Fr Francium

Gold nanoparticles have been deposited on three kinds of carbon nanotubes (CNTs), including nitrogen-doped CNTs, by three different methods, namely, impregnation, organometallic decomposition, and deposition–precipitation. The choice of the gold precursor, the support, and the preparation procedure is critical for the control of the size and location (on or inside the nanotubes) of the gold nanoparticles. These catalysts were tested for the selective oxidation of CO in a hydrogen-rich atmosphere. We have shown that the use of nitrogen-doped CNTs as a support permits one to reach much higher activity and selectivity at low temperature than with the other CNT supports. This catalyst also shows a good stability under reaction conditions without detectable sintering.Gold nanoparticles have been selectively deposited on or inside different types of carbon nanotubes by using various synthetic strategies. The catalytic systems prepared on nitrogen-doped nanotubes show promising activity and selectivity for the selective oxidation of CO in a hydrogen-rich atmosphere.

Chelate ligands containing at least one pyrazole group were treated with RuCl2(PPh3)3, RuHCl(CO)(PPh3)3 and RuH2(CO)(PPh3)3 to form ruthenium complexes bearing protic N–H groups in close proximity to the catalytically active ruthenium centre. In the case of the hydridoruthenium complex RuHCl(CO)(PPh3)3 the resulting complexes also contain a basic hydrido ligand. The combination of acidic and basic hydrogen species in one molecule and the arising two-site reactivity was thoroughly investigated spectroscopically and by DFT calculations. Catalytic tests on the hydrogenation and transfer hydrogenation of acetophenone showed a general activity of these systems.Novel ruthenium complexes with protic N–H and hydridic Ru–H units can efficiently be obtained by combining hydridoruthenium precursors with pyrazole-derived ligands.

The design and synthesis of a new nanostructured material that can efficiently catalyze selective reduction reactions in an eco-friendly way is an active area of research today. Here a mesoporous Ni–Al mixed oxide material has been synthesized hydrothermally by using lauric acid as capping agent. The mesoporosity observed in the material is mainly originated from the interparticle voids created due to the self-assembly of the nanoparticles (NPs) in the presence of capping agent used during the synthesis. The material has been characterized by powder XRD, N2 sorption, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy/energy-dispersive spectroscopy (SEM-EDS), FTIR, and thermogravimetric/differential thermal analysis (TG-DTA) tools. The mesoporous Ni–Al mixed-oxide material showed a very high Brunauer–Emmett–Teller (BET) surface area (337 m2 g–1) and excellent catalytic activity in a selective liquid-phase hydride-transfer reduction reaction of nitroarenes to their corresponding anilines in the presence of 2-propanol as hydride source.Self-assembled mesoporous nickel–aluminum mixed oxide has been designed byusing lauric acid as the capping agent. The material showed excellent catalytic activity in selective liquid-phase hydride-transfer reduction.

We highlight the use of the robust [B(3,5-C6H3Cl2)4]– anion in organometallic chemistry. When partnered with organometallic cations, compared with [BArF4]– it presents desirable solubility properties, a lack of anion disorder in the solid-state, different coordinating properties with metal fragments and convenient metathetical routes for utilisation in synthesis.The use of the robust [B(3,5-C6H3Cl2)4]– anion in organometallic chemistry is described; this anion partnered with organometallic cations presents desirable solubility properties, a lack of anion disorder in the solid-state, different coordinating properties with metal fragments and convenient metathetical routes for utilisation in synthesis.

Historically, caged compounds have been used to interrogate the biological activity of organic molecules by using light; however, R. Tsien and others have developed methodologies over the last three decades for using nitrobenzyl-derived caged complexes to study the signaling behavior of Ca2+. A series of cation-selective N-phenyl-azamacrocyclic receptors integrated with a 4,5-dimethoxy-2-nitrobenzyl (DMNB) photoactive group act as cages for divalent metal ions. The uncaging mechanism of these complexes involves a photoreaction that converts the nitrobenzhydrol, which is para to the aniline nitrogen atom, into the corresponding nitrosobenzophenone. Resonance delocalization of the aniline into the distal carbonyl group of the photoproduct attenuates the ability of the nitrogen atom to interact with the guest. CrownCast-1 (3) utilizes a 13-phenyl-1,4,7,10-tetraoxa-13-azacyclopentadecane (A15C5, 2) receptor. Binding studies with CrownCast-1 revealed a modest selectivity for Ca2+; however, differences in the measured binding affinity uponphotolysis suggest that CrownCast-1 is better suited to cage Mg2+. CrownCast-2 (5) is derived from the Hg2+-selective10-phenyl-1,4-dioxa-7,13-dithia-10-azacyclopentadecane(AT215C5, 4) receptor. Aqueous binding studies demonstrate that CrownCast-2 binds tightly to Hg2+, but the strong sulfur–mercury interactions in the complex mitigate the release of the metal ion upon photolysis. Based on previous reports of metal selectivity, CrownCast-3 (7), which possesses a 16-phenyl-1,4,7,10,13-pentaoxa-16-azacyclooctadecane (A18C6, 6) receptor, was designed to act as a Pb2+ cage. Initial spectroscopic investigations suggest the uncaged ligand binds Pb2+ with higher affinity than the parent cage. To address this unexpected observation, a turn-on fluorescence sensor for Pb2+ that couples the A18C6 ligand with a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) fluorophore was synthesized. In contrast to the titration data, photolysis of [Pb(CrownCast-3)]2+ in the presence of PbSensor-1 (16) demonstrates that the uncaged ligand, CrownUnc-3 (15), binds Pb2+ with a lower affinity than the caged o-nitrobenzhydrol macrocycle.A series of macrocyclic ligands with pendant nitrobenzyl groups undergo photoreactions to yield benzophenone-based ligands with reduced binding affinity for metal ions. The cages can be used to controlmetal ion concentrations. In the macrocycle with two thioether groups, the ligand exhibits small changes in Hg2+ affinity since mercury is thiophilic.

Using the strategy of transition metal coordination together with that of large π-coordinating ligand complexation for planar tetracoordinate carbon (ptC) atoms, we present in this work a systematical DFT investigation on the possibility of ptC centers in M4C square sheets sandwiched in [CnHn]M4C[Cn′Hn′] complexes (M = Ni, Pd, Pt; n, n′ = 8, 9) with the planar π-coordinating ligands [C8H8]2– and [C9H9]–. Introduction of a ptC center into an M4 square sheet to form four effective ptC–M bonds helped to stabilize the [CnHn]M4C[Cn′Hn′] complexes thermodynamically, and the π-coordinating [C8H8]2– and [C9H9]– ligands were found to match the M4C middle decks both geometrically and electronically. Planar tetracoordinate boron (ptB) and nitrogen (ptN) behave similarly to ptC in these sandwich structures. These model sandwich complexes invite experimental syntheses and characterizations in order to open up a new area in coordination chemistry for planar tetracoordinate carbon and other non-metal atoms.The planar tetracoordinate carbon (ptC) centered [CnHn]M4C[Cn′Hn′] sandwich complexes with the large π-coordinating ligands [C8H8]2– and [C9H9]– invite experimental syntheses in order to open up a new area in coordination chemistry for planar tetracoordinate carbon and other non-metal atoms.

ortho-Metallated imines are commonly used as ligands for late transition metals. Unfortunately, not all metals, such as titanium, zirconium, and niobium, can undergo the necessary oxidative addition reactions to form the desired ortho-metallated complexes directly. Therefore, a synthetic methodology allowing easy access to this binding mode from simple early transition metal halides via an ortho-lithiated imine precursor is desirable. ortho-Lithiation of benzylamines and othersystems has been well studied; in contrast, that of imines is poorly developed. However, inclusion of a 3,4-methylenedioxy group on phenyl imines allows for straightforward lithiation and simple isolation of the ortho-lithiated imines. NMR spectroscopy and single-crystal X-ray diffraction allowed for the structural elucidation of the clustering in these lithium complexes. It has been determined that the nature of the imine nitrogen substituent has a profound effect on the clustering of the lithiated imines. Alkyl (Cy, tBu) substituents clustered in a tetrameric form, whereas aryl (2,6-R2C6H3; R = Me, Et, iPr) substituents formed dimers that exhibited long-range ordering in the solid state as coordination polymers. The introduction of coordinating solvent, such as dimethoxyethane and diethyl ether, changed the long-range order of the coordination polymer and in some cases, forced the formation of discrete dimeric lithium complexes. Lithium NMR spectroscopy indicates that in solution the coordination polymer breaks up to form discrete dimers. These complexes also display a pronounced decrease in the ring bond angle of the aromatic carbon atom directly attached to the lithium atom, which indicates an increase in the p-character of the carbon–lithium bond.Direct lithiation of phenyl imines has proven to be problematic; however, inclusion of a 3,4-methylenedioxy group on phenyl imines allows for the facile lithiation andisolation of ortho-lithiated imines. Single-crystal X-ray diffraction allowed the structural elucidation of the clustering in these lithium complexes in the solid state.

Two luminescent polypyridyl RuII complexes including dipyridin-2-ylamine (dpa) ligands functionalized by a maleimide group, namely [Ru(bpy)2(1a–b)](PF6)2 (bpy = 2,2′-bipyridyl; 1a = 1-[4-(dipyridin-2-ylamino)butyl]-1H-pyrrole-2,5-dione; 1b = 1-[5-(dipyridin-2-ylamino)pentyl]-1H-pyrrole-2,5-dione), were synthesized, and the X-ray structure of [Ru(bpy)2(1b)](PF6)2 was solved. The photophysical properties of these complexes and the starting dipyridin-2-ylamine ligands were studied. Upon excitation at their maximum of absorption, the dpa ligands exhibited weak luminescence because of quenching by the maleimide group. Conversely, the complexes displayed noticeable luminescence, with an emission wavelength at 600 nm that originated from a metal-to-ligand charge-transfer (MLCT) triplet state. Reaction of the ligands and the complexes with the cysteine endoproteinase papain was shown to occur at the single free cysteine (Cys25) as expected by the usual reactivity of maleimides. The resulting bioconjugates displayed luminescence assigned to the attached fluorophore, and luminescence enhancement was observed with respect to the starting reagents. The circular dichroism spectrum of one of the papain–RuII bioconjugates displayed a typical bisignate band in the near-UV range, indicating that the reaction of papain with the rac complex appeared to be stereoselective in favour of the Δ enantiomer.Reaction of dipyridin-2-ylamine complexes of RuII functionalized with a maleimide moiety with papain occurred in a stereoselective fashion and yielded bioconjugates displaying enhanced luminescence with respect to the starting materials.

Humana Press, Totowa 2010, XII+276 pp., hardcover $ 99.00.—ISBN 978-1-58829-950-5