| Carborane derivatives have been extensively studied in materials, microelectronics, optics, and medicines owing to their unique properties and potentials in applications. Among the already known polyhedral carboranes,1,2-dicarba-closo-dodecaborane (o-carborane) has been studied perticularly. The mononuclear16-electron half-sandwich complexes Cp#M(E2C2B10H10)(Cp#=Cp, Cp*; M=Co, Rh, Ir; E=S, Se) and (p-cymene)M(S2C2B10H10)(M=Ru, Os) possessing an o-carborane-1,2-dichalcogenolate ligand have been described extensively as a kind of attractive starting material:they could serve as precursors for the synthesis of multimetal clusters including heterometallic clusters with metal-metal bonds; they could react with Lewis bases such as NH3, CO, and N-heterocyclic ligands to construct their18-electron congeners; they could react with selected alkynes to generate novel compounds that result from insertion of alkynes into a M-E bond, followed by B-H activation, M-B bond formation and further chemical transformations. These sterically congested, coordinatively unsaturated compounds can be stored conveniently and used for the completion of various chemical transformations.Our group’s previous works showed that the reactivity of CpCo(S2C2B10H10)16e compounds was dependent on metal center, chalcogen element, ancillary ligand, substrate and even temperature, solvent as well as reactant ratio. However, the influence of substituted groups on boron atoms remained undiscovered and B3/B6disubstituted16e compound CpCo(S2C2B10H8)(CH=CH-C2Me)2(1S) was considered an final product without reactivity. However, recent work showed that1S had its own reactivity. This paper focuses on the reactivity of Boron substituted CpCo half-sandwich species, mainly1S, and the chemical nature of some products. The results are shown below:1. Reaction of16e Half-sandwich Complex CpCo(S2C2B10H8)(CH=CH-CO2Me)2(1S) in MethanolWhen stirred solely in MeOH,1underwent a self-convert and2was generated, intra molecular H-shift happened on one of the-CH=CH-CO2Me group, with the a-H shifted to the β-carbon to give a B-CH2unit, along with the formation of C(a)-Co bond. The reaction of1with ethynylferrocene (Fc-C=CH) and minor Dimethyl Acetylenedicarboxylate (DMAD, MeO2CC=CCO2Me) gave rise to3in which one equiv of MeO2CC=CCO2Me and Fc-C=CH inserted into one of the Co-S bond stereoselectively.2. Catalytic Activity of CpCo(S2C2B10H8)(CH=CH-CO2Me)2(1S) toward Cyclotrimerization of AlkynesFurther research showed that1S could serve as regioselective catalyst for2+2+2cycloadditions of alkynes in toluene when heated. A series of alkynes were selected to test the catalytic activity of1S. From the results we can find that1S was a mediate catalyst and its catalyst efficiency was determined mainly by temperature. Planar hindrance had negative influence on the efficiency of1S while steric hindrance would deprive the activity of1S.1S could be used at a low equiv (about4%) and was not sensitive to air and moisture, so there was no need for degas and dehydration of solvents.3. Ligand-to-Metal Ratio Controlled Assembly of16e Half-sandwich Complex CpCo(S2C2B10H8)(CH=CH-CO2Me)2(1S)Like16e compound CpCo(S2C2B10H10) could generate4S,1S reacted in THF at the presence of [N(n-Bu)4]Br and give [N(n-Bu)4][Co(S2C2B10H8)2(CH=CH-CO2Me)4]6S, in which the Cp unit and one equiv of Co were deprived and a Metal-dithiolene planar coordinate was formed. Similar structures(5S and7S) coming from different reactant were also synthesized. Due to the steric hindrance of substituents on boron sites,6S showed no activity towards alkynes. The electrochemical properties of4S-6S were tested using Cyclic Voltammetry Method and the results were discussed... |
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