Chemistry - A European Journal

Coherent photoisomerization is a rare, ultrafast process in which the photon energy activates a selected set of reactive vibrational modes, thus ensuring efficient photomechanical energy conversion. In their Full Paper on page 15296 ff., M. Olivucci, S. Haacke et al. combine experimental and theoretical approaches to investigate this process in a model molecular switch. Transient absorption reveals signatures of a quantum vibrational wave packet that drives the molecular motion from the electronic excited S1 to the ground S0 states, thus mimicking energy conversion in rhodopsin. Pronounced out-of-plane motions are predicted to modulate the π-orbital overlap across the twisted CC bond after decay to S0, and are held responsible for the observed oscillations.

One-dimensional ionic conduction paths are constructed by using self-assembled stacking of trilithium supramolecules. Because of the role allocation of lithium ions, one lithium ion holds the component units in specific positions to construct thermally stable channel structures with dynamic function and the others behave as carrier ions exhibiting selective lithium-ion conductivity. For more information see the Full Paper by M. Moriya, T. Yogo et al. on page 15305 ff.

The spin-crossover toolbox: A complete and concise overview of all the spin-crossover [Fe(Rtrz)₃][A]_x systems reported is provided (Rtrz is a 4-substituted-1,2,4-triazole; A=monovalent anion). The structural and magneto-optical properties of these one-dimensional coordination polymers are summarised, as well as their implementation into other phases of matter or nanostructured objects. The most relevant and recent developments based on this very attractive class of switchable materials are highlighted.

Dual-color imaging: Two-photon probes for lysosomes (BLT-blue) and mitochondria (FMT-green) that can be excited by 750 nm femtosecond laser pulses and emit at λ=400–450 and 550–600 nm, respectively, are reported. They allow simultaneous dual-color imaging of lysosomes and mitochondria in live cells and tissues for a long period of time with minimum interference from pH, photobleaching, or cytotoxicity (see scheme).

Seminaked extended metal-atom chains (EMACs) are suitable for the aerobic oxidation of CO to CO₂. One molecule of carbon dioxide remains attached to the metallic chain as a doubly deprotonated formate group (see figure), whereas the other is released. The reaction involves the activation and cleavage of a molecule of dioxygen with transfer of the atoms to two CO ligands.

The design and evaluation of fluorescence “turn-on” detection of melamine with cyanuric acid modified tetraphenylethene based on aggregation-induced emission, which can recognize the safe concentration level of melamine (1 ppm) in real powdered milk, is demonstrated (see figure).

Pincing CO₂: Group 10 (Pd, Pt) silyl pincer complexes in combination with B(C₆F₅)₃ can facilitate the efficient catalytic conversion of CO₂ to methane with a tertiary silane as the reductant under mild conditions. The reduction involves the formation of Pd and Pt formatoborate complexes.

Monomeric iminoalane: A donor-stabilized monomeric iminoalane was prepared by the reaction of 1 with an N-heterocyclic carbene (see scheme). The X-ray structure exhibits a very short AlN bond of 1.705(4) Å, which suggests multiple-bond character. Treatment of the iminoalane with phenyl acetylene, aniline, and carbon monoxide resulted in addition reactions to the formal AlN bond, thus indicating that the AlN multiple bond is highly reactive.

Triple bonds do it! The molybdenum-catalyzed CN bond cleavage of organic amides with hydrosilanes to produce alcohols and amines has been investigated. This work complements previously established protocols that lead to the cleavage of the CO bond. Modified triply bonded dimolybdenum(III) alkoxides have been found to be crucial for tuning the selectivity to CN bond cleavage (see figure).

Tiny flowers: A conceptually new method for fabricating polymer/Prussian blue (PB) hybrid flowers with ultrathin petals by using a CAICP technique has been developed. The PB hybrid flowers exhibit enhanced thermal stability, emit deep-blue light, and are electrochemically active. Their intriguing microstructure and enhanced structure-dependent properties make them potentially useful in nanodevices, biosensors, and photoluminescent devices.

Competition under control: A practical and efficient direct asymmetric vinylogous Michael reaction of deconjugated butenolides has been developed (see scheme). The products of this reaction, highly functionalized chiral succinimides, are obtained in excellent yield with high diastereoselectivity (up to d.r.=18:1) and outstanding enantioselectivity (up to e.r.=99.5:0.5).

Nanosheets rolling-up: The synthesis of MoO_3–x-based ultrathin nanosheets and their transformation into nanotubes, which is driven by the oxidation of Mo^V to Mo^VI, is reported. Tunable localized surface plasmon resonance can be achieved as the oxidation reaction proceeds gradually.

Spiro-spine! The effect of a spiro backbone was observed in the rhodium-catalyzed hydroformylation of terminal and internal olefins. High activity and excellent regioselectivity for the formation of linear aldehydes was realized in the case of the matched stereochemistry of the ligand (see scheme). It was found that the spiroketal is superior to biphenyl as the backbone of the ligand in terms of the regioselectivity of hydroformylation.

Coherent photoswitching: Wavepackets in both excited and ground states are identified as a remarkable property of the rhodopsin-mimicking indanylidene–pyrroline (IP) molecular switches. Simulations predict that pronounced out-of-plane motions triggered in the excited state modulate the π-orbital overlap across the twisted CC bond after decay to the ground state. The ensuing modulations in the S₀–S₁ transition energy are held responsible for the observed oscillations (see figure).

Formation of a conduction path: Ionic conduction paths were constructed by using self-assembled stacking of trilithium supramolecules with channel structures. Because of the role allocation of lithium ions, one lithium ion holds the component units in specific positions to construct thermally stable channel structures with dynamic function and the others behave as carrier ions exhibiting selective lithium-ion conductivity (see figure).

Hybrid materials: A new hybrid photonic antenna is presented, in which efficient Förster resonance energy transfer (FRET) occurs from a protected donor, entrapped into mesoporous SBA-15 platelets, to an acceptor dye, covalently bound on the silica surface (see figure). The FRET pair showed high photoluminescence and photostability, proving the material to be excellent for use as a light-harvesting system in optoelectronic applications (see figure).

Solvothermal synthesis: The formation of the three antimonato polyoxovanadates was studied with in situ X-ray diffraction. Nucleation and crystallization can be controlled by adjusting the amine concentration in a narrow concentration range and by using identical reactant ratios (see figure).

Sheeting the system: The chiral induction of α-amino acids was found to be significantly improved when attached to rigid layered double hydroxide nanosheets (see scheme), irrespective of whether they were applied as chiral ligands for Zn^II centers or as asymmetric catalysts alone in the direct aldol reaction.

Inherently chiral enolates: β-Lactams with contiguous tetra- and trisubstituted carbon centers were prepared in a highly enantioselective manner starting from α-amino acids through axially chiral enolates (see scheme; PMB=p-methoxybenzyl). The use of a weak base (metal carbonate) in a protic solvent (EtOH) is the key to smooth production of β-lactams.

In the frame: A ruthenium trichloride complex is loaded into an aluminium metal–organic framework by post-synthetic modification (see figure). This material is used in the heterogeneous catalysis of the oxidation of primary and secondary alcohols, including allylic alcohols, with PhI(OAc)₂ as the oxidant under mild reaction conditions. High selectivities for aldehydes are obtained at room temperature.

A relief map of the Laplacian of the electron density for the most stable H₂O@C₆₀ complex is illustrated. It shows the diffuse nature of the O atom, the electron-density pileup around the bonded carbon atoms, and the delocalized nature of the CC bonds in H₂O@C₆₀. Bond paths, connecting the nucleus of each atomic site of the guest with that of the atomic carbon atoms of the C₆₀ cage (dotted lines in atom color) indicate the presence of noncovalent interactions.

Broken symmetry: Unconventional triazine-based dendrimers (see figure) were prepared and, according to studies by differential scanning calorimetry, polarizing microscopy, and powder XRD, they display columnar liquid-crystalline (LC) phases. Simulations indicate that the conformations of the dendrimers are rather flat and disfavor formation of the LC phase. However, due to C₂-symmetry breaking, they have structural isomers in the solid state and thus show the desired columnar phases.

Photosensitized H₂generation by a series of Dye/TiO₂/Pt hybrids revealed clear dependence on the hydrophilic/hydrophobic character of the substituent R of Dye (see figure; Φ(H₂)=apparent quantum yield for H₂ generation.), which was shown by femtosecond transient spectroscopy to arise from the hydrophilic control of charge recombination (CR) between Dye^.+ and the injected electron TiO₂(e⁻).

Ratiometric probes for Cys/Hcy: Two new reagents have been developed as ratiometric and dual-channel chemodosimetric probes for the selective detection of cysteine and homocysteine under physiological conditions (see scheme). By virtue of their amphipathicity and insignificant cytotoxicity, these compounds could be used for in vivo imaging of intracellular Cys and Hcy in living HeLa cells. Furthermore, these reagents could also be used for the quantitative estimation of Cys in human blood plasma by using a modified pre-column HPLC technique.

Twist and radiate: The air- and moisture-stable 9,10-dianthryl-9,10-dihydro-9,10-diboraanthracenes (see figure) are reversible redox systems that show photoluminescence due to twisted intramolecular charge-transfer interactions, both in solution and in the solid state.

Growth changes: Crystal growth mechanisms of the metal–organic framework MOF-5 were studied by atomic force microscopy and observed to occur through a process of nucleation and spreading of metastable and stable sub-layers, revealing that MOFs may be considered as dense phase structures in terms of crystal growth. Crystal growth rates were found to depend on the framework metal ion/organic linker ratio (see figure).

Doubly doped: S/N-co-doped carbons were synthesised by facile annealing of nitrile-functionalised thiazolium salts. Materials with heteroatoms firmly incorporated into the carbon backbone were obtained (see figure; thia-DCA=3-methyl-thiazol-3-iumdicyanamide).

It's all about protection: Efficient shielding from dioxygen quenching has been observed for a new series of amphiphilic ruthenium–bathophenanthroline dendrimers (see figure). Photophysical studies revealed a positive dendritic effect, as evidenced by elongated excited-state lifetimes and increased emission quantum yields.

Radically antiferromagnetic: The slippage of benzotrazinyl radicals inside stacked columns inhibited dimerization and promoted orthogonality; however, the longer interplanar distances weakened the interaction. Magnetic studies revealed 1D antiferromagnetic interactions inside the columns (see figure).

Antitumor agents: Differential scanning calorimetry was used to determine the thermodynamic factors associated with the error-prone bypass that is catalyzed by the human DNA polymerase η of a bulky double-base lesion, which is induced in DNA by the antitumor platinum drug [PtCl₂(cis-1,4-dach)] (DACH=diaminocyclohexane; see scheme).

Pacman fever: A hetero-Pacman scaffold featuring a porphyrin and a terpyridine coordination pocket for metal-ion binding was produced by a modular strategy (see figure). A double Suzuki reaction gave a metalloligand with a free terpyridine coordination site. Subsequent reaction with iron triflate resulted in the isolation of a trinuclear compound.

Achieving stoichiometry: Stoichiometric and bulk CrN is formed through a solid-state ion-exchange reaction under high P–T conditions (see figure). Near-stoichiometric and well-crystallized CrN can also be synthesized at atmospheric pressure by the same procedure, implying the feasibility of industrial-scale production.

Long-lived charge separation! Photoexcitation of a ruthenium dye (RuP) on TiO₂ results in ultrafast electron injection into the semiconductor, and the resulting long-lived conduction-band electron has sufficient time to reach co-attached cobalt catalysts (CoP) for H₂ evolution in a pH-neutral solution and at room temperature (see figure).

In the year MM′X: The direct oxidation of heterobimetallic complexes allowed the expansion of so-called MMX 1D chains, which afforded the first mixed-metal mixed-valence MM′X system with dithiocarboxylate ligands (see picture).

In, with, or on water? There are many examples of Suzuki coupling reactions in pure water in the literature, but the biphasic nature of the mixture is widely unregarded (see figure). This work presents a study on the influence of significant parameters on the Suzuki coupling reaction by using different homogeneous Pd precatalysts.

Three is the key! Octahedral coordination of the Group 14 elements silicon, germanium, and tin is achieved with three chelating disulfate units (see figure) and results in complex [M(S₂O₇)₃]²⁻ ions, with the charge balances achieved by Ag⁺ and NH₄⁺. A comprehensive study of the compounds, including thermal, vibrational, NMR, and theoretical analysis, is presented.

Ring-producing expert: Ru complexes of redox-coupled cyclopentadienone ligands catalyze various allylation–cyclization reactions of cyclic 1,3-dicarbonyl compounds with 1-vinyl propargyl alcohols through strikingly distinct modes of activation to afford highly functionalized furans, pyrans, and spirocarbocycles (see scheme).

Directed interconversion: Three types of excited states (LE, ICT, and TICT) in the photochemical processes of a series of synthesized tridurylboranes are characterized by the conformation, the photophysical properties, and the thermodynamics of the intramolecular charge-transfer process. Effects of the solvent polarity, the viscosity, and the temperature on the fluorescence spectra reveal the interconversion and equilibria between the excited states (see figure).

A novel descriptor for non-covalent interactions, based on the reduced electron density gradient (RDG), enables easy visualisation of the zones of electron density ρ(r) involved in intermolecular interactions, for example, the CH⋅⋅⋅π interactions in the benzene crystal (see figure), whereas the quantum theory of atoms in molecules (QTAIM) bond path descriptor singles out two specific atom–atom links.

Tungsten in check: Various possible mechanisms of cleavage of the aromatic CC bond in quinoxaline by the W-based complex [W(PMe₃)₄(η²-CH₂PMe₂)H] were studied by using density functional theory calculations (see scheme). The results show that a recently proposed mechanism involves an overall barrier up to 42.0 kcal mol⁻¹ and does not seem to be consistent with experimental observations.

A pore show: Functionalized periodic mesoporous organosilicas (PMOs) with incorporated chiral Ni^II complexes exhibited high catalytic activity and enantioselectivity in the asymmetric Michael addition of 1,3-dicarbonyl compounds to nitroalkenes (see scheme; DACH=diaminocyclohexane).