Periodic Mesoporous Organosilica Nanomaterials with Unconventional Structures and Properties.

Periodic mesoporous organosilicas (PMOs) are high surface area organic-inorganic hybrid nanomaterials that have found broad applications in various fields of research such as in (bio)chemistry or material science. By choosing suitable organic groups in the framework of these materials, their surface properties such as polarity, optical/electrical characteristics and adsorption capacity can be tuned. This critical review provides an overview of the current state of the art in the developments and applications of some PMO nanomaterials in diverse fields of research.

Task-Specific Janus Materials in Heterogeneous Catalysis.

Janus materials are anisotropic nano- and microarchitectures with two different faces consisting of distinguishable or opposite physicochemical properties. In parallel with the discovery of new methods for the fabrication of these materials, decisive progress has been made in their application, for example, in biological science, catalysis, pharmaceuticals, and, more recently, in battery technology. This Minireview systematically covers recent and significant achievements in the application of task-specific Janus nanomaterials as heterogeneous catalysts in various types of chemical reactions, including reduction, oxidative desulfurization and dye degradation, asymmetric catalysis, biomass transformation, cascade reactions, oxidation, transition-metal-catalyzed cross-coupling reactions, electro- and photocatalytic reactions, as well as gas-phase reactions.

Janus bifunctional periodic mesoporous organosilica.

Synthesis of a Janus periodic mesoporous organosilica material (JPMO) is presented here. In this strategy, the surface of the hollow silica material was selectively functionalized with two different bridged organic-inorganic hybrid groups. It was found that the resulting bifunctional material is able to form a stable Pickering emulsion.

Fast and Selective Aqueous-Phase Oxidation of Styrene to Acetophenone Using a Mesoporous Janus-Type Palladium Catalyst.

A heterogeneous Janus-type palladium interphase catalyst was obtained by selective surface modification of a hollow mesoporous silica material. The catalyst comprises hydrophobic octyl groups on one side of the silica nanosheets and single-site bis-imidazoline dichlorido palladium(II) complexes on the other. The structure of this composite material has been analyzed by means of elemental analysis, atomic absorption spectroscopy, BET surface analysis, TGA, SEM and solid-state CP-MAS C and Si NMR spectroscopy.

A Cyclometalated NHC Iridium Complex Bearing a Cationic (η -Cyclopentadienyl)(η -phenyl)iron Backbone*.

Nucleophilic substitution of [(η -cyclopentadienyl)(η -chlorobenzene)iron(II)] hexafluorophosphate with sodium imidazolate resulted in the formation of [(η -cyclopentadienyl)(η -phenyl)iron(II)]imidazole hexafluorophosphate. The corresponding dicationic imidazolium salt, which was obtained by treating this imidazole precursor with methyl iodide, underwent cyclometallation with bis[dichlorido(η -1,2,3,4,5-pentamethylcyclopentadienyl]iridium(III) in the presence of triethyl amine. The resulting bimetallic iridium(III) complex is the first example of an NHC complex bearing a cationic and cyclometallated [(η -cyclopentadienyl)(η -phenyl)iron(II)] substituent.

Dinuclear Copper Complex Immobilized on a Janus-Type Material as an Interfacial Heterogeneous Catalyst for Green Synthesis.

We herein describe a rational design of a heterogeneous catalyst composed of a dinuclear cuprate anion being immobilized electrostatically on one surface of Janus-type nanosheets while the other surface is decorated with highly hydrophobic octyl groups. The catalyst was found to be well dispersible in the organic phase of a biphasic aqueous/organic mixture. It was characterized by means of elemental analysis, atomic absorption spectroscopy, mass spectrometry, N absorption-desorption analysis, thermogravimetric analysis, scanning electron microscopy (SEM), and solid-state C and Si cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy.

Triazolyl Conjugated (Oligo)Phenothiazines Building Blocks for Hybrid Materials-Synthesis and Electronic Properties.

The Cu-catalyzed alkyne-azide 1,3-dipolar cycloaddition variant provides a highly efficient entry to conjugated triazolyl-substituted (oligo)phenothiazine organosilicon derivatives with luminescence and reversible redox characteristics. Furthermore, by in-situ co-condensation synthesis several representative mesoporous MCM-41 type silica hybrid materials with embedded (oligo)phenothiazines are prepared and characterized with respect to their structural and electronic properties. The hybrid materials also can be oxidized to covalently bound embedded radical cations, which are identified by their UV/Vis absorption signature and EPR signals.

Quantification of Cooperativity between Metal Sites in Dinuclear Transition Metal Complexes Containing the (2-Dimethylamino)-4-(2-pyrimidinyl)pyrimidine Ligand.

A concept for the quantification of cooperative effects in transition-metal complexes is presented. It is demonstrated for a series of novel N,N- (mononuclear) and C,N-coordinated homo- and heterometallic binuclear complexes based on the (2-dimethylamino)-4-(2-pyrimidinyl)pyrimidine ligand, which are accessible by applying roll-over cyclometallation. These iridium-, platinum-, and palladium-containing compounds are investigated with respect to their absorption and fluorescence spectra.

Photoinitiated Charge Transfer in a Triangular Silver(I) Hydride Complex and Its Oxophilicity.

The photoexcitation of a triangular silver(I) hydride complex, [Ag (μ -H)(μ -dcpm) ](PF ) ([P](PF ) , dcpm=bis(dicyclohexylphosphino)methane), designed with "UV-silent" bis-phosphine ligands, provokes hydride-to-Ag single and double electron transfer. The nature of the electronic transitions has been authenticated by absorption and photodissociation spectroscopy in parallel with high-level quantum-chemical computations utilizing the GW method and Bethe-Salpeter equation (GW-BSE). Specific photofragments of mass-selected [P] ions testify to charge transfer and competing pathways resulting from the unique [Ag (μ -H)] scaffold.

[2.2]Paracyclophanes with N-Heterocycles as Ligands for Mono- and Dinuclear Ruthenium(II) Complexes.

[2.2]Paracyclophane, with its unique structure, allows the design of unusual 3D structures by functionalization of this rigid and stable hydrocarbon scaffold. Therefore different mono- and homodisubstituted [2.

Cyclopalladation in the Periphery of a NHC Ligand as the Crucial Step in the Synthesis of Highly Active Suzuki-Miyaura Cross-Coupling Catalysts.

Starting from 2,4-dichloropyrimidine, 4-(2-dialkylamino)pyrimidinyl functionalized mesitylimidazolium chlorides are accessible in a five-step reaction sequence. Two routes leading to palladium NHC complexes derived from these ligands have been worked out: By transmetalation with the corresponding NHC-AgCl complexes, C,N-coordinated palladium(II) complexes can be obtained. Treatment of palladium dichloride with the imidazolium salts in pyridine and in the presence of K CO gives cyclometalated and thus C,C-coordinated compounds.

Exploring the Gas-Phase Activation and Reactivity of a Ruthenium Transfer Hydrogenation Catalyst by Experiment and Theory in Concert.

This study elucidates structures, activation barriers, and the gas-phase reactivity of cationic ruthenium transfer hydrogenation catalysts of the structural type [(η-cym)RuX(pympyr)]. In these complexes, the central ruthenium(+II) ion is coordinated to an η-bound p-cymene (η-cym), a bidentate 2-R-4-(2-pyridinyl)pyrimidine ligand (pympyr) with R = NH or N(CH), and an anion X = I, Br, Cl, or CFSO. We present infrared multiple-photon dissociation (IR-MPD) spectra of precursors (before HCl loss) and of activated complexes (after HCl loss), which elucidates C-H activation as the key step in the activation mechanism.

Mechanistic Studies on Ruthenium(II)-Catalyzed Base-Free Transfer Hydrogenation Triggered by Roll-Over Cyclometalation.

The synthesis of 2-substituted pyridine-pyrimidine ligands and their complexation with arene ruthenium(II) chloride moieties is reported. Depending on the electronic and steric influences of the ligand, the catalysts undergo CH activation by roll-over cyclometalation. This process opens up the route to the catalytic transfer hydrogenation of ketones with isopropanol as the hydrogen source under base-free and mild conditions.

Intermetallic Competition in the Fragmentation of Trimetallic Au-Zn-Alkali Complexes.

Cationization is a valuable tool to enable mass spectrometric studies on neutral transition-metal complexes (e.g., homogenous catalysts).

Multistate-Mediated Rearrangements and FeCl2 Elimination in Dinuclear FePd Complexes.

Mass spectrometric, spectroscopic, and computational characterization of a novel bifunctional iron-palladium complex proves a change of coordination upon solvation. Collisional excitation reveals FeCl2 and HCl elimination in a solvent-modulated competition. Hereby, syn and anti isomers, identified by theoretical calculations, favor and disfavor FeCl2 elimination, respectively.

Photoemission Studies on N-Substituted Dithienylated Phenothiazines.

Dithienylated phenothiazines (DTPTs) with different functional groups attached to the central nitrogen atom are presented as a class of versatile metal-free chromophores for the design of dye-sensitized solar cells (DSSCs) and organic light-emitting diodes (OLEDs). The electronic characteristics of spin-coated thin films on polycrystalline gold were studied using photoelectron spectroscopy assisted by theoretical calculations, scanning force microscopy, and UV/Vis spectroscopy. Complementary fluorescence spectra show light emission in the blue region (465 nm).

P,C-bond cleavage in the ligand sphere of a nickel(II) complex.

Reacting nickel(ii)perchlorate with a bidentate P,N-ligand in methanol leads to P,C-bond cleavage and gives a five-coordinate nickel complex wherein the nickel(ii) site is coordinated by a tridentate P,N,P-ligand and a bidentate N,C-ligand. The carbanion of the latter is the result of the P,C-bond cleaving process. The diamagnetic nickel(ii) complex was characterized by means of elemental analysis, NMR spectroscopy, cyclic voltammetry and X-ray structure analysis.

A rechargeable hydrogen battery based on Ru catalysis.

Apart from energy generation, the storage and liberation of energy are among the major problems in establishing a sustainable energy supply chain. Herein we report the development of a rechargeable H2 battery which is based on the principle of the Ru-catalyzed hydrogenation of CO2 to formic acid (charging process) and the Ru-catalyzed decomposition of formic acid to CO2 and H2 (discharging process). Both processes are driven by the same catalyst at elevated temperature either under pressure (charging process) or pressure-free conditions (discharging process).

Gold(I) complexes with heteroaryl phosphine ligands.

Gold(I) complexes ligated by phosphines with N-heterocycles in the periphery were prepared. First the synthesis of the ligands N-(diphenylphosphino)-4-(pyridin-2-yl)pyrimidin-2-amine (Hpypya) and N-(diphenylphosphino)-4-phenylpyrimidin-2-amine (Hphpya) are reported. These two compounds together with the related but earlier published ligands 3-(2-(diphenylphosphino)phenyl)-1H-pyrazole (Hph3py) and 5-(4-(diphenylphosphino)phenyl)-1H-pyrazole (Hph5py) were reacted with [(tht)AuCl] and [Au(tht)2]ClO4 to give the heteroleptic complexes [(L)AuCl] and the homoleptic compounds [(L)2Au]ClO4 (L = Hpypya, Hphpya, Hph3py, and Hph5py).

Evidence for the formation of a metal alkyl intermediate in the zinc mediated intramolecular hydroamination.

A diketiminato zinc amide complex, LZnNMe2 (1) [L = CH{(CMe)2(2,6-(i)Pr2C6H3N)2}], was prepared and investigated for the catalytic hydroamination of 2,2-dimethylpent-4-en-1-amine. The reaction with the amino olefin resulted in a transamination reaction and the subsequent insertion of the olefin moiety into the metal-amide bond. However, the reaction stopped at this point providing access to the metal alkyl intermediate, LZnR (R = N[upper bond 1 start]H-CH2-CPh2-CH2-C[upper bond 1 end]H-) (2).

Chemisorption of exchange-coupled [Ni2L(dppba)]+ complexes on gold by using ambidentate 4-(diphenylphosphino)benzoate co-ligands.

A new strategy for the fixation of redox-active dinickel(II) complexes with high-spin ground states to gold surfaces was developed. The dinickel(II) complex [Ni2L(Cl)]ClO4 (1ClO4), in which L(2-) represents a 24-membered macrocyclic hexaaza-dithiophenolate ligand, reacts with ambidentate 4-(diphenylphosphino)benzoate (dppba) to form the carboxylato-bridged complex [Ni2L(dppba)](+), which can be isolated as an air-stable perchlorate [Ni2L(dppba)]ClO4 (2ClO4) or tetraphenylborate [Ni2L(dppba)]BPh4 (2BPh4) salt. The auration of 2ClO4 was probed on a molecular level, by reaction with AuCl, which leads to the monoaurated Ni(II)2Au(I) complex [Ni(II)2L(dppba)Au(I)Cl]ClO4 (3ClO4).

Structure-reactivity relationships in the hydrogenation of carbon dioxide with ruthenium complexes bearing pyridinylazolato ligands.

Pyridinylazolato (N-N') ruthenium(II) complexes of the type [(N-N')RuCl(PMe3)3] have been obtained in high yields by treating the corresponding functionalised azolylpyridines with [RuCl2 (PMe3)4] in the presence of a base. (15)N NMR spectroscopy was used to elucidate the electronic influence of the substituents attached to the azolyl ring. The findings are in agreement with slight differences in the bond lengths of the ruthenium complexes.

Efficient conversion of arylene precursors into photoluminescent phosphonates for surface modification of metal oxides.

Three highly fluorescent phosphonates have been prepared in good yields from different arylene bridged 5-iodothiophenes by following an optimized four-step procedure. The compounds have been immobilised on mesoporous zirconia, alumina and titania particles in order to probe their luminescence properties on the surfaces. The organic compounds as well as the obtained hybrid materials have been characterised using liquid phase or MAS NMR spectroscopy, N2 physisorption measurements, ATR-IR spectroscopy and elemental analysis.

Three modes of proton transfer in one chromophore: photoinduced tautomerization in 2-(1H-pyrazol-5-yl)pyridines, their dimers and alcohol complexes.

Studies of 2-(1H-pyrazol-5-yl)pyridine (PPP) and its derivatives 2-(4-methyl-1H-pyrazol-5-yl)pyridine (MPP) and 2-(3-bromo-1H-pyrazol-5-yl)pyridine (BPP) by stationary and time-resolved UV/Vis spectroscopic methods, and quantum chemical computations show that this class of compounds provides a rare example of molecules that exhibit three types of photoreactions: 1) excited-state intramolecular proton transfer (ESIPT) in the syn form of MPP, 2) excited-state intermolecular double-proton transfer (ESDPT) in the dimers of PPP in nonpolar media, as well as 3) solvent-assisted double-proton transfer in hydrogen-bonded 1:1 complexes of PPP and MPP with alcoholic partners. The excited-state processes are manifested by the appearance of a dual luminescence and a bimodal irreversible kinetic coupling of the two fluorescence bands. Ground-state syn-anti equilibria are detected and discussed.