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Density functional theory (DFT) calculations show that H2 evolution is attributed to active sulfur hydrides derived from MoS2 complexes via two- or three-electron reduction from the synthesized [(PY5Me2)MoS2]2+. Water acts as a bridge for H2 evolution from the intermolecular H+/H- coupling between sulfur hydride complexes and hydrated protons.

A highly enantioselective iridium-catalyzed hydrogenation of α-keto amides to form α-hydroxy amides has been achieved with excellent results (up to >99% conversion and up to >99% ee, TON up to 100 000). As an example, this protocol was applied to the synthesis of (S)-4-(2-amino-1-hydroxyethyl)benzene-1,2-diol, the enantiomer of norepinephrine, which is widely used as an injectable drug for the treatment of critically low blood pressure. Density functional theory (DFT) calculations were also carried out to reveal the reaction mechanism.

As the first cascade C–H activation directed by a transient group, reaction of alkynols and 7-oxabenzonorbornadienes has been achieved via synergistic rhodium and scandium catalysis to afford spirocyclic dihydrobenzo[a]fluorenefurans. This transformation proceeds by a transient hemiketal group directed C–H activation, dehydrative naphthylation, and intramolecular Prins-type cyclization. Mechanistic studies and density functional theory calculations indicate that the rate-determining step is C–H bond cleavage and both the transient hemiketal group and synergistic RhIII/ScIII catalysis play key roles.

Platinum bis(dithiolene) complexes have reactivity toward alkenes like nickel bis(dithiolene) complexes. We examined the uptake of 1,3-butadiene by platinum bis(dithiolene) [Pt(tfd)2] (tfd = S2C2(CF3)2) via a density functional theory study; both 1,2- and 1,4-additions of 1,3-butadiene to the ligands of Pt(tfd)2 to form both interligand and intraligand adducts were studied. For single 1,3-butadiene addition, direct 1,4-addition on interligand S-S, 1,2-addition on intraligand S-S, and 1,4-addition on intraligand S-C are all feasible at room temperature and are controlled by the symmetry of the highest occupied molecular orbital of 1,3-butadiene and the lowest unoccupied molecular orbital of Pt(tfd)2. However, the formation of the interligand S-S adduct through 1,4-addition of one molecule of cis-1,3-butadiene is the most favorable route, with a reaction barrier of 9.3 kcal/mol. The other two addition processes cannot compete with this one due to both higher reaction barriers and unstable adducts. Other possible pathways, such as formation of cis-interligand S-S adduct from 1,2-addition of one molecule of 1,3-butadiene via a twisted trans-interligand S-S adduct, have higher barriers. Our calculated results show that 1,4-addition of a single molecule of 1,3-butadiene on the interligand S-S gives the kinetically stable product by a one-step pathway. But of at least equal importance is the apofacial 1,4-addition of two molecules of 1,3-butadiene on the intraligand S-C of the same ligand on Pt(tfd)2, which yields the thermodynamically stable product, obtained via a short lifetime intermediate, the 1:1 intraligand S-C adduct, being formed through several pathways. The calculated results in this study well explain the experimental observation that 1:1 interligand S-S adduct was formed in a short time, and the intraligand S-C adduct from two molecules of cis-1,3-butadiene was accumulated in 20 h at 50° and characterized by X-ray crystallography.

In this paper, we report the design of numerous models of CsC(n)(-) (n = 1-10). By means of B3LYP density functional method, we carried out geometry optimization and calculation on the vibrational frequency. We found that the CsC(n)(-) (n = 4-10) clusters with Cs lightly embraced by C(n) are ground-state isomers. The structures are composed of C(n)(2-) and Cs(+) with the former being electronically stabilized by the latter. When n is even, the C(n) (n = 4-10) chain is polyacetylene-like. The CsC(n)(-) (n = 1-10) with even n are found to be more stable than those with odd n, and the result is in accord with the relative intensities of CsC(n)(-) (n = 1-10) observed in mass spectrometric studies. In this paper, we provide explanations for such trend of even/odd alternation based on concepts of the highest vibrational frequency, incremental binding energy, electron affinity, and dissociation channels.

The electronic structures of bcc Fe [100](001) edge dislocation core system and the corresponding Nb (V) doped system are investigated by using the first-principles discrete variational method within the framework of density functional theory. The Nb (V) doped dislocation core system is found to be more stable than the clean dislocation core system. Nb (V) can stay steadily at the dislocation core system by way of substitution, and give rise to the strong interactions and the charge transfers with the neighboring Fe atoms. Particularly, the Fe-Fe bonds across the slip plane are enhanced in the Nb (V) doped dislocation core system, which are expected to affect the slipping characteristics of the edge dislocation. (C) 2006 Elsevier B.V. All rights reserved.

The alloying effect of the refractory elements Ta and W on the electronic structure of γ-TiAl is investigated by using the first-principles discrete variational method within the framework of density functional theory. The impurity formation energy result indicates that Ta and W can stay steadily in the TiAl system by way of substitution. The Mulliken population, density of states and charge density difference results show that Ta and W both give rise to the strong interaction between themselves and the neighboring host atoms. The alloying effect of the two elements on γ-TiAl is the same.

Using molecular graphics software, we designed numerous models of CnN3− (n=1–8). Geometry optimization and calculation on vibration frequency were carried out by the B3LYP density functional method. After comparison of structure stability, we found that the structures of ground-state CN3− and C2N3− are bent chains with a nitrogen atom at either end, whereas when n=3–8, the ground-state clusters show three branches, each with a nitrogen atom located at the end. When n=5–8, the longest branch of CnN3− is polyacetylenelike. When n=5 or 7, the longest branch is connected to the central sp2 carbon in a nonlinear manner. The CnN3− (n=1–8) with an even number of carbon atoms are more stable than those with odd numbers, matching the peak pattern observed in laser-induced mass spectra of CnN3−. The trend of such odd/even alternation is explained based on concepts of bonding characteristics, electron affinities, and incremental binding energies.

The world is running out of energy, thus energy preservation is of paramount importance. Using current technology, ethylene is purified from petroleum feed stocks using the very energy intensive cryogenic distillation method. However, a purification procedure based on the redox properties of nickel bis-dithiolene complexes has been theoretically studied, in order to design a more convenient route to ethylene purification. Several possible addition routes of ethylene to neutral and anionic Ni(S2C2(CN)2)2 complexes have been modeled using density functional theory. An intraligand addition and subsequent decomposition is preferred for the neutral complex, while the interligand adduct is formed in the presence of the anion, in line with previous experimental results. The effect of the anion, whose role is as a mediator in the initial step of the reaction, is discussed, and the ability of this compound to avoid poisoning by acetylene is investigated. The results from the CN substituted complex are the...