DFT calculations have been carried out to study the detailed mechanism of Rh(III)-catalyzed C–H activation/cyclization of 2-acetyl-1-arylhydrazines with alkynes leading to the formation of indoles, in which the hydrazine moiety is used as the internal oxidant. The energy profiles associated with the catalytic cycle, involving N–H deprotonation, C–H activation (a concerted metalation–deprotonation (CMD) process), alkyne insertion, ring rearrangement/isomerization, and finally N–N bond cleavage/reductive elimination to regenerate the active species, are presented and analyzed. Through analysis of the calculation results, we found that the combined processes of the CMD and alkyne insertion contribute to the overall rate-determining step. The N–N bond cleavage step was examined in detail to understand how the internal oxidant interacts with the metal center to facilitate the catalytic reactions. The factor influencing regioselectivity was also investigated. How different types of substrates (alkynes versus alkenes) and internal oxidants (−NH(NHAc) versus −NH(OAc)) influence the reaction mechanisms, Rh(III)/Rh(I) versus Rh(III)/Rh(V) catalytic cycles, was discussed.

The electronic and structural properties of a series of triniobium oxide clusters, Nb 3 O n -and Nb 3 O n (n ) 3-8), are investigated using photoelectron spectroscopy (PES) and density functional theory (DFT) calculations. PES spectra are obtained for

We investigated the structures and bonding of two series of early transition-metal oxide clusters, M(2)O(n)(-) and M(2)O(n) (M = Nb, Ta; n = 5-7) using photoelectron spectroscopy (PES) and density-functional theory (DFT). The stoichiometric M(2)O(5) clusters are found to be closed shell with large HOMO-LUMO gaps, and their electron affinities (EAs) are measured to be 3.33 and 3.71 eV for M = Nb and Ta, respectively; whereas EAs for the oxygen-rich clusters are found to be much higher: 5.35, 5.25, 5.28, and 5.15 eV for Nb(2)O(6), Nb(2)O(7), Ta(2)O(6), and Ta(2)O(7), respectively. Structural searches at the B3LYP level yield triplet and doublet ground states for the oxygen-rich neutral and anionic clusters, respectively. Spin density analyses reveal oxygen radical, diradical, and superoxide characters in the oxygen-rich clusters. The M(2)O(7)(-) and M(2)O(7) clusters, which can be viewed to be formed by M(2)O(5)(-/0) + O(2), are utilized as molecular models to understand dioxygen activation on M(2)O(5)(-) and M(2)O(5) clusters. The O(2) adsorption energies on the stoichiometric M(2)O(5) neutrals are shown to be surprisingly high (1.3-1.9 eV), suggesting strong capabilities to activate O(2) by structural defects in Nb and Ta oxides. The PES data also provides valuable benchmarks for various density functionals (B3LYP, BP86, and PW91) for the Nb and Ta oxides.

The electronic and structural properties of monohafnium oxide clusters, HfO(n)(-) and HfO(n) (n = 1-6), are investigated using anion photoelectron spectroscopy and density-functional theory at the B3LYP level. The observed ground-state adiabatic detachment energy is low for HfO(-) (0.5 ± 0.1 eV) and HfO(2)(-) (2.125 ± 0.010 eV), roughly constant for HfO(3)(-) (3.6 ± 0.1 eV), HfO(4)(-) (3.67 ± 0.05 eV), and HfO(5)(-) (3.9 ± 0.1 eV), and substantially higher for HfO(6)(-) (4.9 ± 0.1 eV). Activated oxygen species, such as radical, superoxide, peroxide, diradical, and triradical, are identified in the HfO(n)(-) and HfO(n) clusters. The Hf center is shown to be flexible to accommodate the oxygen species. The sum of formal Hf-O bond orders around the Hf center is equal to four for all of the neutral clusters studied, and five for all of the anions. The O-rich HfO(n)(-) and HfO(n) (n = 3-6) clusters provide well-defined molecular models to understand O(2) adsorption and activation on an Hf center.

DFT calculations have been carried out to study the detailed mechanism of Pd-catalyzed intermolecular coupling reactions of 2-silylaryl bromides with alkynes via selective cleavage of C(sp(3))-Si bonds. Through our calculations, we found that, starting from the alkenylpalladium intermediate derived from oxidative addition of the substrate C-Br bond followed by alkyne insertion, there are two possible pathways leading to the formation of the benzosilole product. Furthermore, these two pathways were found to be competitive. In this paper, we will present the detailed mechanistic study and analyze the results we have obtained.

H 2 S is abundantly available in nature, and it is a common byproduct in industries. Molybdenum sulfides have been proved to be active in the catalytic decomposition of hydrogen sulfide (H 2 S) to produce hydrogen. In this study, density functional theory (DFT) calculations are carried out to explore the reaction mechanisms of H 2 S with MS 3 (M = Mo, W) clusters. The reaction mechanism of H 2 S with MoS 3 is roughly the same as that of the reaction with WS 3 , and the free-energy profile of the reaction with MoS 3 is slightly higher than that of the reaction with WS 3 . The overall driving forces (−ΔG) are positive, and the overall reaction barriers (ΔG b ) are rather small, indicating that such H 2 productions are product-favored. MS 3 (M = Mo, W) clusters have clawlike structures, which have electrophilic metal sites to receive the approaching H 2 S molecule. After several hydrogen-atom transfer (HAT) processes, the final MS 4 •H 2 (IM-4) complexes are formed, which could desorb H 2 at a relatively low temperature. The singlet product MS 4 clusters contain the singlet S 2 moiety, similar to the adsorbed singlet S 2 on the surface of sulfide catalysts. The theoretical results are compared with the experiments of heterogeneous catalytic decomposition of H 2 S by MoS 2 catalysts. Our work may provide some insights into the optimal design of the relevant catalysts.

Hierarchical metal oxide superstructures have been widely utilized in various applications, but complex template-assisted procedures and organic structure-directing agents are usually required during synthesis. Herein, a threedimensional (3D) bundle-like Nb 2 O 5 superstructure was fabricated by a simple hydrothermal method using amorphous Nb 2 O 5 •nH 2 O particles as precursors without the use of organic species and template precursors. Controlled experiments under different synthetic conditions revealed that a hierarchical assembly process occurred, in which Nb 2 O 5 nanorods were first formed due to the dissolution and recrystallization of Nb 2 O 5 •nH 2 O particles. The resultant nanorods were assembled into bundle-like nanostructures, which finally organized into flower-like superstructures. Upon decorating of ultrafine Pt nanoparticles (1.8 nm) on the surface of Nb 2 O 5 −S using a photodeposition method, the Pt−Nb 2 O 5 superstructures showed promising photoactivities for ethylene oxidation.

We have provided a model for understanding two isoelectronic matryoshka clusters, [Sn@Cu12@Sn20](12-) and [As@Ni12@As20](3-). By dividing each of the clusters in a layer-by-layer manner and allowing each layer to follow a simple electron-filling rule, we can formulate a consistent model to explain experimental and computed properties of both matryoshka clusters that cannot be adequately explained by existing models. By analysing these clusters in a way analogous to peeling an onion, we can not only have an understanding of the structure and bonding of the two matryoshka clusters under study, but also have a generalizable model to handle certain p/d-block@d-block endohedral clusters.