acrylonitrile (AN; CH2═CHCN) trimer anions. While the cyclic oligomer is found in mass and photoelectron spectroscopic studies of (AN)3(-), only the chain oligomer is found in the infrared photodissociation (IRPD) spectrum of Ar-tagged (AN)3(-). On the basis of the calculated polymerization pathway of (AN)3(-), we consider that the chain oligomers are the reaction intermediates in the cyclization of (AN)3(-). The rotational isomerization of the (AN)3(-) chain oligomer is found to be the bottleneck in the cyclization of (AN)3(-). To form the (AN)4(-) chain oligomer by chain propagation, the addition of an AN molecule to (AN)3(-) should occur prior to the rotational isomerization. We conclude that the rotational isomerization in the (AN)3(-) chain oligomer is the key branching point between cyclization (termination) or chain propagation in the anionic polymerization.
Highly enantio- and diastereoselective synthesis of β-methyl-γ-monofluoromethyl-substituted alcohols.
Enanatiopure β-methyl-γ-monofluoromethyl alcohols were prepared from the allylic alkylation between fluorobis(phenylsulfonyl)methane with Morita-Baylis-Hillman carbonates. The reaction was catalyzed by using the Cinchona alkaloid derivative, (DHQD)(2)AQN. The origin of the stereoselectivity was verified by DFT methods. Calculated geometries and relative energies of various transition states strongly support the observed stereoselectivity.