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A family of chelating aryl-functionalized germylene ligands has been developed and employed in the synthesis of their corresponding 16-electron Ni 0 complexes ( PhiP DippGeAr·Ni·IPr; PhiP Dipp = {[Ph 2 PCH 2 Si( i Pr) 2 ](Dipp)N} - ; IPr = [{(H)CN(Dipp)} 2 C:]; Dipp = 2,6- i Pr 2 C 6 H 3 ). These complexes demonstrate the ability to cooperatively and reversibly activate dihydrogen at the germylene-nickel interface under mild conditions (1.5 atm H 2 , 298 K). We show that the thermodynamics of the dihydrogen activation process can be modulated by tuning the electronic nature of the germylene ligands, with an increase in the electron-withdrawing character displaying more exergonic Δ G 298 values, as ascertained through NMR spectroscopic Van't Hoff analyses for all systems. This is also shown to correlate with experimental 31 P NMR and UV/vis absorption data as well as with computationally derived parameters such as Ge-Ni bond order and Ni/Ge NPA charge, giving a thorough understanding of the modulating effect of ligand design on this reversible, cooperative bond activation reaction. Finally, the utility of this modulation was demonstrated in the catalytic dehydrocoupling of phenylsilane, whereby systems that disfavor dihydrogen activation are more efficient catalysts, aligning with H 2 -elimination being the rate-limiting step. A density functional theory analysis supports cooperative activation of the Si-H moiety in PhSiH 3 .

Single-site copper-based catalysts have shown remarkable activity and selectivity for a variety of reactions. However, deactivation by sintering in high-temperature reducing environments remains a challenge and often limits their use due to irreversible structural changes to the catalyst. Here, we report zeolite-based copper catalysts in which copper oxide agglomerates formed after reaction can be repeatedly redispersed back to single sites using an oxidative treatment in air at 550 °C. Under different environments, single-site copper in Cu-Zn-Y/deAlBeta undergoes dynamic changes in structure and oxidation state that can be tuned to promote the formation of key active sites while minimizing deactivation through Cu sintering. For example, single-site Cu 2+ reduces to Cu 1+ after catalyst pretreatment (270 °C, 101 kPa H 2 ) and further to Cu 0 nanoparticles under reaction conditions (270-350 °C, 7 kPa EtOH, 94 kPa H 2 ) or accelerated aging (400-450 °C, 101 kPa H 2 ). After regeneration at 550 °C in air, agglomerated CuO was dispersed back to single sites in the presence and absence of Zn and Y, which was verified by imaging, in situ spectroscopy, and catalytic rate measurements. Ab initio molecular dynamics simulations show that solvation of CuO monomers by water facilitates their transport through the zeolite pore, and condensation of the CuO monomer with a fully protonated silanol nest entraps copper and reforms the single-site structure. The capability of silanol nests to trap and stabilize copper single sites under oxidizing conditions could extend the use of single-site copper catalysts to a wider variety of reactions and allows for a simple regeneration strategy for copper single-site catalysts.

Activity descriptors are a powerful tool for the design of catalysts that can efficiently utilize H 2 with minimal energy losses. In this study, we develop the use of hydricity and H - self-exchange rates as thermodynamic and kinetic descriptors for the hydrogenation of ketones by molecular catalysts. Two complexes with known hydricity, HRh(dmpe) 2 and HCo(dmpe) 2 , were investigated for the catalytic hydrogenation of ketones under mild conditions (1.5 atm and 25 °C). The rhodium catalyst proved to be an efficient catalyst for a wide range of ketones, whereas the cobalt catalyst could only hydrogenate electron-deficient ketones. Using a combination of experiment and electronic structure theory, thermodynamic hydricity values were established for 46 alkoxide/ketone pairs in both acetonitrile and tetrahydrofuran solvents. Through comparison of the hydricities of the catalysts and substrates, it was determined that catalysis was observed only for catalyst/ketone pairs with an exergonic H - transfer step. Mechanistic studies revealed that H - transfer was the rate-limiting step for catalysis, allowing for the experimental and computation construction of linear free-energy relationships (LFERs) for H - transfer. Further analysis revealed that the LFERs could be reproduced using Marcus theory, in which the H - self-exchange rates for the HRh/Rh + and ketone/alkoxide pairs were used to predict the experimentally measured catalytic barriers within 2 kcal mol -1 . These studies significantly expand the scope of catalytic reactions that can be analyzed with a thermodynamic hydricity descriptor and firmly establish Marcus theory as a valid approach to develop kinetic descriptors for designing catalysts for H - transfer reactions.

A longstanding challenge in catalysis by noble metals has been to understand the origin of enhancements of rates of hydrogen transfer that result from the bonding of oxygen near metal sites. We investigated structurally well-defined catalysts consisting of supported tetrairidium carbonyl clusters with single-atom (apical iridium) catalytic sites for ethylene hydrogenation. Reaction of the clusters with ethylene and H 2 followed by O 2 led to the onset of catalytic activity as a terminal CO ligand at each apical Ir atom was removed and bridging dioxygen ligands replaced CO ligands at neighboring (basal-plane) sites. The presence of the dioxygen ligands caused a 6-fold increase in the catalytic reaction rate, which is explained by the electron-withdrawing capability induced by the bridging dioxygen ligands, consistent with the inference that reductive elimination is rate-determining. Electronic-structure calculations demonstrate an additional role of the dioxygen ligands, changing the mechanism of hydrogen transfer from one involving equatorial hydride ligands to that involving bridging hydride ligands. This mechanism is made evident by an inverse kinetic isotope effect observed in ethylene hydrogenation reactions with H 2 and, alternatively, with D 2 on the cluster incorporating the dioxygen ligands and is a consequence of quasi-equilibrated hydrogen transfer in this catalyst. The same mechanism accounts for rate enhancements induced by the bridging dioxygen ligands for the catalytic reaction of H 2 with D 2 to give HD. We posit that the mechanism involving bridging hydride ligands facilitated by oxygen ligands remote from the catalytic site may have some generality in catalysis by oxide-supported noble metals.

The human copper-binding protein metallothionein-3 (MT-3) can reduce Cu(II) to Cu(I) and form a polynuclear Cu(I) 4 -Cys 5-6 cluster concomitant with intramolecular disulfide bonds formation, but the cluster is unusually inert toward O 2 and redox-cycling. We utilized a combined array of rapid-mixing spectroscopic techniques to identify and characterize the transient radical intermediates formed in the reaction between Zn 7 MT-3 and Cu(II) to form Cu(I) 4 Zn(II) 4 MT-3. Stopped-flow electronic absorption spectroscopy reveals the rapid formation of transient species with absorption centered at 430-450 nm and consistent with the generation of disulfide radical anions (DRAs) upon reduction of Cu(II) by MT-3 cysteine thiolates. These DRAs are oxygen-stable and unusually long-lived, with lifetimes in the seconds regime. Subsequent DRAs reduction by Cu(II) leads to the formation of a redox-inert Cu(I) 4 -Cys 5 cluster with short Cu-Cu distances (<2.8 Å), as revealed by low-temperature (77 K) luminescence spectroscopy. Rapid freeze-quench Raman and electron paramagnetic resonance (EPR) spectroscopy characterization of the intermediates confirmed the DRA nature of the sulfur-centered radicals and their subsequent oxidation to disulfide bonds upon Cu(II) reduction, generating the final Cu(I) 4 -thiolate cluster. EPR simulation analysis of the radical g - and A -values indicate that the DRAs are directly coupled to Cu(I), potentially explaining the observed DRA stability in the presence of O 2 . We thus provide evidence that the MT-3 Cu(I) 4 -Cys 5 cluster assembly process involves the controlled formation of novel long-lived, copper-coupled, and oxygen-stable disulfide radical anion transient intermediates.

Many crystalline materials form polymorphs and undergo solid-solid transitions between different forms as a function of temperature or pressure. However, there is still a poor understanding of the mechanism of transformation. Conclusions about the transformation process are typically drawn by comparing the crystal structures before and after the conversion, but gaining detailed mechanistic knowledge is strongly impeded by the generally fast rate of these transitions. When the crystal morphology does not change, it is assumed that crystallinity is maintained throughout the process. Here we report transformation between polymorphs of ZnCl 2 (1,3-diethylimidazole-2-thione) 2 which are sufficiently slow to allow unambiguous assignment of single crystal to single crystal transformation with shape preservation proceeding through an amorphous intermediate phase. This result fundamentally challenges the commonly accepted views of polymorphic phase transition mechanisms.

Surface impurities involving parasitic reactions and gas evolution contribute to the degradation of high Ni content LiNi x Mn y Co z O 2 (NMC) cathode materials. The transient kinetic technique of temporal analysis of products (TAP), density functional theory, and infrared spectroscopy have been used to study the formation of surface impurities on varying nickel content NMC materials (NMC811, NMC622, NMC532, NMC433, NMC111) in the presence of CO 2 and H 2 O. CO 2 reactivity on a clean surface as characterized by CO 2 conversion rate in the TAP reactor follows the order: NMC811 > NMC622 > NMC532 > NMC433 > NMC111. The capacity of CO 2 uptake follows a different order: NMC532 > NMC433 > NMC622 > NMC811 > NMC111. Moisture pretreatment slows down the direct CO 2 adsorption process and creates additional active sites for CO 2 adsorption. Electronic structure calculations predict that the (012) surface is more reactive than the (1014) surface for CO 2 and H 2 O adsorption. CO 2 adsorption leading to carbonate formation is exothermic with formation of ion pairs. The average CO 2 binding energies on the different materials follow the CO 2 reactivity order. Water hydroxylates the (012) surface and surface OH groups favor bicarbonate formation. Water creates more active sites for CO 2 adsorption on the (1014) surface due to hydrogen bonding. The composition of surface impurities formed in ambient air exposure is dependent on water concentration and the percentage of different crystal planes. Different surface reactivities suggest that battery performance degradation due to surface impurities can be mitigated by precise control of the dominant surfaces in NMC materials.

The rational design of multifunctional catalysts that use non-noble metals to facilitate the interconversion between H 2 , O 2 , and H 2 O is an intense area of investigation. Bimetallic nanosystems with highly tunable electronic, structural, and catalytic properties that depend on their composition, structure, and size have attracted considerable attention. Herein, we report the synthesis of bimetallic nickel-copper (NiCu) alloy nanoparticles confined in a sp 2 carbon framework that exhibits trifunctional catalytic properties toward hydrogen evolution (HER), oxygen reduction (ORR), and oxygen evolution (OER) reactions. The electrocatalytic functions of the NiCu nanoalloys were experimentally and theoretically correlated with the composition-dependent local structural distortion of the bimetallic lattice at the nanoparticle surfaces. Our study demonstrated a downshift of the d-band of the catalysts that adjusts the binding energies of the intermediate catalytic species. XPS analysis revealed that the binding energy for Ni 2p 3/2 band of the Ni 0.25 Cu 0.75 /C nanoparticles was shifted ∼3 times compared to other bimetallic systems, and this was correlated to the high electrocatalytic activity observed. Interestingly, the bimetallic Ni 0.25 Cu 0.75 /C catalyst surpassed the OER performance of RuO 2 benchmark catalyst exhibiting a small onset potential of 1.44 V vs RHE and an overpotential of 400 mV at 10 mA·cm -2 as well as the electrochemical long-term stability of commercial RuO 2 and Pt catalysts and kept at least 90% of the initial current applied after 20 000 s for the OER/ORR/HER reactions. This study reveals significant insight about the structure-function relationship for non-noble bimetallic nanostructures with multifunctional electrocatalytic properties.

The anionic ring-opening copolymerization of N-( p-tolylsulfonyl)azetidine ( pTsAzet) and N-( o-tolylsulfonyl)azetidine ( oTsAzet) produces poly( pTsAzet- co- oTsAzet) as a statistical copolymer. The pTsAzet/ oTsAzet copolymerization is living and allows for the synthesis of poly(sulfonylazetidine) of target molecular weights with narrow dispersities. 1 H NMR spectroscopy was used to monitor the kinetics of the polymerization and estimate the monomer reactivity ratios. It was found that the reactivity ratios for oTsAzet and pTsAzet at 180 °C are 1.66 and 0.60, respectively. The tosyl groups of p( pTsAzet- co- oTsAzet) were reductively removed to produce linear poly(trimethylenimine) (LPTMI). This represents the first route to LPTMI of controlled molecular weight and low dispersity. Finally, the slow kinetics of the sulfonylazetidine polymerization facilitated the synthesis of a block copolymer without requiring the sequential addition of monomer. Specifically, pTsAzet, oTsAzet, and ( N- p-toluenesulfonyl-2-methylaziridine) ( pTsMAz) were combined in solution. pTsMAz selectively polymerizes to form the first block at moderate temperature. After consumption of pTsMAz, the temperature was increased to copolymerize pTsAzet and oTsAzet and produce the block copolymer p( pTsMAz)- b-p( pTsAzet- co- oTsAzet).

The least stable isomer of the parental BN naphthalene series has been synthesized in a simple four-step sequence. Its experimental electronic structure characterization via UV-PES, cyclic voltammetry, and UV-vis spectroscopy in direct comparison with three other known BN naphthalene isomers has established two guiding principles for predicting the electronic structures of BN acene compounds: (1) Orientational BN isomers have similar HOMO-LUMO gaps. (2) For each pair of orientational BN isomers, the more thermodynamically stable compound has the lower HOMO energy. Furthermore, we demonstrate that BN/CC isosterism in the context of BN-9,1-Naph can impact crystal packing to favor a cofacial π-stack motif.

Four perfluoroalkyl cobalt(III) fluoride complexes have been synthesized and characterized by elemental analysis, multinuclear NMR spectroscopy, X-ray crystallography, and powder X-ray diffraction. The remarkable cobalt fluoride (19)F NMR chemical shifts (-716 to -759 ppm) were studied computationally, and the contributing paramagnetic and diamagnetic factors were extracted. Additionally, the complexes were shown to be active in the catalytic fluorination of p-toluoyl chloride. Furthermore, two examples of cobalt(III) bis(perfluoroalkyl)complexes were synthesized and their reactivity studied. Interestingly, abstraction of a fluoride ion from these complexes led to selective formation of cobalt difluorocarbene complexes derived from the trifluoromethyl ligand. These electrophilic difluorocarbenes were shown to undergo insertion into the remaining perfluoroalkyl fragment, demonstrating the elongation of a perfluoroalkyl chain arising from a difluorocarbene insertion on a cobalt metal center. The reactions of both the fluoride and bis(perfluoroalkyl) complexes provide insight into the potential catalytic applications of these model systems to form small fluorinated molecules as well as fluoropolymers.

Developing high-efficiency, durable, and low-cost catalysts based on earth-abundant elements for the oxygen evolution reaction (OER) is essential for renewable energy conversion and energy storage devices. In this study, we report a highly active nanostructured electrode, NanoCOT, which contains carbon, oxygen, and titanium, for efficient OER in alkaline solution. The NanoCOT electrode is synthesized from carbon transformation of TiO2 in an atmosphere of methane, hydrogen, and nitrogen at a high temperature. The NanoCOT exhibits enhanced OER catalytic activity in alkaline solution, providing a current density of 1.33 mA/cm(2) at an overpotential of 0.42 V. This OER current density of a NanoCOT electrode is about 4 times higher than an oxidized Ir electrode and 15 times higher than a Pt electrode because of its nanostructured high surface area and favorable OER kinetics. The enhanced catalytic activity of NanoCOT is attributed to the presence of a continuous energy band of the titanium oxide electrode with predominantly reduced defect states of Ti (e.g., Ti(1+), Ti(2+), and Ti(3+)) formed by chemical reduction with hydrogen and carbon. The OER performance of NanoCOT can also be further enhanced by decreasing its overpotential by 150 mV at a current density of 1.0 mA/cm(2) after coating its surface electrophoretically with 2.0 nm IrOx nanoparticles.

Near-infrared (NIR) lasers are key components for applications, such as telecommunication, spectroscopy, display, and biomedical tissue imaging. Inorganic III-V semiconductor (GaAs) NIR lasers have achieved great successes but require expensive and sophisticated device fabrication techniques. Organic semiconductors exhibit chemically tunable optoelectronic properties together with self-assembling features that are well suitable for low-temperature solution processing. Major blocks in realizing NIR organic lasing include low stimulated emission of narrow-bandgap molecules due to fast nonradiative decay and exciton-exciton annihilation, which is considered as a main loss channel of population inversion for organic lasers under high carrier densities. Here we designed and synthesized the small organic molecule (E)-3-(4-(di-p-tolylamino)phenyl)-1-(1-hydroxynaphthalen-2-yl)prop-2-en-1-one (DPHP) with amphiphilic nature, which elaborately self-assembles into micrometer-sized hemispheres that simultaneously serves as the NIR emission medium with a photoluminescence quantum efficiency of ∼15.2%, and the high-Q (∼1.4 × 10(3)) whispering gallery mode microcavity. Moreover, the radiative rate of DPHP hemispheres is enhanced up to ∼1.98 × 10(9) s(-1) on account of the exciton-vibrational coupling in the solid state with the J-type molecular-coupling component, and meanwhile the exciton-exciton annihilation process is eliminated. As a result, NIR lasing with a low threshold of ∼610 nJ/cm(2) is achieved in the single DPHP hemisphere at room temperature. Our demonstration is a major step toward incorporating the organic coherent light sources into the compact optoelectronic devices at NIR wavelengths.

The first general late-stage functionalization of monocyclic 1,2-azaborines at the C(6) position is described. Ir-catalyzed C-H borylation occurs regioselectively at the C(6) position of B-substituted 1,2-azaborines and is compatible with a range of substitution patterns at boron (e.g., hydride, alkoxide, alkyl, and aryl substituents). Subsequent Suzuki cross coupling with aryl- and heteroaryl bromides furnishes 1,2-azaborine-based biaryl compounds including 6-[pyrid-2-yl]-1,2-azaborines that represent novel κ(2)-N,N-bidentate ligands. The 6-[pyrid-2-yl]-B-Me-1,2-azaborine ligand has been demonstrated to form an emissive coordination complex with dimesitylboron that exhibits bathochromically shifted absorption and emission maxima and a higher photoluminescence quantum yield compared to its carbonaceous analogue.

The organophosphate class of compounds includes common herbicides as well as highly toxic nerve gases whose detection is important from an environmental and a public safety perspective. We describe here a fluorescence turn-on sensor array for the rapid detection and quantitation of relevant organophosphates in neutral water. The array elements self-assemble from commercially available dyes and PAMAM dendrimers, and sensing is based on an indicator displacement assay. Data interpretation through pattern recognition methods (PCA, LDA) showed excellent cluster separation and sample classification. In addition, we were also able to use this system for simultaneous differentiation and quantitative analysis of methylphosphonate (a nerve gas byproduct), glyphosate (a ubiquitous herbicide), and inorganic phosphate over a wide range of concentrations (10 μM to 2 mM).

Layered materials with controlled thickness down to monolayer are being intensively investigated for unraveling and harnessing their dimension-dependent properties. Copper antimony sulfide (CuSbS2) is a ternary layered semiconductor material that has been considered as an absorber material in thin film solar cells due to its optimal band gap (∼1.5 eV) with high absorption coefficient of over >10(4) cm(-1). We have for the first time developed solution-based approaches for the synthesis of mono-, few-, and multiple layers of CuSbS2. These include a colloidal bottom-up approach for the synthesis of CuSbS2 nanoplates with thicknesses from six layers to several layers, and a hybrid bottom-up-top-down approach for the formation of CuSbS2 mesobelts. The latter can be exfoliated by Li-ion intercalation and sonication to obtain layers down to monolayer thickness. Time-dependent TEM studies provide important insights into the growth mechanism of mesobelts. At the initial stage the nanoplates grow laterally to form nanosheets as the primary structure, followed by their folding and attachment through homoepitaxy to form prolate-like secondary structures. Eventually, these prolate-like structures form mesocrystals by oriented attachment crystal growth. The changes in optical properties with layer thickness down to monolayers have been studied. In order to understand the thickness-dependent optical and electrical properties, we have calculated the electronic structures of mono- and multiple layers (bulk) of CuSbS2 using the hybrid functional method (HSE 06). We find that the monolayers exhibit noticeably different properties from the multilayered or the bulk system, with a markedly increased band gap that is, however, compromised by the presence of localized surface states. These localized states are predominantly composed of energetically favorable Sb pz states, which break off from the rest of the Sb p states that would otherwise be at the top of the gap. The developed solution-based synthesis approaches are versatile and can likely be extended to other complex layered sulfides.

Dark-field scattering spectroelectrochemistry is used to analyze the electrochemical formation of individual Ag nanoparticles (NPs) at the surface of an indium tin oxide electrode. Heterogeneities in redox potentials among NPs not visible in bulk electrochemical measurements are presented for the first time. Through correlated electron microscopy, single NP light scattering intensity is related to particle size according to Mie theory, enabling rapid particle size determination and the construction of voltammetric curves for individual NPs.

Nanocrystals and nanoclusters of the room-temperature magnetic spinel CuCr(2)S(4) have been synthesized using a facile solution-based method. The synthesis involves hot injection of an excess of 1-dodecanethiol (1-DDT) into a boiling coordinating solvent containing CuCl(2) and CrCl(3)·6H(2)O. Using octadecylamine (ODA) as a solvent yields cube-shaped nanocrystals with an average size of 20 ± 2 nm, while with oleylamine (OLA), nanoclusters with an average size of 31 ± 2.5 nm are obtained. In both cases, powder X-ray diffraction patterns confirmed the formation of the pure spinel phase without any impurities. While the synthesized powders are superparamagnetic near room temperature, they exhibit ferromagnetic behavior at lower temperatures, with magnetization (M(S)) values of 30 emu/g (1.63 μ(B)/f.u.) and 33 emu/g (1.79 μ(B)/f.u.) for the ODA- and OLA-capped nanocrystals and nanoclusters, respectively, at 5 K., (© 2011 American Chemical Society)

The molecule (C═C)TTP (TTP = tetra-p-tolylporphyrin) and the triflate salt of its dication, [(C═C)TTP][OTf](2), have been synthesized and characterized. NMR spectroscopy, nucleus-independent chemical shift calculations, and the crystal structure of (C═C)TTP indicate that (C═C)TTP is antiaromatic and (C═C)TTP(2+) is aromatic.

Monodisperse wurtzite CuIn(x)Ga(1-x)S(2) nanocrystals have been synthesized over the entire composition range using a facile solution-based method. Depending on the chemical composition and synthesis conditions, the morphology of the nanocrystals can be controlled in the form of bullet-like, rod-like, and tadpole-like shapes. The band gap of the nanocrystals increases linearly with increasing Ga concentration, with band gap values for the end members being close to those observed in the bulk. Colloidal suspensions of the nanocrystals are attractive for use as inks for low-cost fabrication of thin film solar cells by spin or spray coating.

Ordered ZnS and CdS nanocrystal assemblies have been synthesized by a facile bioinspired approach consisting of an initial self-assembly of engineered proteins into spherical biotemplates and a subsequent protein-directed nucleation and growth of ZnS and CdS nanocrystals symmetrically distributed over the self-assembled biotemplates.

Novel shape- and structural-controlled superparamagnetic nanostructures composed of self-supported spherical and rod-like CoFe(2)O(4) colloidal nanocrystals have been prepared by thermolysis of a stoichiometric Co(2+)Fe(2)(3+)-oleate complex in organic solution with periodic injection of hexane for controlling the nucleation, assembly, and growth of the nuclei.

AFM/KPM charging and charge mapping of polyamine charge carriers in a PMMA matrix is reported. Selective charging of the designed charge carrier is demonstrated at concentrations down to a single molecule. This works constitutes electrochemical charging and detection of single redox-active organic molecules in low dielectric matrices by probe microscopy.

The first definitive high-resolution single-crystal X-ray structure for the coordination of the 1-methylimidazole (Meimid) ligand to UO2(Ac)2 (Ac = CH3CO2) is reported. The crystal structure evidence is confirmed by IR, Raman, and UV-vis spectroscopic data. Direct participation of the nitrogen atom of the Meimid ligand in binding to the uranium center is confirmed. Structural analysis at the DFT (B3LYP) level of theory showed a conformational difference of the Meimid ligand in the free gas-phase complex versus the solid state due to small energetic differences and crystal packing effects. Energetic analysis at the MP2 level in the gas phase supported stronger Meimid binding over H2O binding to both UO2(Ac)2 and UO2(NO3)2. In addition, self-consistent reaction field COSMO calculations were used to assess the aqueous phase energetics of combination and displacement reactions involving H2O and Meimid ligands to UO2R2 (R = Ac, NO3). For both UO2(NO3)2 and UO2(Ac)2, the displacement of H2O by Meimid was predicted to be energetically favorable, consistent with experimental results that suggest Meimid may bind uranyl at physiological pH. Also, log(Knitrate/KAc) calculations supported experimental evidence that the binding stoichiometry of the Meimid ligand is dependent upon the nature of the reactant uranyl complex. These results clearly demonstrate that imidazole binds to uranyl and suggest that binding of histidine residues to uranyl could occur under normal biological conditions.

A bimetallic carbene complex architecture that incorporates a cyclopentadienyl-annulated imidazol-2-ylidene moiety is characterized. The ligand architecture enables direct electronic interaction between the pi- and sigma-bonded metals. A preliminary example of aqueous Suzuki coupling employing a metallocene-fused imidazol-2-ylidene-derived catalyst is described.

Atomization energies at 0 K and heats of formation at 0 and 298 K are predicted for XeF(+), XeF(-), XeF(2), XeF(4), XeF(5)(-), and XeF(6) from coupled cluster theory (CCSD(T)) calculations with new correlation-consistent basis sets for Xe. To achieve near chemical accuracy (+/-1 kcal/mol), up to four corrections were added to the complete basis set binding energies based on frozen core coupled cluster theory energies: a correction for core-valence effects, a correction for scalar relativistic effects, a correction for first-order atomic spin-orbit effects, and in some cases, a second-order spin-orbit correction. Vibrational zero-point energies were computed at the coupled cluster level of theory. The structure of XeF(6) is difficult to obtain with the C(3)(v)() and O(h)() structures having essentially the same energy. The O(h)() structure is only 0.19 kcal/mol below the C(3)(v)() one at the CCSD(T)/CBS level using an approximate geometry for the C(3)(v)() structure. With an optimized C(3)(v)() geometry, the C(3)(v)() structure would probably become slightly lower in energy than the O(h)() one. The calculated heats of formation for the neutral XeF(n)() fluorides are less negative than the experimental values from the equilibrium measurements by 2.0, 7.7, and 12.2 kcal/mol for n = 2, 4, and 6, respectively. For the experimental values, derived from the photoionization measurements, this discrepancy becomes even larger, suggesting a need for a redetermination of the experimental values. Evidence is presented for the fluxionality of XeF(6) caused by the presence of a sterically active, free valence electron pair on Xe.

A convergent synthesis of (+)-asteltoxin (1) has been achieved by the Horner-Emmons olefination of bis(tetrahydrofuran) aldehyde 53 and alpha-pyrone phosphonate 5. A key step features the stereoselective construction of a sterically congested quaternary center embedded in the densely functionalized bis(tetrahydrofuran) subunit by a Lewis acid-catalyzed, pinacol-type rearrangement of an epoxy silyl ether. This pivotal rearrangement methodology parallels the proposed biosynthetic pathway of 1 and is ripe for applications to the stereocontrolled synthesis of structurally complex natural products.

A new approach to isoprostanes and neuroprostanes featuring cis-dialkyl stereochemistry at the cyclopentane ring has been developed by employing an intramolecular cross-coupling reaction of an alkyl iodide and a tethered alkenylsiloxane for stereoselective installation of a functionalized omega-side chain.

We report here initial results that demonstrate that cellulose can be dissolved without activation or pretreatment in, and regenerated from, 1-butyl-3-methylimidazolium chloride and other hydrophilic ionic liquids. This may enable the application of ionic liquids as alternatives to environmentally undesirable solvents currently used for dissolution of this important bioresource.

A unified, ready access to the tropoloisoquinoline alkaloids imerubrine (1), grandirubrine (2), and isoimerubrine (3) is delineated and features sequential application of the intramolecular Diels-Alder reaction of an acetylene-tethered oxazole and the [4 + 3] cycloaddition of an oxyallyl. A regioselective synthesis of 1 was achieved by stereo- and regioselective oxidation of an 8-oxabicyclo[3.2.1]oct-6-en-3-one cycloadduct by means of the Moriarty method. Such a post-cycloaddition functionalization complements the synthetic utility of an alpha-alkoxy-substituted oxyallyl so as to broaden the scope of the oxyallyl [4 + 3] cycloaddition reaction.