Chemistry - A European Journal

An iridium complex with nonconjugated cyclometalated ligands can serve as a deep-blue dopant emitter of PhOLED and the host material of PhOLED; the latter is best exemplified by efficient triplet-state energy transfer to the green-emitting [Ir(ppy)₃] (ppyH=2-phenylpyridine). In their Full Paper on page 5423 ff., Y. Chi, P.-T. Chou, C.-C. Wu et al. investigate a series of iridium complexes and discuss their phosphorescent properties.

Enantioselective catalysis employing gold(I) complexes was, until recently, exceedingly rare, due in large part to the pronounced tendency of gold(I) to form linear, two-coordinate complexes. However, new approaches and strategies have emerged over the past two years, leading to the development of a number of effective gold(I)-catalyzed enantioselective transformations, most notably the enantioselective hydrofunctionalization of allenes.

Chemical hand-waving: Dynamic molecular motion between two distinct structures (contraction/extension) is displayed by an octahedral cobalt complex (shown schematically), in which the distance between two coordinated methoxy oxygen atoms changed from 0.3 to 1.3 nm. Furthermore, the helical direction of the extended complex was inverted in response to NO₃⁻ ions, and stretching and inverting motions occurred reversibly and repeatedly.

Werner complexes go organic! When orange aqueous solutions of [Co(1,2-diamine)₃]X₃ (X=I, Cl) are treated with solutions of NaBAr_f in CH₂Cl₂ (1:3 mol ratio), the aqueous phases decolorize (see scheme) and [Co(1,2-diamine)₃](BAr_f)₃⋅nH₂O can be isolated from the CH₂Cl₂ phases (78–89 %). The ethylenediamine complex can catalyze enantioselective Michael additions, presumably by an outer-coordination-sphere mechanism involving hydrogen bonding.

Adding up carbene ligands: The unusual addition of some nucleophiles to a CO ligand of Fischer aryl carbene complexes has been developed and represents a novel and efficient approach to achieve once again the CO ligand → carbene ligand conversion. The potential of this methodology for the stereoselective synthesis of electron-rich 1,3-dienes is presented (see scheme).

Acid-catalyzed and thermal cyclization of an isolable vinyl ortho-quinone methide has been kinetically and computationally investigated. We propose that both reactions proceed through rate-limiting exo-alkylidene bond isomerization followed by faster oxa-6π electrocyclization. The vinyl ortho-quinone methide was found to be surprisingly basic, allowing for quantitative protonation with relatively weak acids. In addition, we have identified a new mode of Diels–Alder dimerization of vinyl ortho-quinone methides.

The significant problem of nerve gas poisoning requires new methods of detection that are sensitive and selective. A new G-type agent chemical sensor is reported that exploits terpyridine–lanthanide emission (see graphic). A detection limit of 6 ppb is obtained and the selectivity for reactive surrogates over a variety of other close chemical analogues is demonstrated.

Silicon science: Seen here is a new representative of the very rare clathrate III family, which exhibits the highest reported thermal stability for this class of materials; Si₁₃₀P₄₂Te₂₁ decomposes above 1500 K. The crystal structure features a special packing of large polyhedra, Te@(Si/P)_n, never observed before for cationic clathrates. Despite the structural complexity, the composition of the novel clathrate is in accordance with the Zintl rule.

True blue: The nonconjugated nature of a methylene spacer interrupts the π conjugation of the cyclometalated ligands, which lowers the π orbital energies and destabilizes the respective π* orbitals. Incorporation of a third chelating chromophore with a blue-light energy gap induces true-blue-light emission at room temperature (see figure).

Crowd trouble: Single-walled carbon nanotubes (SWNTs) can drive i-motif formation under cell-mimic crowding conditions and cause more water to be released (see figure). This indicates that SWNTs may have the potential to modulate human telomeric DNA structures in vivo, which shows the potential for drug design and cancer therapy, as it has been shown that SWNTs modulate DNA B–A transitions and B–Z changes in live cells.

Chain-end control: Bis(guanidinate) alkoxide Group 3 metal complexes (OR=OtBu, OiPr; Ln=Y, Nd, Sm, Lu) promote the stereoselective ring-opening polymerization (ROP) of rac-β-butyrolactone to form syndiotactic poly(hydroxybutyrate) through a chain-end control mechanism (see scheme), while these complexes are essentially non-stereoselective for the ROP of lactide (PLA=polylactide, PHB=poly(hydroxy-3-butyrate)).

A general model of the mass transport within tubular nanopores of mesoporous particles is developed to understand the delicate interplay between diffusion of target species and their adsorption/reaction at nanopore walls and to provide a theoretical support for optimisation of the functionality of nanoporous materials (see figure).

The π-face donation between a coplanar N-aryl group and the RuCHPh unit represents a new quality of N-heterocyclic carbenes in metal complexes (see scheme) and is described in detail herein.

Flexible, yet firm: The Mn(4)-containing sidearm on the right is highly flexible, whereas the CaMn₃ tetrahedron on the left is rigid and robust. This is one of several conclusions drawn from our calculations on possible models of the photosystem II water oxidising complex.

The first Fe^VIdioxo complex, trans-[Fe(O)₂(NH₃)₂(NMeH₂)₂]²⁺ has been generated in silico and was detected to have a reduction potential of +1.30 V (vs. NHE). [Fe(qpy)O₂]²⁺ was also detected in the gas phase by high-resolution ESI-MS spectroscopy. The picture shows the model complex and the MO diagram of its singlet d² ground state. qpy=2,2′:6′,2′′:6′′,2′′′:6′′′,2′′′′-quinquepyridine

The mechanisms of polymerization of ε-caprolactone (CL) initiated by either the rare-earth hydride [Cp₂Eu(H)] or the borohydrides [(L_x)Eu(BH₄)] (Cp=η⁵-C₅H₅) were studied at the DFT level. In all cases, hydride transfer from the rare-earth initiator to the carbonyl carbon of the lactone is followed by ring-opening of the monomer (see scheme). However, in the last step a difference is observed between the hydride and borohydride complexes.

Go to excess! The enantioselective reactions of lithiated benzyl trifluoromethyl sulfones with a substoichiometric amount of a bis(oxazoline) and various aldehydes is disclosed (see scheme). The products were formed with excellent diastereo- and high enantioselectivities. Fluorination of the sulfones with N-fluorobenzenesulfonimide and a stoichiometric amount of a bis(oxazoline) gave products with extremely high enantioselectivities (up to 99 % ee; ee= enantiomeric excess).

Strike gold: A series of newly designed ascorbic acid based, room-temperature ionic liquids were synthesized and used to prepare quasi-spherical and anisotropic gold nanostructures in aqueous medium (see figure).

My kingdom for Aphos: An aromatic amide-derived phosphane (Aphos) library is generated by using the Suzuki reaction without an added ligand (see scheme), which allows in situ screening of the new Aphos activity by using the reference coupling reaction.

Alcohol makes the difference! Alcohols are shown to be superior solvents for the Heck reaction of electron-rich olefins. Requiring neither halide scavengers nor ionic additives, various electron-rich olefins have been arylated with aryl bromides in 2-propanol and ethylene glycol with excellent rates and regioselectivities at a palladium loading of as low as 0.1 %. Hydrogen bonding appears to play an essential role in guiding the regioselectivity.

Unexpected bridges: Degradation of tetrachlorocatechol to chloranilic acid is mediated by a copper(II) complex of the tripodal, tridentate N,N,O ligand 3,3-bis(1-methylimidazol-2-yl)propionate. This unprecedented oxidative double dehalogenation of tetrachlorocatechol afforded a dicopper(II) complex with a bridging bis-bidentate chloranilato ligand (see picture).

Backfolded ion pairs and aggregates at the dendrimer termini are formed by water-soluble benzoate-terminated polyanionic dendrimers of four generations with three biologically relevant cations (acetylcoline, benzyltriethylammonium, and dopamine) according to ¹H NMR studies and determination of association constants. In the water-soluble assemblies, each carboxylate terminus reversibly interacts with two cations and a chloride ion, as shown schematically in the picture.

A good solution: A hydrogen-bonding network with 2-propanol promoted by a RuNH₂ linkage leads to the alcohol adduct Ru–alkoxide [Ru(OiPr)(CNN)(dppb)]⋅n iPrOH (HCNN=6-(4-methylphenyl)-2-pyridylmethylamine, dppb=bis(diphenylphosphino)butane), which quickly equilibrates with the hydride [Ru(H)(CNN)(dppb)] through a solvent-mediated route. The reaction of [Ru(OiPr)(CNN){(S,S)-Skewphos}]⋅n iPrOH (1) with a prochiral ketone affords the diastereomer alkoxides 2/3 with a diastereoisomeric excess equal to the enantiomeric excess of the alcohol formed in catalysis (see scheme).

Salt formation with a bang: Several new high-nitrogen salts with nitroimino-containing mono- and dianions and the dinitrocyclopentanetrione dianion have properties comparable to those of commonly used energetic materials (see picture). 4,6-Bis(nitroimino)-1,3,5-triazinan-2-one (DNAM) salts exhibit the highest heats of formation and detonation properties.

One ring less: [4]Circulene (right structure) is not only a more strongly curved hydrocarbon, but also has a smaller diameter than corannulene (left structure). If it could be used as a cap for nanotubes, these should be “slimmer” than the usual corannulene-capped nanotubes. [4]Circulene is at present an unknown aromatic compound.

Paired up! PGSE diffusion and ¹⁹F, ¹H HOESY NMR studies for a series of PF₆ salts in dichloromethane are presented. The extent of the ion pairing and the relative positions of the ions are shown to depend on the structure of the salt (an example is shown here). These new results show that the charge distribution and the ability of the anion to approach the positively charged positions (steric effects due to molecular shape) are the determining factors in deciding the amount of ion pairing.

A new route: Reactions of aryl boronic acid and allylic halides in the presence of a catalytic amount of a ruthenium complex do not provide the expected aryl addition, but lead to a new way for the synthesis of secondary allylic alcohols (see scheme).

An aldehyde group acts as a traceless control element when the Diels–Alder reaction with α,β-unsaturated aldehydes is combined with a rhodium-catalyzed decarbonylation in the same pot. In this way, acrolein, crotonaldehyde and cinnamaldehyde react as equivalents of ethylene, propylene, and styrene, respectively.

Selenium in a spin! The mechanisms and values of ⁿJ(Se,Se) (n=1–4) were analyzed by using the Gaussian 03 program and Slater-type functions at the DFT level. Our method explained the observed values and revealed torsional angular dependence in ¹J(Se,Se) and Fermi contact control in ⁴J(Se,Se). This helps us understand the electronic structure of diselenides and bis-selenides (see graphic).

Sweet hydrogels! A facile approach to a series of amphiphilic hydrogels has been devised from aminopolyols or sugar isocyanates. Water gelation can be achieved under thermal or mild sonochemical activation. Notably, some derivatives are also capable of forming lamellar and hexagonal mesogenic structures.

Fine-tuning of reactivity: Unprecedented tricyclic Δ¹-bipyrrolines, multiply substituted pyridines, siloles, and (Z,Z)-dienylsilanes were obtained in moderate to good yields by diverse reactions between 1,4-dilithio-1,3-dienes and nitriles (see scheme). These reactions were found to be strongly dependent on the substituents on the butadienyl skeleton and the nature of the nitriles employed.

Making the switch: A gated chiral molecular switch, with remote control of the photodimerization based on new binaphthalene molecules (S)-1 and (S)-2, was obtained by integration of the features of anthracene, binaphthalene, and 1,3-dithiole-2-thione/1,3-dithiole-2-one units (see scheme).