Structural study of 5-methoxyfuro[3,2-e]imidazo[1,2-c]pyrimidine

The nmr and X-ray diffraction data of the novel ring system furo[3,2-e]imidazo[1,2-c]pyrimidine are reported in this paper. The crystal and molecular structure of this compound (C₉H₇N₃O₂·1/2H₂O) has been solved at room temperature. Crystals are monoclinic in a space group of P2/n with cell constants a = 9.982(8), b = 13.526(9) and c = 13.981(9) Å, β = 107.44(5)°, V = 1800.9 ų, Z = 8, D_x = 1.462 Mg·m^?3. The structure was solved by full matrix least square refinement giving a final R = 0.054 (Rw = 0.069) for 1263 reflections (I>3.0σ(I)). The compound is essentially planar, existing in two slightly structural different forms, A and B. These are held in pairs with symmetry related molecules by hydrogen bonds formed with two water molecules. Then the dimeric units are stacked parallel to the c axis to form the tridimensional packing.     

Structural optimization of enantiopure 2-cyclialkylamino-2-aryl-1,1-diphenylethanols as catalytic ligands for enantioselective additions to aldehydes

The structural optimization of a family of modular, enantiopure beta-amino alcohol ligands with a common 2-amino-2-aryl-1,1-diphenylethanol skeleton, whose stereogenicity was introduced through the Jacobsen epoxidation of 1,1-diphenyl-2-arylethylenes, has led to the identification of a small set of optimal catalysts with enhanced activity and enantioselectivity in the addition of alkylzinc and arylzinc reagents to aldehydes. Criteria for the discrimination between apparently analogous, highly enantioselective ligands are proposed.     

Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+)

Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.     

Computed coupling constants in X(CH3)nH(4-n) moieties where X = 13C and 15N+, and n = 0-4: comparisons with experimental data

Seventy-three unique spin-spin coupling constants have been analyzed for the ten species in the two series X(CH3)nH(4-n), where the central atom X is 13C or 15N+. Thirty-seven experimental values have been obtained from the literature, and several new coupling constants have been measured for the methyl-substituted ammonium ions. Both DFT with the B3LYP functional and ab initio EOM-CCSD calculations have been carried out on these same systems. Coupling constants computed by these two methods are in agreement with experimental values. Some problems related to coupling constants for the cationic ammonium systems have been resolved when these were recomputed at EOM-CCSD for complexes in which NH4+ is hydrogen-bonded to H2O molecules.     

The use of DOSY experiments to determine the solution structures of coinage metal pyrazolates: The case of {[3,5-(CF3)2Pz]Ag}3

A series of DOSY experiments have been carried out to determine the solution stoichiometry of silver(I) 3,5-bis (trifluoromethyl)pyrazolate species. This compound exists as a trimer in the solid state (n = 3) but in solutions of chlorinated solvents, the DOSY data suggest the presence of a mixture of solvent stabilized monomer (n = 1) and dimer (n = 2) in equilibrium. Different approximations have been used including the Stokes–Einstein and the Stokes–Einstein–Gierer–Wirtz equations. Some methodological problems are discussed.