Transition metal mediated functionalization of o-carboranes

<正>Carboranes are a class of boron hydride clusters in which one or more of the BH vertices are replaced by CH units.Unlike small boranes, carboranes are kinetically and thermodynamically very stable as well as relatively chemically inert, which are often called three-dimensional relatives of benzenes. They are finding many applications in medicine as boron neutron capture therapy(BNCT) agents, in nanomaterials/supramolecular design as building blocks, and as ligands for transition metals [1]. However, their unique structures make derivatization difficult, which limits their application scope. To this end, there is a need to develop     

碳硼烷和碳硼炔金属配合物中金属-碳键的化学性质

碳硼烷和碳硼炔金属配合物中的金属-碳键具有不同于经典金属-碳键的化学性质.一方面,二十面体碳硼烷独特的电子和空间效应使得碳硼烷金属配合物中的金属-碳键不参与和不饱和分子的反应 另一方面,在一定条件下具有大空间位阻的碳硼笼可以诱导某些碳-碳偶联反应.然而,碳硼炔金属配合物中的金属-碳键能与多种不饱和分子发生反应,其反应模式取决于中心金属离子的电子构型.本文简要总结了我们近期在这方面的研究进展.     

Synthesis of carborane-fused cyclobutenes and cyclobutanes

Transmetalation of carborane-fused zirconacycles to Cu(Ⅱ) induces the C-C coupling reaction to form four-membered rings. This serves as a new efficient and general methodology for the generation of a series of carborane-fused cyclobutenes and cyclobutanes. A reaction mechanism involving transmetalation to Cu(Ⅱ) and reductive elimination is proposed.     

A DFT study the solvent effects of H2 adsorption on Cu(h k l) surface

Density functional theory (DFT) combined with conductor-like solvent model (COSMO) have been performed to study the solvent effects of H₂ adsorption on Cu(h k l) surface. The result shows H₂ can not be parallel adsorbed on Cu(h k l) surface in gas phase and only vertical adsorbed. At this moment, the binding energies are small and H₂ orientation with respect to Cu(h k l) surfaces is not a determining parameter. In liquid paraffin, when H₂ adsorbs vertically on Cu(h k l) surface, solvent effects not only influences the adsorptive stability, but also improves the ability of H₂ activation; When H₂ vertical adsorption on Cu(h k l) surface at 1/4 and 1/2 coverage, H-H bond is broken by solvent effects. However, no stable structures at 3/4 and 1 ML coverage are found, indicating that it is impossible to get H₂ parallel adsorption on Cu(h k l) surfaces at 3/4 and 1 ML coverages due to the repulsion between adsorbed H₂ molecules.     

Influence of amplified spontaneous emission and fluorescence of β-carotene on stimulated Raman scattering of carbon disulfide

β-carotene with double fluorescence characteristics and large third-order optical nonlinearities, which is dissolved in the carbon disulfide (CS₂) as the core medium of a liquid core optical fiber (LCOF), is applied in the study of the CS₂ stimulated Raman scattering (SRS). The results of this study show that when the concentrations of solution are more than 3.72×10⁻⁷ mol/L, the amplified spontaneous emission (ASE) of β-carotene is the main factor influencing the threshold and intensity of Stokes lines; when the concentrations of solution are lower than 3.72×10⁻⁷ mol/L, the ASE disappears and the fluorescence plays the key role: The high-order Stokes lines may be observed at very low input-laser power, and the Stokes thresholds decrease as the solution concentration increases. The result may be widely used in the study of broadband stimulated radiation laser and seeding laser. Supported by the National Natural Science Foundation of China (Grant No. 10774057)     

Highly regio- and enantioselective synthesis of chiral polysubstituted 2H-pyrroles

<正>As one of the most important five-member heterocyclic aromatic rings, pyrrole is widely distributed in numerous natural products and pharmaceutical agents. Asymmetric dearomatization of pyrroles is very attractive in organic synthesis given the fact that highly functionalized chira pyrrolines and pyrrolidines could be easily accessed from the readily available pyrroles. However, the reported asymmetric dearomatization reactions of pyrroles are limited to transition-metal-catalyzed [4+3] cycloaddition and hydrogenation reactions. The enantioselective intermolecular alkylative dearomatization of pyrroles is rare and challenging due to multiple selectivity issues including the     

Reaction of [η 5:σ-Me2C(C5H4)(C2B10H10)]Ru(NCCH3)2 with internal alkynes: Synthesis and structural characterization of ruthenium-cyclobutadiene and ruthenacyclopentatriene complexes

Reaction of [η ⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(NCCH₃)₂ (1) with R¹C≡CR¹(R¹ = Et, Ph) in toluene at 80°C yielded organoruthenium cyclobutadiene complexes [η ⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(η ⁴-C₄R ₄ ¹ ) in >80% yield. Treatment of 1 with diynes R₂C≡C(CH₂)₃C≡CR² (R² = Me, Et) in toluene at room temperature yielded ruthenacyclopentatrienes [η ⁵:σ-Me₂C (C₅H₄)(C₂B₁₀H₁₀)]Ru[=C₂(R²)₂C₂(CH₂)₃] in >85% yield. These new complexes were fully characterized by various spectroscopic techniques, elemental analyses and single-crystal X-ray diffraction studies. The possible reaction mechanism was proposed.     

Role of Carborane in Polymerization and Insertion Reactions

Ligand modifications have played a crucial role in developing new catalyst precursors. A novel class of “constrained-geometry”ligands bearing a carboanion functionality has been developed by linking o-carboranyl and n-ligand together. They offer group 4 metal complexes higher activity in olefin polymerization compared to those with appeoded heteroatom systems. The results show that the [{η^5：σ-Me2A（C5H4）（C2B10H10）}M] moiety remains intact in olefin polymerization and insertion reactions of various unsaturated molecules, and the electron-deficient yet sterically hindered icosahedral carborane does play an important role in the reactions. This article provides an overview of our recent work on this subject.     

Unique chemical properties of metal-carbon bonds in metal-carboranyl and metal-carboryne complexes

The metal-carbon bonds in metal-carboranyl and metal-carboryne complexes behave very differently from those in classical organometallic complexes. The unique electronic and steric properties of ico-sahedral carboranyl moiety make the M-C bond in metal-carboranyl complexes inert toward unsaturated molecules, and on the other hand, the sterically demanding carborane cage can induce unexpected C-C coupling reactions. The M-C bonds in metal-carboryne complexes are, however, active toward various kinds of unsatu...