Showing papers by "Zhen Hua Li published in 2013"

Metal-Free HB(C6F5)2-Catalyzed Hydrogenation of Unfunctionalized Olefins and Mechanism Study of Borane-Mediated σ-Bond Metathesis†

Abstract: Out with the metal: Metal-free hydrogenation of unfunctionalized olefins can be achieved by employing HB(C6F5)2 as the catalyst. The key step in the catalytic reaction is believed to involve a novel borane-mediated σ-bond metathesis, which has been investigated both experimentally and theoretically.

Carbonyl bonding on oxophilic metal centers: infrared photodissociation spectroscopy of mononuclear and dinuclear titanium carbonyl cation complexes.

Abstract: Mononuclear and dinuclear titanium carbonyl cation complexes including Ti(CO)6+, Ti(CO)7+, TiO(CO)5+, Ti2(CO)9+ and Ti2O(CO)9+ are produced via a laser vaporization supersonic cluster source. The ions are mass selected in a tandem time-of-flight mass spectrometer and studied with infrared photodissociation spectroscopy in the CO stretching frequency region. The structures are established by comparison of the experimental spectra with simulated spectra derived from density functional calculations. Only one IR band is observed for the 15-electron Ti(CO)6+ cation, which is characterized to have an octahedral Oh structure. The Ti(CO)7+ cation is determined to be a weakly bound complex involving a Ti(CO)6+ core ion instead of the seventh coordinated ion. The TiO(CO)5+ cation has a completed coordination sphere with a C4v structure. The Ti2(CO)9+ cation is determined to have a doublet Cs structure with two four-electron donor side-on bridging CO groups and one semibridging CO group. The Ti2O(CO)9+ cation has a ...

Infrared photodissociation spectra of mass selected homoleptic nickel carbonyl cluster cations in the gas phase.

Abstract: Infrared spectra of mass-selected homoleptic nickel carbonyl cluster cations including dinuclear Ni2(CO)7+ and Ni2(CO)8+, trinuclear Ni3(CO)9+ and tetranuclear Ni4(CO)11+ are measured via infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The structures are established by comparison of the experimental spectra with simulated spectra derived from density functional calculations. The Ni2(CO)7+ cation is characterized to have an unbridged asymmetric (OC)4Ni–Ni(CO)3+ structure with a Ni–Ni single bond. The Ni2(CO)8+ cation has a Ni–Ni half-bonded D3d structure with both nickel centers exhibiting an 18-electron configuration. The trinuclear Ni3(CO)9+ cluster cation is determined to have an open chain like (OC)4Ni–NiCO–Ni(CO)4 structure. The tetranuclear Ni4(CO)11+ cluster cation is determined to have a tetrahedral structure with two-center and three-center bridge-bonded carbonyl units. These nickel carbonyl cluster cations all involve trigonal pyramid like Ni(CO)4 building blocks that satisfy the 18-electron configuration of the nickel centers.

Infrared photodissociation spectroscopy of mass-selected homoleptic cobalt carbonyl cluster cations in the gas phase.

Abstract: Infrared spectra of mass-selected homoleptic copper carbonyl cluster cations including dinuclear Cu2(CO)6(+) and Cu2(CO)7(+), trinuclear Cu3(CO)7(+), Cu3(CO)8(+), and Cu3(CO)9(+), and tetranuclear Cu4(CO)8(+) are measured via infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The structures are established by comparison of the experimental spectra with simulated spectra derived from density functional calculations. The Cu2(CO)6(+) cation is characterized to have an unbridged D3d structure with a Cu-Cu half bond. The Cu2(CO)7(+) cation is determined to be a weakly bound complex involving a Cu2(CO)6(+) core ion. The trinuclear Cu3(CO)7(+) and Cu3(CO)8(+) cluster cations are determined to have triangle Cu3 core structures with C2 symmetry involving two Cu(CO)3 groups and one Cu(CO)x group (x = 1 or 2). In contrast, the trinuclear Cu3(CO)9(+) cluster cation is determined to have an open chain-like (OC)3Cu-Cu(CO)3-Cu(CO)3 structure. The tetranuclear Cu4(CO)8(+) cluster cation is characterized to have a tetrahedral Cu4(+) core structure with all carbonyl groups terminally bonded.

A theoretical investigation on the influence of anatase support and vanadia dispersion on the oxidative dehydrogenation of propane to propene

Abstract: The oxidative dehydrogenation of propane (ODP) on the anatase supported vanadia catalysts (VO x /TiO 2 ) have been investigated using periodic DFT calculations. Free energy profiles indicate that the first C–H activation step is the rate-determining (RD) step and the transition state (TS) of the propene formation step is the RD–TS. ODP activity can be tuned by vanadia dispersion and support surface via the modification of the electronic structure of the active oxygen sites. For the RD step, on both dimer VO x /TiO 2 catalysts terminal sites have higher activity. On monomer VO x /TiO 2 (1 0 0) terminal and interface sites exhibit similar activity, while on monomer VO x /TiO 2 (0 0 1) interface sites have higher activity. With increasing vanadia loading, the formation of propene changes from propyl radical mechanism to a concerted propoxide one. The results suggest that TiO 2 (1 0 0) is a better support surface. Terminal and interface oxygen sites act cooperatively as the first and second C–H bond activation centers, respectively.

Ethylene polymerization by new chromium catalysts based on carborane [SSO] ligands

Abstract: Tridentate carborane [S, S, O] ligands 2a–2b [(HOC6H2R2-4,6)(CH2)SC(B10H10)C(Ph)2PS, R = tBu (2a), R = Me (2b)] were synthesized and characterized. Reaction of CrCl3(THF)3 with the sodium salts of ligands 2a and 2b afford six-coordinated chromium complexes 3a and 3b. EXAFS spectroscopy performed on complex 3a to describe the coordination chemistry of ligand 2a around chromium center. DFT calculations were also performed on complex 3a to analyze the structure. The preliminary screening results revealed that six-coordinated chromium complexes 3a–3b displayed good catalytic activities towards ethylene polymerization in the presence of modified methylaluminoxane. The effect of polymerization parameters such as cocatalyst, reaction temperature, ethylene pressure, and reaction time on polymerization behavior were investigated in detail. The polymer obtained from this homogeneous catalytic reaction has a fibroid morphology.

Extended Energy Divide-and-Conquer Method Based on Charge Conservation.

Abstract: The divide-and-conquer (DC) scheme, the most popular linear-scaling method, is very important in the quantum mechanics computation of large systems. However, when a chemical system is divided into subsystems, its covalent bonds are often broken and then capped by complementary atoms/groups. In this paper, we show that the charge transfer between subsystems and the complementary atoms/groups causes the nonconservation of the total charge of the whole system, and this is the main source of error for the computed total energy. On the basis of this finding, an extension of the many-body expansion method (energy-based divide-and-conquer, EDC) utilizing charge conservation (E-EDC) is proposed. In the E-EDC method, initially the total energies of the whole system at different many-body correction levels are computed according to the EDC scheme. The total charges of the whole system, that is, the sum of the charges of the subsystems without cap atoms/groups at different many-body correction levels, are also compu...

Formation and infrared spectroscopic characterization of three oxygen-rich BiO4 isomers in solid argon.

Abstract: The reactions of bismuth atoms and O2 have been investigated using matrix isolation infrared spectroscopy and density functional theory calculations. The ground state bismuth atoms react with dioxygen to form the BiOO and Bi(O2)2 complexes spontaneously on annealing. The BiOO molecule is characterized to be an end-on bonded superoxide complex, while the Bi(O2)2 molecule is characterized to be a superoxo bismuth peroxide complex, [Bi3+(O2–)(O22-)]. Under UV–visible light irradiation, the Bi(O2)2 complex rearranges to the more stable OBiOOO isomer, an end-on bonded bismuth monoxide-ozonide complex. The end-on-bonded OBiOOO complex further rearranges to a more stable side-on bonded OBiO3 isomer upon sample annealing. In addition, the bent bismuth dioxide anion is also formed and assigned.