Decakis(dichloroniethyl)-l,12-dicarba-closo-dodecaborane(12): Camouflage of an Icosahedral Carborane by L'sing Bulky Functional Substituents

摘要

The icosahedral carboranes constitute a class of structurally unique molecules with properties common to both organic and polyhedral borane chemistry. Their exceptional thermal and chemical stabilities and their ability to hold substituents in rigidthree-dimensional spatial orientations has made their derivatives desirable synthetic targets for modular chemistry. In contrast to the well-developed chemistry of the CH vertices of the carboranes, substitution reactions that occur at UH vertices tendtobe less straightforward and of limited utility due to a lack of regiospecific control. Thus, electrophilic substitution reactions at BH vertices typically lead to mixtures of products. Under robust conditions, however, substitution of ali available BHvertices may occur to give a single final product. Thus, we have developed a synthetic procedure that leads to a class of 1,12-dicarba-closo-dodecaborane derivatives (para-carborane derivatives), which are methylated at all boron vertices and which alsomay have none, one. or both of the two CH vertices similarly substituted. Molecules of this class are structural hybrids composed of an icosahedral carborane substructure covered by an external sheath of hydrocarbon. Consequently, the general reactivityof these molecules should resemble that of aliphatic hydrocarbons, although the steric constraints placed upon the aikyl groups present in these species would be expected to control reactivity in a manner not exhibited by simple alkanes. Functionulizationof the full array of alkyl groups on the icosahedral framework will generate an outer sphere of molecular camouflage composed of reactive organic groups of great importance to the further elaboration of carborane chemistry. Depending upon the specific substituent groups introduced, such compounds should be accessible for modular syntheses and serve as precursors for other derivatives, as well. We here report an enin into this chemistry. Beginning with decamethyl)-1,12-dicarba-closos-dodecaborane(12) (1), we have synthesized a derivative in which all the methyl groups at the boron centers are haiogenated under radical-inducing conditions to afford deca-kis ( dichloromethyl) - 1.12- dicarba - closo - dodecaborane(12) (2). which has been structurally characterized by X-ray diffraction studies (see Fig. 1).