Inorganic asymmetric synthesis: diastereoselective syntheses of mono- and dinuclear complexes containing octahedral, two-bladed propeller, bis(pyridine-2-aldehyde 2'-pyridylhydrazone)iron(II) stereocenters

A C2 hexadentate diester derived from (5-hydroxymethyl)pyridine-2-aldehyde 2'-pyridylhydrazone (5-HOCH2PAPHY) and an enantiomerically pure (aS)-spirane dicarboxylic acid diastereoselectively reacts with iron(II) benzenesulfonate in methanol to furnish a 20% diastereomeric excess (de) of a two-bladed propeller, octahedral iron complex in which the P configuration of the newly created (+/-)-[Fe(PAPHY)2](2+) stereocenter predominates; when the reaction mixture is heated under reflux for 12 h, however, the excess of the diastereomer having the P configuration at iron increases to 80%, as determined by (1)H NMR spectroscopy. The configuration at iron in the major diastereomer of the complex was determined by comparison of the circular dichroism spectrum of the deprotonated complex with that of a related complex of known configuration. Repositioning of the hydroxymethyl group of the pyridine-2-aldehyde from the 5- to the 6-position produced a C2-spirane ligand that generates a double-stranded diiron(II) helicate in >99% de. Single crystal X-ray structure determinations of the racemates of the protonated and deprotonated helicates revealed that the complexes crystallize diastereoselectively, that is, two ligand strands of a S configuration generate two octahedral iron(II) stereocenters of P configuration to give a dinuclear metal helicate of P configuration and vice versa for the ligand of a R configuration.     

Aryl-bridged 1-hydroxypyridin-2-one: sensitizer ligands for Eu(III)

The synthesis, crystal structure, solution stability, and photophysical properties of an aryl group bridging two 1-hydroxypyridin-2-one units complexed to Eu(III) are reported. The results show that this backbone unit increases the rigidity of the ensuing complex, and also the conjugation of the ligand. As a result of the latter, the singlet absorption energy is decreased, along with the energy of the lowest excited triplet state. The resulting efficiency of sensitization for the Eu(III) ion is influenced by these phenomena, yielding an overall quantum yield of 6.2% in aqueous solution. The kinetic parameters arising from the luminescence data reveal an enhanced nonradiative decay rate for this compound when compared to previously reported aliphatic bridges.     

Experimental and theoretical studies of the effect of mass on the dynamics of gas/organic-surface energy transfer

The effect of mass on gas/organic-surface energy transfer is explored via investigation of the scattering dynamics of rare gases (Ne, Ar, and Kr) from regular (CH3-terminated) and omega-fluorinated (CF3-terminated) alkanethiol self-assembled monolayers (SAMs) at 60 kJmol collision energy. Molecular-beam scattering experiments carried out in ultrahigh vacuum and molecular-dynamics simulations based on high-accuracy potentials are used to obtain the rare-gases' translational-energy distributions after collision with the SAMs. Simulations indicate that mass is the most important factor in determining the changes in the energy exchange dynamics for Ne, Ar, and Kr collisions on CH3- and CF3-terminated SAMs at 60 kJmol collision energy. Other factors, such as changes in the gas-surface potential and intrasurface interactions, play only a minor role in determining the differential dynamics behavior for the systems studied.     

Morphological change of asymmetric oxyethylene/oxybutylene block copolymers induced by montmorillonite

Two oxyethylene/oxybutylene block copolymers (E(40)B(79) and E(47)B(62)), which exhibit body-centered cubic sphere (bcc) and hexagonally packed cylindrical (hex) melt morphologies in bulk, respectively, were blended with nanoclay of montmorillonite (MMT). The effects of MMT on the morphology and crystallization of E(40)B(79) and E(47)B(62) were studied with small-angle x-ray scattering, wide-angle x-ray diffraction, and differential scanning calorimeter. It is found that the E block in the block copolymers can intercalate into the galleries of MMT, leading to a larger layer spacing than that of neat MMT. The preferential absorption of the E block onto MMT plates induces the formation of a new lamellar structure, irrespectively of original morphology in the bulk. There is, however, coexistence of the new lamellar structure with regions retaining the melt morphology. The order-disorder transition temperature (T(ODT)) of the block copolymer is increased by MMT for E(40)B(79), but it remains unchanged for E(47)B(62). Crystallinity of the block copolymers is also greatly suppressed by the addition of MMT.     

Highly Unsaturated Platinum and Palladium Carbenes PtC3 and PdC3 Isolated and Characterized in the Gas Phase

Carbenes of platinum and palladium, PtC₃ and PdC₃, were generated in the gas phase through laser vaporization of a metal target in the presence of a low concentration of a hydrocarbon precursor undergoing supersonic expansion. Rotational spectroscopy and ab initio calculations confirm that both molecules are linear. The geometry of PtC₃ was accurately determined by fitting to the experimental moments of inertia of twenty‐six isotopologues. The results are consistent with the proposal of an autogenic isolobal relationship between O, Au⁺, and Pt atoms.     

Two‐ and Three‐Tiered Stacked Architectures by Covalent Assembly

Simple discotic cores functionalized with reactive arms have been assembled into two‐ and three‐tiered covalent stacks through imine formation. The targets are obtained in good yields, but competing formation of misassembled byproducts highlights some of the challenges inherent to the thermodynamically controlled assembly of rigid, compact, three‐dimensional architectures. The structures comprise a central stack of arenes surrounded by a triple helix of interconnected arms. The racemization rate is strongly dependent on the number of tiers, suggesting cooperative conformational coupling in these multi‐tiered structures.     

Platform Synthetic Lectins for Divalent Carbohydrate Recognition in Water

Biomimetic carbohydrate receptors (“synthetic lectins”) have potential as agents for biological research and medicine. However, although effective strategies are available for “all‐equatorial” carbohydrates (glucose, etc.), the recognition of other types of saccharide under natural (aqueous) conditions is less well developed. Herein we report a new approach based on a pyrene platform with polar arches extending from aryl substituents. The receptors are compatible with axially substituted carbohydrates, and also feature two identical binding sites, thus mimicking the multivalency observed for natural lectins. A variant with negative charges forms 1:2 host/guest complexes with aminosugars, with K₁>3000 m ^?1 for axially substituted mannosamine, whereas a positively charged version binds the important α‐sialyl unit with K₁≈1300 m ^?1.     

Direct Cross‐Couplings of Propargylic Diols

[Pd(PPh₃)₄] catalyzes a Suzuki–Miyaura‐like twofold cross‐coupling sequence between underivatized propargylic diols and either aryl or alkenyl boronic acids to furnish highly substituted 1,3‐dienes. Thus, 2,3‐diaryl‐1,3‐butadienes and their dialkenic congeners ([4]dendralenes) are delivered in a (pseudo)halogen‐free, single‐step synthesis which supersedes existing methods. Allenols are also readily formed. Treatment of these single‐ and twofold cross‐coupled products with acid leads to remarkably short syntheses of highly‐substituted benzofulvenes and aryl indenes, respectively.     

NIR‐to‐NIR Two‐Photon Scanning Laser Microscopy Imaging of Single Nanoparticles Doped by YbIII Complexes

The photophysical and nonlinear optical properties of water‐soluble chromophore‐functionalised tris‐dipicolinate complexes [LnL₃]^3? (Ln=Yb and Nd) are thoroughly studied, revealing that only the Yb^III luminescence can be sensitized by a two‐photon excitation process. The stability of the complex in water is strongly enhanced by embedding in dispersible organosilicate nanoparticles (NPs). Finally, the spectroscopic properties of [NBu₄]₃[YbL₃] are studied in solution and in the solid state. The high brightness of the NPs allows imaging them as single objects using a modified two‐photon microscopy setup in a NIR‐to‐NIR configuration.     

Geometry of an Isolated Dimer of Imidazole Characterised by Rotational Spectroscopy and Ab Initio Calculations

An isolated, gas‐phase dimer of imidazole is generated through laser vaporisation of a solid rod containing a 1:1 mixture of imidazole and copper in the presence of an argon buffer gas undergoing supersonic expansion. The complex is characterised through broadband rotational spectroscopy and is shown to have a twisted, hydrogen‐bonded geometry. Calculations at the CCSD(T)(F12*)/cc‐pVDZ‐F12 level of theory confirm this to be the lowest‐energy conformer of the imidazole dimer. The distance between the respective centres of mass of the imidazole monomer subunits is determined to be 5.2751(1) Å, and the twist angle γ describing rotation of one monomer with respect to the other about a line connecting the centres of mass of the monomers is determined to be 87.9(4)°. Four out of six intermolecular parameters in the model geometry are precisely determined from the experimental rotational constants and are consistent with results calculated ab initio.