NMR Signatures and Electronic Structure of Ti Sites in Titanosilicalite-1 from Solid-State 47/49Ti NMR Spectroscopy.

Although titanosilicalite-1 (TS-1) is among the most successful oxidation catalysts used in industry, its active site structure is still debated. Recent efforts have mostly focused on understanding the role of defect sites and extraframework Ti. Here, we report the 47/49Ti signature of TS-1 and molecular analogues [Ti(OTBOS)4] and [Ti(OTBOS)3(OiPr)] using novel MAS CryoProbe to enhance the sensitivity. While the dehydrated TS-1 displays chemical shifts similar to those of molecular homologues, confirming the tetrahedral environment of Ti consistent with X-ray absorption spectroscopy, it is associated with a distribution of larger quadrupolar coupling constants, indicating an asymmetric environment. Detailed computational studies on cluster models highlights the high sensitivity of the NMR signatures (chemical shift and quadrupolar coupling constant) to small local structural changes. These calculations show that, while it will be difficult to distinguish mono- vs dinuclear sites, the sensitivity of the 47/49Ti NMR signature should enable distinguishing the Ti location among specific T site positions.

Ruthenium carbenes supported on mesoporous silicas as highly active and selective hybrid catalysts for olefin metathesis reactions under continuous flow.

In the search for a highly active and selective heterogenized metathesis catalyst, we systematically varied the pore geometry and size of various silica-based mesoporous (i.e., MCM-41, MCM-48, and SBA-15) and microporous (ZSM-5 and MWW) versus macroporous materials (D11-10 and Aerosil 200), besides other process parameters (temperature, dilution, and mean residence time). The activity and, especially, selectivity of such "linker-free" supports for ruthenium metathesis catalysts were evaluated in the cyclodimerization of cis-cyclooctene to form 1,9-cyclohexadecadiene, a valuable intermediate in the flavor and fragrance industry. The optimized material showed not only exceptionally high selectivity to the valuable product, but also turned out to be a truly heterogeneous catalyst with superior activity relative to the unsupported homogeneous complex.

The first catalytic synthesis of an acrylate from CO2 and an alkene-a rational approach.

For more than three decades the catalytic synthesis of acrylates from the cheap and abundantly available C(1) building block carbon dioxide and alkenes has been an unsolved problem in catalysis research, both in academia and industry. Herein, we describe a homogeneous catalyst based on nickel that permits the catalytic synthesis of the industrially highly relevant acrylate sodium acrylate from CO(2), ethylene, and a base, as demonstrated, at this stage, by a turnover number of greater than 10 with respect to the metal.

Organic super-acceptors with efficient intramolecular charge-transfer interactions by [2+2] cycloadditions of TCNE, TCNQ, and F4-TCNQ to donor-substituted cyanoalkynes.

Rivaling the best one: Thermal [2+2] cycloadditions of TCNE, TCNQ, and F(4)-TCNQ to N,N-dimethylanilino-substituted cyanoalkynes afforded a new class of organic super-acceptors featuring efficient intramolecular charge-transfer interactions. These acceptors rival the acceptor F(4)-TCNQ in the propensity for reversible electron uptake as well as in electron affinity (see figure), which makes them interesting as p-type dopants for potential application in optoelectronic devices.Thermal [2+2] cycloadditions of tetracyanoethene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)-TCNQ) to N,N-dimethylanilino-substituted (DMA-substituted) alkynes bearing either nitrile, dicyanovinyl (DCV; -CH==C(CN)(2)), or tricyanovinyl (TCV; -C(CN)==C(CN)(2)) functionalities, followed by retro-electrocyclization, afforded a new class of stable organic super-acceptors. Despite the nonplanarity of these acceptors, as revealed by X-ray crystallographic analysis and theoretical calculations, efficient intramolecular charge-transfer (CT) interactions between the DMA donors and the CN-containing acceptor moieties are established. The corresponding CT bands appear strongly bathochromically shifted with maxima up to 1120 nm (1.11 eV) accompanied by an end-absorption in the near infrared around 1600 nm (0.78 eV) for F(4)-TCNQ adducts. Electronic absorption spectra of selected acceptors were nicely reproduced by applying the spectroscopy oriented configuration interaction (SORCI) procedure. The electrochemical investigations of these acceptors by cyclic voltammetry (CV) and rotating disc voltammetry (RDV) in CH(2)Cl(2) identified their remarkable propensity for reversible electron uptake rivaling the benchmark compounds TCNQ (E(red,1)=-0.25 V in CH(2)Cl(2) vs. Fc(+)/Fc) and F(4)-TCNQ (E(red,1)=+0.16 V in CH(2)Cl(2) vs. Fc(+)/Fc). Furthermore, the electron-accepting power of these new compounds expressed as adiabatic electron affinity (EA) has been estimated by theoretical calculations and compared to the reference acceptor F(4)-TCNQ, which is used as a p-type dopant in the fabrication of organic light-emitting diodes (OLEDs) and solar cells. A good linear correlation exists between the calculated EAs and the first reduction potentials E(red,1). Despite the substitution with strong DMA donors, the predicted EAs reach the value calculated for F(4)-TCNQ (4.96 eV) in many cases, which makes the new acceptors interesting for potential applications as dopants in organic optoelectronic devices. The first example of a charge-transfer salt between the DMA-substituted TCNQ adduct (E(red,1)=-0.27 V vs. Fc(+)/Fc) and the strong electron donor decamethylferrocene ([FeCp*(2)]; Cp*=pentamethylcyclopentadienide; E(ox,1)=-0.59 V vs. Fc(+)/Fc) is described. Interestingly, the X-ray crystal structure showed that in the solid state the TCNQ moiety in the acceptor underwent reductive sigma-dimerization upon reaction with the donor.

Ionization and double ionization of small water clusters.

The valence ionization and double ionization spectra of the water molecule, of the water dimer, and the cyclic water clusters (H2O)3 and (H2O)4 are calculated by ab initio Green's function methods and discussed in some detail. Particular attention is paid to the analysis of the development of the spectra with increasing cluster size. Electronic decay following inner valence ionization is addressed and a crude estimate for the kinetic energy spectrum of the secondary electrons is given for the clusters.

Electronic decay following ionization of aqueous Li+ microsolvation clusters.

Ionization in the energetical range between 35 eV and 75 eV of aqueous Li(+) microsolvation clusters may initialize several different electronic decay processes. Electronic decay following H(2)O 2s ionization in a cationic cluster is reported. Li ionization probes the efficiency of electron transfer mediated decay (ETMD) processes. We report estimated ETMD lifetimes in the range of 20-100 fs for clusters with one to five water monomers. Furthermore, tertiary electron emission may occur via a combined cascade of electron transfer mediated decay and intermolecular Coulombic decay.

Mechanism of interatomic coulombic decay in clusters.

Interatomic (or intermolecular) Coulombic decay is a general, very efficient mode of decay of inner valence vacancies in clusters. The physically appealing interpretation of such decays as a transfer of a virtual photon between two cluster units rests on the neglect of the orbital overlap between them. We show that even in loosely bound van der Waals clusters the orbital overlap is a crucial factor. At the equilibrium geometry of a cluster, the overlap effect can bring about an enhancement of the decay rate by 2-3 orders of magnitude, making the process dramatically more efficient than implied by the simple estimations.