Mechanistic insight into proton-coupled mixed valency

Stabilisation of the mixed-valence state in [Mo2(TiPB)3(HDOP)]2+ (HTiPB = 2,4,6-triisopropylbenzoic acid, H2DOP = 3,6-dihydroxypyridazine) by electron transfer (ET) is related to the proton coordinate of the bridging ligands. Spectroelectrochemical studies suggest that ET is slower than 109 s−1. The mechanism has been probed using DFT calculations, which show that proton transfer induces a larger dipole in the molecule resulting in ET

DDX3X suppresses the susceptibility of hindbrain lineages to medulloblastoma

DEAD-Box Helicase 3 X-Linked (DDX3X) is frequently mutated in the Wingless (WNT) and Sonic hedghog (SHH) subtypes of medulloblastoma—the commonest malignant childhood brain tumor, but whether DDX3X functions as a medulloblastoma oncogene or tumor suppressor gene is not known. Here, we show that Ddx3x regulates hindbrain patterning and development by controlling Hox gene expression and cell stress signaling. In mice predisposed to Wnt- or Shh medulloblastoma, Ddx3x sensed oncogenic stress and suppressed tumor formation. WNT and SHH medulloblastomas normally arise only in the lower and upper rhombic lips, respectively. Deletion of Ddx3x removed this lineage restriction, enabling both medulloblastoma subtypes to arise in either germinal zone. Thus, DDX3X is a medulloblastoma tumor suppressor that regulates hindbrain development and restricts the competence of cell lineages to form medulloblastoma subtypes

Structural, spectroscopic and theoretical studies of a diruthenium(II,II) tetraformamidinate that reversibly binds dioxygen

The reaction of Ru2(O2CMe)4 with N,N'-bis(3,5-dimethoxyphenyl)formamidine (Hdmof) in refluxing toluene solutions yields Ru2(dmof)4 as a diamagnetic red solid that is extremely airsensitive. The crystal structure reveals the expected paddlewheel arrangement of ligands around the Ru2 4+ core, with a relatively long Ru-Ru bond (2.4999(8) Å) that is consistent with a σ2 π4 δ2 π*4 electronic configuration. This is supported DFT calculations that show this electronic structure results from destabilization of the δ* orbital due to antibonding interactions with the formamidinate ligands. The cyclic voltammogram of Ru2(dmof)4 in a 0.1 M n Bu4NPF6 / CH2Cl2 solution shows two redox processes, assigned as successive oxidations corresponding to the Ru2 4+/5+ and Ru2 5+/6 redox couples. Changes in the electronic absorption spectra associated with these oxidation processes were probed using a UV/vis spectroelectrochemical study. Ru2(dmof)4 reacts with dioxygen in solution to generate a purple compound that decomposes within an hour at room temperature. Bubbling N2 gas through the purple solution regenerates Ru2(dmof)4, as evidenced by UV/vis spectrometry and cyclic voltammetry, suggesting that the dioxygen reversibly binds to the diruthenium core

Relationship between metal–metal bond length and internal rotation in diruthenium tetracarboxylate paddlewheel complexes

The Ru–Ru bond length for Ru2II,III and Ru2II,II paddlewheel complexes containing the bulky carboxylate ligand 2,4,6-triisopropylbenzoate was found to decrease despite a reduction in Ru–Ru bond order, due to increased internal rotation

Recent advances in the chemistry of metal-metal quadruple bonds

Metal–metal quadruple bonds can be formed between d4 metal ions, and tend to adopt one of two geometries; square parallelpiped or paddlewheel. In this chapter we outline recent efforts in the synthesis and characterization of quadruply bonded complexes of Cr(ii), Mo(ii), W(ii), Te(iii) and Re(iii). The quadruple bond is redox active and has a unique electronic structure, which results in it having interesting reactivity and photophysical properties. Their successful application as strong reducing agents, and in the study of electron transfer processes in the ground and photoexcited states, will be discussed

Recent developments in the chemistry of metal-metal multiply bonded paddlewheel compounds

This review summarises the main developments in the chemistry of metal-metal multiply bonded paddlewheel compounds reported in the literature between 2007 and 2008

Photophysical properties of metal complexes

This review summarises developments in the photophysical properties of metal complexes and their polynuclear assemblies reported in the literature for 200

Synthesis and Characterisation of Diruthenium Paddlewheel Compounds Bearing 2,6-Di(p-tolyl)benzoate Ligands

The mixed carboxylate diruthenium complexes trans-[Ru 2 II,III (O2CCH3)2(O2CAr)2Cl] (I) and trans-[Ru 2 II,II (O2CCH3)2(O2CAr)2] (II) (O2CAr = 2,6-di(p-tolyl)benzoate) have been synthesised along with [Ru 2 II,III (O2CAr)4Cl] (III) and the homoleptic complex [Ru 2 II,II (O2CAr)4] (IV). The structures trans-[Ru2(O2CCH3)2(O2CAr)2Cl(thf)]·(thf) and [Ru2(O2CAr)4Cl(η 1-CH2Cl2)] were determined by X-ray crystallography, and display the expected paddlewheel arrangement of the carboxylate ligands around the diruthenium core. The structure of III is a rare example of a structurally characterised dichloromethane complex, highlighting the Lewis acidic nature of the diruthenium axial position. The bulky −O2CAr ligand protects the axial positions from intermolecular interactions in the absence of strong nucleophiles for III and IV, and the effect this has on the electronic structure of the diruthenium core in these complexes was investigated by cyclic voltammetry, electronic absorption spectroscopy and magnetic susceptibility studies

Oxalate bridged heteronuclear compounds containing MM quadruple bonds (M = Mo and W) and their radical cations

The heteronuclear MM quadruply bonded oxalate bridged compound [(t-BuCO2)3MoW]2(µ-C2O4) (I) has been prepared from the reaction between MoW(O2Ct-Bu)4 and oxalic acid and characterized by elemental analysis, 1H NMR and UV-vis spectroscopy, and electrochemical studies. Single electron oxidation of I by reaction with Ag+PF6– leads to the formation of the kinetically labile radical cation I+, which has been characterized by UV-vis, NIR, and EPR spectroscopy. The latter results are compared with the properties of their related homonuclear Mo4- and W4-oxalate bridged compounds and their respective radical cations. The spectroscopic features of the related radical cations [(t-BuCO2)6MoxWy(µ-C2O4)]+, where x = 1, 2, 3 and y = 4 – x, are also described with the conclusion that the [(t-BuCO2)3Mo2(µ-C2O4)W2(O2Ct-Bu)3]+ and [(t-BuCO2)3Mo2(µ-C2O4)MoW (O2Ct-Bu)3]+ cations are valence trapped on the Robin and Day scheme for the classification of mixed valence compounds.Key words: molybdenum, tungsten, mixed valence