The versatile chemistry of the [B20H18]2- ions: novel reactions and structural motifs

Among the polyhedral closo-BnHn]2- ion series (n = 5-12 inclusive) the aromatic closo-B10H10]2- ion is both readily available and quite reactive. Among its many reactions which retain its cage structure one finds the oxidative dimerization reaction in which two closo-B10H12]2- ions each formally lose a hydride ion and undergo dimerization of the resulting closo-B10H9]- ions to produce the trans-B20H18]2- ion. The two-component closo-B10H9]- ions of the latter are linked together by a pair of unique B-B-B bonds which provide unprecedented reactivity to the structure. Among these reactions are the two-electron reduction to a set of three interconvertible B20H18]4- ions having intercage B-B bonds and the related reductive substitution reaction in which trans-B20H18]2- undergoes attack by nucleophile, L, to produce B20H18L]2-. The latter species is formally a substituted B20H19]3- (L = H) ion formed by B-B bond protonation of one of the isomeric B20H18]4- ions. These and a variety of novel reactions are described here along with interrelated reaction mechanisms considered for the first time.