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Camouflaged Carborarods Derived from B ‐Permethyl‐1,12‐diethynyl‐ para ‐ and B ‐Octamethyl‐1,7‐diethylnyl‐ meta ‐carborane Modules
Author(s) -
Herzog Axel,
Jalisatgi Satish S.,
Knobler Carolyn B.,
Wedge Timothy J.,
Hawthorne M. Frederick
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500339
Subject(s) - carborane , steric effects , chemistry , stereochemistry , solubility , molecule , vertex (graph theory) , computational chemistry , crystallography , organic chemistry , graph , combinatorics , mathematics
Rigid camouflaged carborarods constructed from the corresponding C , C ′‐diethynyl derivatives of B ‐decamethyl‐1,12‐dicarbadodecaborane(12) ( 6 ) and B ‐octamethyl‐1,7‐dicarbadodecaborane(12) ( 48 ) have been synthesized by largely conventional organic transformations. These carborarods are the longest discrete rod species available by this method in which B‐methylated p ‐carborane and m‐ carborane cages are linked through their carbon vertices by 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 average, 16 carborane modules. The structural characterization of the corresponding dimeric species revealed that the carborarods possess a sinusoidal chain distortion in the solid state. The stereoelectronic properties of these and related model carborarods were evaluated by using molecular dimensions as a monitor for the comparison of computational and experimental methods. In addition, the effect of exhaustive B‐methylation of 12‐ and 10‐vertex para ‐carborane cages in a series of model C , C ′‐diethynyl derivatives was similarly investigated by computational and structural studies. As expected, a correlation of intercage CC bond lengths with cage size was observed and was attributed to hybridization effects. B‐Permethylation had no significant structural effect with either 10‐ or 12‐vertex cage derivatives. Relative to unsubstituted compounds, thermal and chemical stabilities of B‐permethylated derivatives were increased through the operation of a steric “bumper‐car” process, and solubilities in organic solvents were enhanced. The formation of linear, sterically encumbered platina–carborarods using ethynyl derivatives of 6 as precursors is described.