Insights into the mechanism for gold catalysis: behaviour of gold(i) amide complexes in solution

We report the synthesis and activity of new mononuclear and dinuclear gold amide complexes . The dinuclear complexes and were characterised by single crystal X-ray analysis. We also report solution NMR and freezing point depression experiments to rationalise their behaviour in solution and question the de-ligation process invoked in gold catalysis

Conformational control of anticancer activity: the application of arene-linked dinuclear ruthenium(II) organometallics

Dinuclear metal complexes have emerged as a promising class of biologically active compounds which possess unique anticancer activity. Here, we describe a novel series of arene-linked dinuclear organometallic Ru(II) complexes, where the relative conformation of the ruthenium centres is controlled by the stereochemical configuration of 1,2-diphenylethylenediamine linker moieties, as confirmed by X-ray crystallography. The reactivity and cytotoxicity of these compounds is compared to flexible dinuclear and mononuclear analogues, demonstrating in all cases the complexes can undergo aquation, coordinate to typical biological donor ligands and importantly, in the case of dinuclear analogues, crosslink oligonucleotide and peptide sequences. Differences in the conformation of the isomeric dinuclear compounds lead to significantly different levels of cytotoxicity against A2780, A2780cisR and HEK-293 cell lines; isomers with a closed conformation are significantly more cytotoxic than isomers with a more open conformation and they are also significantly less susceptible to acquired resistance mechanisms operating in the A2780cisR cell line. These rigid dinuclear compounds possess markedly increased cytotoxicity relative to the non-cytotoxic mononuclear analogues that does not appear to be related to differences in complex lipophilicity or cellular uptake, which, in general, remain similar in magnitude across the series. Thus, the molecular conformation of such dinuclear species may be crucial in determining the nature of the adducts formed on coordination to biological targets in a cellular environment, and opens up a novel route toward the development of more active metal-based anticancer agents

Isolation of bis(copper) key intermediates in Cu-catalyzed azide-alkyne "click reaction".

The copper-catalyzed 1,3-dipolar cycloaddition of an azide to a terminal alkyne (CuAAC) is one of the most popular chemical transformations, with applications ranging from material to life sciences. However, despite many mechanistic studies, direct observation of key components of the catalytic cycle is still missing. Initially, mononuclear species were thought to be the active catalysts, but later on, dinuclear complexes came to the front. We report the isolation of both a previously postulated π,σ-bis(copper) acetylide and a hitherto never-mentioned bis(metallated) triazole complex. We also demonstrate that although mono- and bis-copper complexes promote the CuAAC reaction, the dinuclear species are involved in the kinetically favored pathway

Electron Capture Dissociation Mass Spectrometry of Metallo-Supramolecular Complexes

The electron capture dissociation (ECD) of metallo-supramolecular dinuclear triple-stranded helicate Fe2L3 4 ions was determined by Fourier transform ion cyclotron resonance mass spectrometry. Initial electron capture by the di-iron(II) triple helicate ions produces dinuclear double-stranded complexes analogous to those seen in solution with the monocationic metal centers CuI or AgI. The gas-phase fragmentation behavior [ECD, collision-induced dissociation (CID), and infrared multiphoton dissociation (IRMPD)] of the di-iron double-stranded complexes, (i.e., MS3 of the ECD product) was compared with the ECD, CID, and IRMPD of the CuI and AgI complexes generated from solution. The results suggest that iron-bound dimers may be of the formFeI 2L2 2 and that ECD by metallo-complexes allows access, in the gas phase,to oxidation states and coordination chemistry that cannot be accessed in solution

Synthesis, Characterization, and Properties of Mononuclear and Dinuclear Ruthenium(II) Complexes Containing Phenanthroline and Chlorophenanthroline

The study of photophysical and photochemical properties of ruthenium complexes is of great interest for fundamental practical reasons. Ruthenium complexes have been investigated for use in artificial photosynthesis. This paper deals with the synthesis and spectroscopic investigation of custom-designed ruthenium complexes containing phenanthroline and chloro-phenanthroline ligands. These complexes maybe useful for biological electron-transfer studies. The heteroleptic ruthenium monomer complex Ru(phen)2(Cl-phen) (where phen = 1,10-phenanthroline and Cl-phen=5-chloro-1,10-phenanthroline) was prepared in a two-step procedure previously developed in our laboratory. This monomer complex was used to prepare the ruthenium homometallic dimer complex, (phen)2Ru(phen-phen)Ru(phen)2, by utilizing the Ni-catalyzed coupling reaction. Both complexes were purified by extensive column chromatography. The identity and the integrity of the monomer complex were confirmed by elemental analysis. The calculated and the experimental values for the elemental analysis were in good agreement for the monomer complex. UV/Vis absorption spectroscopy, emission spectroscopy, and cyclic voltammetry were used to investigate the properties of both the complexes

An Oxalate-Bridged Copper(II) Complex Combining Monodentate Benzoate, 2,2'-bipyridine and Aqua Ligands:Synthesis, Crystal Structure and Investigation of Magnetic Properties

A dinuclear copper(II) complex of formula [{Cu(bipy)(bzt)(OH2)}2(μ-ox)] (1) (where bipy = 2,2'-bipyridine, bzt = benzoate and ox = oxalate) was synthesised and characterised by diffractometric (powder and single-crystal XRD) and thermogravimetric (TG/DTG) analyses, spectroscopic techniques (IR, Raman, electron paramagnetic resonance spectroscopy (EPR) and electronic spectroscopy), magnetic measurements and density functional theory (DFT) calculations. The analysis of the crystal structure revealed that the oxalate ligand is in bis(bidentate) coordination mode between two copper(II) centres. The other four positions of the coordination environment of the copper(II) ion are occupied by one water molecule, a bidentate bipy and a monodentate bzt ligand. An inversion centre located on the ox ligand generates the other half of the dinuclear complex. Intermolecular hydrogen bonds and π-π interactions are responsible for the organisation of the molecules in the solid state. Molar magnetic susceptibility and field dependence magnetisation studies evidenced a weak intramolecular-ferromagnetic interaction (J = +2.9 cm-1) between the metal ions. The sign and magnitude of the calculated J value by density functional theory (DFT) are in agreement with the experimental data

Mechanism of efficient anti-Markovnikov olefin hydroarylation catalyzed by homogeneous Ir(III) complexes

The mechanism of the hydroarylation reaction between unactivated olefins (ethylene, propylene, and styrene) and benzene catalyzed by [(R)Ir(μ-acac-O,O,C^3)-(acac-O,O)_2]_2 and [R-Ir(acac-O,O)_2(L)] (R = acetylacetonato, CH_3, CH_2CH_3, Ph, or CH_2CH_2Ph, and L = H_2O or pyridine) Ir(III) complexes was studied by experimental methods. The system is selective for generating the anti-Markovnikov product of linear alkylarenes (61 : 39 for benzene + propylene and 98 : 2 for benzene + styrene). The reaction mechanism was found to follow a rate law with first-order dependence on benzene and catalyst, but a non-linear dependence on olefin. ^(13)C-labelling studies with CH_3^(13)CH_2-Ir-Py showed that reversible β-hydride elimination is facile, but unproductive, giving exclusively saturated alkylarene products. The migration of the ^(13)C-label from the α to β-positions was found to be slower than the C–H activation of benzene (and thus formation of ethane and Ph-d_5-Ir-Py). Kinetic analysis under steady state conditions gave a ratio of the rate constants for CH activation and β-hydride elimination (k_(CH): k_β) of 0.5. The comparable magnitude of these rates suggests a common rate determining transition state/intermediate, which has been shown previously with B3LYP density functional theory (DFT) calculations. Overall, the mechanism of hydroarylation proceeds through a series of pre-equilibrium dissociative steps involving rupture of the dinuclear species or the loss of L from Ph-Ir-L to the solvento, 16-electron species, Ph-Ir(acac-O,O)_2-Sol (where Sol refers to coordinated solvent). This species then undergoes trans to cis isomerization of the acetylacetonato ligand to yield the pseudo octahedral species cis-Ph-Ir-Sol, which is followed by olefin insertion (the regioselective and rate determining step), and then activation of the C–H bond of an incoming benzene to generate the product and regenerate the catalyst

Synthesis and coordination chemistry of 2-(di-2-pyridylamino)pyrimidine; structural aspects of spin crossover in an Fe(II) complex

This paper was accepted on February 26 20122-(Di-2-pyridylamino)pyrimidine (L), a potentially ditopic tetradentate ligand, was synthesized from commercially available di-2-pyridylamine and 2-chloropyrimidine. Despite being capable of bridging two metal atoms with bidentate chelation of both metal centres, L prefers to chelate or bridge through the more basic pyridyl donors of the di-2-pyridylamine moiety. Mononuclear trans-[Fe(NCS)2(L)2] and [Cu(L)2(H2O)](BF4)2•H2O complexes, and a discrete [Ag2(L)4](PF6)2 metallomacrocycle were isolated and structurally characterized by X-ray crystallography. A mononuclear palladium complex [PdCl2(L)]•(solvate), where solvate = ½H2O or CH2Cl2, was also readily obtained in 71% yield. One example of the ligand acting as a bis(bidentate) bridging ligand was observed in a dinuclear [(PdCl2)2(L)]•¾H2O complex that was obtained only in very low yield (ca. 3%) from the reaction that produced [PdCl2(L)]•½H2O. trans-[Fe(NCS)2(L)2] undergoes a temperature dependent HS-LS (HS = high spin; LS = low spin) crossover at ca. 205 K that was 2 observed by X-ray crystallography and magnetic measurements and attempts were made to understand the structural basis of this process. Despite efforts to isolate examples of L bridging two iron(II) centres, only the mononuclear trans-[Fe(NCS)2(L)2] species could be obtained.Rachel S. Crees, Boujemma Moubaraki, Keith S. Murray, and Christopher J. Sumb

Highly selective and sensitive macrocycle-based dinuclear foldamer for fluorometric and colorimetric sensing of citrate in water.

The selective detection of citrate anions is essential for various biological functions in living systems. A quantitative assessment of citrate is required for the diagnosis of various diseases in the human body; however, it is extremely challenging to develop efficient fluorescence and color-detecting molecular probes for sensing citrate in water. Herein, we report a macrocycle-based dinuclear foldamer (1) assembled with eosin Y (EY) that has been studied for anion binding by fluorescence and colorimetric techniques in water at neutral pH. Results from the fluorescence titrations reveal that the 1·EY ensemble strongly binds citrate anions, showing remarkable selectivity over a wide range of inorganic and carboxylate anions. The addition of citrate anions to the 1·EY adduct led to a large fluorescence enhancement, displaying a detectable color change under both visible and UV light in water up to 2 μmol. The biocompatibility of 1·EY as an intracellular carrier in a biological system was evaluated on primary human foreskin fibroblast (HF) cells, showing an excellent cell viability. The strong binding properties of the ensemble allow it to be used as a highly sensitive, detective probe for biologically relevant citrate anions in various applications