Apical functionalization of the [closo-B10H10]2- anion: Building blocks for modern materials

Abstract

This Review focuses on functionalization of the [closo-B10H10]2- anion in the apical positions in the context of the development of functional molecular materials. The most salient feature of the anion is its high lying HOMO (-4.14 eV, DFT), which due to its symmetry and distribution readily interacts with apical -substituents, and participates in intra- and inter-molecular photo-induced charge transfer processes. Such molecules are characterized by photonic and electronic properties, which can be controlled by judicious choice of substituents. Until recently, derivatives of the [closo-B10H10]2- with apical substituents (B(1) and B(10) substitution) were limited since most electrophilic substitution reactions give the equatorial products (B(2) substitution). The recent discovery of a fully selective phenyliodination reaction of the [closo-B10H10]2- anion has opened up access to a much greater variety of apical derivatives. This Review describes methods for apical substitution in [closo-B10H10]2- using mainly [closo-B10H8-10-X-1-N2]- and [closo-B10H8-10-X-1-IPh]- intermediates. It shows the scope of apical substituents connected with C, N, P, O, S, Se, and B atoms and halogens currently available through direct substitution and functional group transformations, and demonstrates their use as building blocks for emerging classes of functional materials.