Novel U-Shaped Systems Containing an Imide-Functionalized Cleft for the Study of Solvent-Mediated Electron Transfer and Energy Transfer: Synthesis and Binding Studies

A solution to the vexing problem of investigating solvent-mediated electron transfer under conditions of frozen solvent motion may be at hand with the synthesis of novel U-shaped systems such as 1 (R=CO(2)Me) and 2 (R=CH(2)OMe), in which the imide-functionalized cleft provides the point of attachment of the "solvent" molecule, either covalently or by hydrogen bonding.     

Modeling of Phase Separation in Alloys with Coherent Elastic Misfit

Elastic interactions arising from a difference of lattice spacing between two coherent phases can have a strong influence on the phase separation (coarsening) behavior of alloys. If the elastic moduli are different in the two phases, the elastic interactions may accelerate, slow down or even stop the phase separation process. If the material is elastically anisotropic, the precipitates can be shaped like plates or needles instead of spheres and can arrange themselves into highly correlated patterns. Tensions or compressions applied externally to the specimen may have a strong effect on the shapes and arrangement of the precipitates. In this paper, we review the main theoretical approaches that have been used to model these effects and we relate them to experimental observations. The theoretical approaches considered are (i) macroscopic models treating the two phases as elastic media separated by a sharp interface, (ii) mesoscopic models in which the concentration varies continuously across the interface, and (iii) microscopic models which use the positions of individual atoms.     

High-throughput synthesis of N3-acylated dihydropyrimidines combining microwave-assisted synthesis and scavenging techniques

[reaction: see text] The solution-phase synthesis of N3-acylated dihydropyrimidines was achieved utilizing microwave flash heating both in the synthesis (acylation) and purification (scavenging) steps. Quenching times for excess anhydrides using polystyrene or silica-supported diamine sequestration reagents were reduced from several hours to minutes utilizing microwave irradiation. The use of water as sequestration agent, coupled with an efficient solid-phase extraction workup technique allowed the rapid generation of a 20-member library of N3-acylated dihydropyrimidines.     

C2-symmetric bissulfoximines as ligands in copper-catalyzed enantioselective Diels-Alder reactions

[reaction: see text] Bissulfoximines have been used as chiral ligands in copper-catalyzed enantioselective Diels-Alder reactions between acryloyl-2-oxazolidinones and cyclopentadiene. After optimizing the ligand structure, the metal source, the counterions, and the solvent, products with up to 93% ee have been obtained.     

The cation-deficient Ruddlesden-Popper oxysulfide Y2Ti2O5S2 as a layered sulfide: topotactic potassium intercalation to form KY2Ti2O5S2

Potassium intercalation into the cation-deficient n = 2 Ruddlesden-Popper oxysulfide Y(2)Ti(2)O(5)S(2) to form KY(2)Ti(2)O(5)S(2) has been carried out by reaction of the oxysulfide with potassium vapor in sealed metal tubes at 400 degrees C, potassium naphthalide in THF at 50 degrees C, or potassium in liquid ammonia at temperatures as low as -78 degrees C. Insertion of potassium is topotactic, and although a site 12-coordinate by oxide ions is vacant in the perovskite-type oxide slabs of the structure, potassium is too large to enter this site via the 4-coordinate window, and instead enters the rock-salt-type sulfide layers of the structure which necessitates a 30% increase in the lattice parameter c normal to the layers. In contrast with one of the sodium intercalates of Y(2)Ti(2)O(5)S(2) (beta-NaY(2)Ti(2)O(5)S(2)) in which sodium occupies a tetrahedral site in the sulfide layers, potassium favors an 8-coordinate site which necessitates a relative translation of adjacent oxide slabs. KY(2)Ti(2)O(5)S(2) is tetragonal: P4/mmm, a = 3.71563(4) A, c = 14.8682(2) A (at 298 K), Z = 1. Although the resistivity (3.4(1) x 10(3) Omega cm) is larger than would be expected for a metal, temperature independent paramagnetism dominates the magnetic susceptibility, and the material is electronically very similar to the analogous sodium intercalate beta-NaY(2)Ti(2)O(5)S(2) which features reduced-titanium-containing oxide layers of very similar geometry and electron count.     

Molecular structures,bond energies,and bonding analysis of group 11 cyanides TM(CN) and isocyanides TM(NC) (TM = Cu,Ag, Au)

We report on quantum chemical calculations at the DFT (BP86/TZP) and ab initio (CCSD(T)/III+) levels of the title compounds. The geometries, vibrational spectra, heats of formation, and homolytic and heterolytic bond dissociation energies are given. The calculated bond length of Cu-CN is in reasonable agreement with experiment. The theoretical geometries for CuNC and the other group 11 cyanides and isocyanides which have not been measured as isolated species provide a good estimate for the exact values. The theoretical bond dissociation energies and heats of formation should be accurate with an error limit of +/-5 kcal/mol. The calculation of the vibrational spectra shows that the C-N stretching mode of the cyanides, which lies between 2170 and 2180 cm(-)(1), is IR inactive. The omega(1)(C-N) vibrations of the isocyanides are shifted by approximately 100 cm(-)(1) to lower wavenumbers. They are predicted to have a very large IR intensity. The nature of the metal-ligand interactions was investigated with the help of an energy partitioning analysis in two different ways using the charged fragments TM(+) + CN(-) (TM = transition metal) and the neutral fragments TM(*) + CN(*) as bonding partners. The calculations suggest that covalent interactions are the driving force for the formation of the TM-CN and TM-NC bonds, but the finally formed bonds are better described in terms of interactions between TM(+) and CN(-), which have between 73% and 80% electrostatic character. The contribution of the pi bonding is rather small. The lower energy of the metal cyanides than that of the isocyanides comes from the stronger electrostatic interaction between the more diffuse electron density at the carbon atom of the cyano ligand and the positively charged nucleus of the metal.     

Structural diversity and polytypism of lead phenylphosphonates: BING-6 and BING-9

We report the solvothermal synthesis and characterization of a series of layered lead phenylphosphonates. The crystals were suitable for single crystal X-ray diffraction data, and the two new structures we denote BING-6 [SUNY at Binghamton, Structure No. 6, Pb(PO(3)C(6)H(5)).0.25C(5)H(5)N, triclinic space group Ponemacr;, Z = 2, a = 7.0770(4) A, b = 9.3113(6) A, c = 14.6785(9) A, alpha = 80.456(1) degrees, beta = 78.023(1) degrees, gamma = 73.265(1)(o)] and BING-9 [Pb(PO(3)HC(6)H(5))(PO(3)HC(6)H(4)CH(3)), monoclinic space group C2/c, Z = 4, a = 32.663(8) A, b = 5.6220(13) A, c = 8.3307(19) A, beta = 101.419(4)(o)]. The third structure, a polytype of BING-9, was previously known only from powder X-ray diffraction methods and is denoted 3 [Pb(PO(3)HC(6)H(5))(2), monoclinic space group C2/c, Z = 4, a = 31.681(6) A, b = 5.5639(11) A, c = 8.2515(16) A, beta = 101.814(4)(o)]. All three structures possess Pb(II) and P centers connected by doubly and triply bridging oxygens. The phenyl groups cap and separate the charge-neutral layers. The phosphonates of BING-6 are nonprotonated, and the structure therefore has a Pb/P ratio of 1:1. Neutral, partially disordered pyridine solvent molecules also reside in the interlamellar space, increasing the layer to layer distance. BING-9 and 3 are polytypes and contain singly protonated phosphonates, for a Pb/P ratio of 1:2. Further characterization methods are discussed, including powder X-ray diffraction, in-situ variable temperature powder X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. Related work in the Ge, Sn, and Mn systems is also discussed. These low-dimensional materials may be useful intercalation compounds for ion-exchange or sensor applications.     

Asymmetric synthesis of oxygen heterocycles via Pd-catalyzed dynamic kinetic asymmetric transformations: application to nucleosides

Racemic butadiene and isoprene monoepoxide react with unsaturated alcohols in the presence of a chiral palladium catalyst and a boron co-catalyst to give 3-alkoxy-4-hydroxy-1-butene and 3-alkoxy-4-hydroxy-3-methyl-1-butene, respectively, with excellent regio- and enantioselectivity in a dynamic kinetic asymmetric transformation whereby both enantiomers of the starting epoxides provide the same enantiomeric product. In the case of 2-phenylbutadiene monoepoxide, easily available from phenacyl chloride and vinylmagnesium bromide, the reaction proceeds by kinetic resolution. A model to rationalize the result is presented. The bis-olefin products are ideal substrates for the Ru catalyzed ring closing metathesis. In this way, five-, six-, and seven-membered oxygen heterocycles are readily available enantiomerically pure. The value of this very simple two step process is demonstrated by the use of the five-membered ring heterocycles to form unnatural and unusual nucleosides that cannot be easily accessed by other means. The sequence involves a Ru catalyzed isomerization of the initial 2,5-dihydrofuran to a 2,3-dihydrofuran followed by a selenium promoted addition of a pyrimidine or purine base. One advantage of this strategy is the easy access to either enantiomeric series, both of which have important biological applications.