Practical Synthesis of 1,12-Difunctionalized o-Carborane for the Investigation of Polar Liquid Crystals

Abstract

Two isomerically pure 1,12-difunctionalized derivatives of o-carborane, 12-iodo-1-vinyl (1b) and 12-iodo-1-phenyl (1c), are conveniently obtained on a practical scale in yields of 22% and 32%, respectively, by monoiodination of the corresponding o-carborane derivatives (4b and 4c) followed by separation of the regioisomers by crystallization (1b) and chromatography (1c). Subsequent functional group transformations gave access to other derivatives, including two liquid-crystalline compounds, in which o-carborane is a linear structural element. Regioselectivity of substitution on the carborane cage and on the benzene ring correlates with the inductive effect parameter of the substituent. The preparation of analogous derivatives of m-carborane was also investigated.

Carboranes in the chemist's toolbox

“…63 Among a number of important topics not specifically covered are nonlinear optical materials, [166][167][168][169][170][171][172] liquid crystals, [173][174][175][176][177][178][179] and ionic liquids, 180 among others. I have barely scratched the surface of the burgeoning field of biomedical applications, on which a formidable literature has accumulated.…”

“…I have barely scratched the surface of the burgeoning field of biomedical applications, on which a formidable literature has accumulated. 63 Among a number of important topics not specifically covered are nonlinear optical materials, [166][167][168][169][170][171][172] liquid crystals, [173][174][175][176][177][178][179] and ionic liquids, 180 among others. What should be clear from this discussion is the versatility of carboranes and metallacarboranes as tools that can be applied to a broad range of problems in the laboratory and in the realm of applied technology.…”

o-Carborane derivatives for probing molecular polarity effects on liquid crystal phase stability and dielectric behavior

“…Recently, we have reported practical access to isomerically pure 1,12-difunctionalized derivatives of o-carborane, 16 which opened up the door to investigation of new classes of liquid crystals of type IB. In this context two such derivatives, 1[B]a and 2[B]e (Fig.…”

“…In this context two such derivatives, 1[B]a and 2[B]e (Fig. 2), were prepared and their preliminary studies indicated a significant smectogenic character, 16 which warrants further detailed investigation. Here we describe the synthesis and characterization of a series of isostructural derivatives 1 and 2 (Fig.…”

Synthesis and Crystal Structure of 9,12-Dibromo-ortho-Carborane

“…It should be noted that to date, a large number of various iodo derivatives of carboranes have been synthesized, differing in the position of the substituents and their number [20][21][22][23][24][25][26][27][28][29][30]. The increased interest in iodine derivatives of carborane is mainly caused by their use in various cross-coupling reactions [21][22][23][31][32][33][34][35][36][37][38][39][40], as well as in study of intermolecular hydrogen and halogen bonding [41,42] and medicinal chemistry [43]. Despite the fact that the bromination of carboranes was first described as early as the mid-1960s [44], the chemistry of bromo derivatives of carboranes has been studied to a much lesser extent compared to the iodo derivatives.…”