Synthesis and coordinating ability of an anionic cobaltabisdicarbollide ligand geometrically analogous to BINAP

The anionic chelating ligand [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]- has been synthesized from [3,3'-Co(1,2-C2B9H11)2]- in very good yield in a one-pot process with an easy work-up procedure. The coordinating ability of this ligand has been studied with Group 11 metal ions (Ag, Au) and with transition-metal ions (Pd, Rh). The two dicarbollide halves of the [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]- ligand can swing about one axis in a manner analogous to the constituent parts of BINAP and ferrocenyl phosphine derivatives. All these ligands function as hinges, with the most important property in relation to the coordination requirements of the metal being the PP distance. [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]-, BINAP, ferrocenyl phosphine derivatives, and other hinge ligands present a range of different PP separations, and consequently different coordination spheres and dispositions around metal cations. To account for these differences, the equation Dphi2 = D02 + 4 R2cos2(90-phi/2) has been developed. It relates the PP distance (Dphi) in a complex with the minimum PP distance (D0) that is characteristic of the hinge-type ligand.     

Electrochemistry of Cobalta Bis(dicarbollide) Ions Substituted at Carbon Atoms with Hydrophilic Alkylhydroxy and Carboxy Groups

In this study we explore the effect on the electrochemical signals in aqueous buffers of the presence of hydrophilic alkylhydroxy and carboxy groups on the carbon atoms of cobalta bis(dicarbollide) ions. The oxygen-containing exo-skeletal substituents of cobalta bis(dicarbollide) ions belong to the perspective building blocks that are considered for bioconjugation. Carbon substitution provides wider versatility and applicability in terms of the flexibility of possible chemical pathways. However, until recently, the electrochemistry of compounds substituted only on boron atoms could be studied, due to the unavailability of carbon-substituted congeners. In the present study, electrochemistry in aqueous phosphate buffers is considered along with the dependence of electrochemical response on pH and concentration. The compounds used show electrochemical signals around −1.3 and +1.1 V of similar or slightly higher intensities than in the parent cobalta bis(dicarbollide) ion. The signals at positive electrochemical potential correspond to irreversible oxidation of the boron cage (the C2B9 building block) and at negative potential correspond to the reversible redox process of (CoIII/CoII) at the central atom. Although the first signal is typically sharp and its potential can be altered by a number of substituents, the second signal is complex and is composed of three overlapping peaks. This signal shows sigmoidal character at higher concentrations and may be used as a diagnostic tool for aggregation in solution. Surprisingly enough, the observed effects of the site of substitution (boron or carbon) and between individual groups on the electrochemical response were insignificant. Therefore, the substitutions would preserve promising properties of the parent cage for redox labelling, but would not allow for the further tuning of signal position in the electrochemical window.     

13顶点金属碳硼烷结构和非线性光学性质的DFT研究

采用量子化学密度泛函理论(DFT)B3LYP/6-31G(d)方法,对4,1,6-MC2B10H1213顶点金属碳硼烷几何构型进行优化,结合有限场(FF)方法计算了它们的极化率和二阶非线性光学(NLO)系数.结果表明,十个13顶点金属碳硼烷分子中1a～6a的二阶NLO系数与其构型纵向扩张呈现相同的规律.分子的前线分子轨道能级差越小,其二阶NLO系数越大.对于不同自旋态的同种金属碳硼烷分子,其偶极矩值为高自旋态大于相应的低自旋态,极化率和二阶NLO系数与自旋多重度没有一致的对应规律,自旋多重度对NLO性质影响不大.     

Reversibly Switchable Fluorescent Molecular Systems Based on Metallacarborane–Perylenediimide Conjugates

Icosahedral metallacarboranes are θ-shaped anionic molecules in which two icosahedra share one vertex that is a metal center. The most remarkable of these compounds is the anionic cobalt-based metallacarborane [Co(C₂B₉H₁₁)₂]⁻, whose oxidation-reduction processes occur via an outer sphere electron process. This, along with its low density negative charge, makes [Co(C₂B₉H₁₁)₂]⁻ very appealing to participate in electron-transfer processes. In this work, [Co(C₂B₉H₁₁)₂]⁻ is tethered to a perylenediimide dye to produce the first examples of switchable luminescent molecules and materials based on metallacarboranes. In particular, the electronic communication of [Co(C₂B₉H₁₁)₂]⁻ with the appended chromophore unit in these compounds can be regulated upon application of redox stimuli, which allows the reversible modulation of the emitted fluorescence. As such, they behave as electrochemically-controlled fluorescent molecular switches in solution, which surpass the performance of previous systems based on conjugates of perylendiimides with ferrocene. Remarkably, they can form gels by treatment with appropriate mixtures of organic solvents, which result from the self-assembly of the cobaltabisdicarbollide-perylendiimide conjugates into 1D nanostructures. The interplay between dye π-stacking and metallacarborane electronic and steric interactions ultimately governs the supramolecular arrangement in these materials, which for one of the compounds prepared allows preserving the luminescent behavior in the gel state.     

Substituents effect on molecular structures of 13-vertex closo-metallacarboranes of rare earths. Synthesis and structural characterization of metallacarboranes bearing nido- and arachno-carborane ligands

Several new 13-vertex closo-metallacarboranes of rare earths incorporating nido- and arachno-carborane ligands have been prepared and structurally characterized. They represent a new class of metallacarboranes bearing a η⁷-carboranyl ligand recently discovered in our laboratory. This work indicates that the substituents on carborane cage carbons may affect the overall molecular structures of the resultant 13-vertex closo-metallacarborane complexes, but have little influence on the interactions between the central metal ion and nido- or arachno-carborane ligand.     

Syntheses and catalytic activities of Group 4 metal complexes derived from C(cage)-appended cyclohexyloxocarborane trianion

The reaction of Li[closo-1-Me-1,2-C₂B₁₀H₁₀] with cyclohexene oxide produced closo-1-Me-2-(2′-hydroxycyclohexyl)-1,2-C₂B₁₀H₁₀ (1) in 86% yield. Decapitation of (1) with potassium hydroxide in refluxing ethanol gave the corresponding cage-opened potassium salt of the carborane anion, [nido-1-Me-2-(2′-hydroxycyclohexyl)-1,2-C₂B₉H₁₀]⁻ (2) in 82% yield. Deprotonation of (2) with two equivalents of n-butyllithium in THF at −78 °C, followed by its further reaction with anhydrous MCl₄ · 2THF (M = Ti, Zr) produced the corresponding d⁰-half-sandwich metallacarboranes, closo-1-M(Cl)-2-Me-3-(2′-σ-O-cyclohexyl)-η⁵-2,3-C₂B₉H₉ (3 M = Zr; 4 M = Ti), in 59% and 51% yields, respectively. Reaction of Li[closo-1,2-C₂B₁₀H₁₁] with Merrifield’s peptide resin (1%) in refluxing THF gave the ortho-carborane-functionalized polymer (5) in 88% yield. The corresponding closo-1-polystyryl-2-(2′-hydroxycyclohexyl)-1,2-C₂B₁₀H₁₀ (6) was produced in 94% yield by refluxing a mixture of the lithium salt of (5) and cyclohexene oxide in THF for 2 days. Compound (6) was decapitated, deprotonated and then reacted with ZrCl₄ · 2THF to produce a polymer-supported d⁰-half-sandwich metallacarborane closo-1-Zr(Cl)-2-polystyryl-3-(2′-σ-O-cyclohexyl)-η⁵-2,3-C₂B₉H₉ (7) in 41% yield. Compounds (3) and (7), in the presence of MMAO-7 (13% ISOPAR-E), were found to catalyze the polymerization of ethylene and vinyl chloride in toluene to give high molecular weight PE (9.4 × 10³ (M_w/M_n = 1.8)) and PVC (2.1 × 10³ (M_w/M_n = 1.6)), respectively.