Several biscarborane-type derivatives of 8-iodo-1,2-dicarba-closo-dodecaborane (1), suitable as the precursors of linear metallacarborane-based molecular rods, were prepared. The synthesized closo-compounds contained two carborane moieties connected through a rigid linear unsaturated linker. The linkers were based on ethynylene and para-phenylene fragments and their combinations. The deboronation of all reported closo-compounds was selective and afforded nido-products with open pentagonal faces on opposite sides of the molecule, parallel to each other and perpendicular to the main molecular axis. All of the closo and nido products were characterized by a variety of physical methods (NMR, HRMS, IR). The structures of closo-carboranes 3, 6, 9, and 14 and nido-carboranes 15 and 17 were established by X-ray diffraction.

Two approaches for the synthesis of rodlike polymers having metal bis(dicarbollide) anions connected by organic linkers, such as acetylene and 1,4-dibutyl-2,5diethynylbenzene, in the backbone are reported. Route 1 involved connecting nido-bis(carborane) compounds, containing the linkers, via π coordination with Co or Ni metals. This reaction yielded small oligomers having one to six repeating units. Route 2 utilized a palladium-catalyzed cross-coupling copolymerization of diiodo-substituted cobaltocarboranes and a zinc-derivatized aromatic linker. This approach gave a mixture of oligomers and polymers. The polymers were separated from the smaller oligomers by dialysis and were characterized by 1 H NMR, 11 B NMR, 11 B{ 1 H} NMR, IR, UV−vis, TEM, and AFM techniques. End-group analysis and dynamic-light scattering experiments (DLS) determined that the average number of repeating units in the polymers ranged between 35 and 44. GPC analyses failed to aid the molecular weight determination due to the adsorption of the polymers to the stationary phase of the column. Dilute-solution viscometry experiments supported the semirigid nature of these polymers.

Aromatized cationic [(PNN)Re(π acid)(O)2](+) (1) and dearomatized neutral [(PNN*)Re(π acid)(O)2] (2) complexes (where π acid=CO (a), tBuNC (b), or (2,6-Me2)PhNC (c)), possessing both π-donor and π-acceptor ligands, have been synthesized and fully characterized. Reaction of [(PNN)Re(O)2](+) (4) with lithiumhexamethyldisilazide (LiHMDS) yield the dearomatized [(PNN*)Re(O)2] (3). Complexes 1 and 2 are prepared from the reaction of 4 and 3, respectively, with CO or isocyanides. Single-crystal X-ray structures of 1 a and 1 b show the expected trans-dioxo structure, in which the oxo ligands occupy the axial positions and the π-acidic ligand occupies the equatorial plane in an overall octahedral geometry about the rhenium(V) center. DFT studies revealed the stability of complexes 1 and 2 arises from a π-backbonding interaction between the d(xy) orbital of rhenium, the π orbital of the oxo ligands, and the π* orbital of CO/isocyanide.

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The synthesis and characterization of ReI and ReII dicarbonyl halides 1 and 2 and the ReIII dicarbonyl dihalide 3 supported by a PNN pincer ligand are described. Complex 1 (1a, X = Br; 1b, X = Cl) was synthesized by refluxing the PNN ligand with Re(CO)5X (X = Br, Cl) in toluene. One-electron oxidation of 1 by [(4-BrC6H4)3N][SbCl6] gave 2, which when oxidized by PhIO afforded 3. X-ray and IR analysis of 1–3 revealed a systematic increase of Re–C(O) and decrease of CO bond lengths and increase in the corresponding CO stretching frequency. All of these results are consistent with weakening in the Re–C(O) bond from 1 to 3 upon increasing the oxidation state from +1 in 1 to +3 in 3, with 2 being in between. The heptacoordinate complex 3 exhibited temperature-dependent fluxional behavior, caused by the pseudorotation of the rhenium center. This phenomenon was observed by NMR and supported computationally by density functional theory (DFT) calculations.