1Camouflaged Carborarods Derived from B-permethyl- 1,12-diethynyl-para-carborane Modules

Abstract: Rigid camouflaged carborarods constructed from the corresponding C,C'-diethynyl derivatives of B-decamethyl-1,12-dicarbadodecaborane(12) (6) have been synthesized via largely conventional organic transformations. These carborarods are the longest discrete rod species available by this method in which B-methylated p-carborane cages are linked through their carbon vertices using butadiynylene moieties. They exhibit enhanced solubility in common organic solvents relative to all other presently known carborane-based rigid rod molecules. The oxidative coupling of bis-(ethynyl) derivatives of 6 generates oligomers containing, on the average, 16 carborane modules. The structural characterization of the corresponding dimeric species revealed that the carborarods possess a sinusoidal distortion in the solid-state. The electronic properties of these and related model carborarods were evaluated by both computational and experimental methods. In addition, the effect of exhaustive B-methylation of 12- and 10-vertex carborane cages in a series of model C,C'-diethynyl derivatives was investigated by computational and structural studies. A correlation of C-C bond lengths with cage size was observed, while B-permethylation had no significant effect with either 10- or 12- vertex cage derivatives. Thermal and chemical stabilization was increased through the operation of a steric bumper-car process. The formation of linear sterically encumbered platina-carborarods using ethynyl derivatives of 6 as 2precursors is described