Pure and Applied Chemistry

Abstract: The continued growth of polyhedral borane chemistry is illustrated by the successful synthesis of [closo-B₁₂(OH)₁₂]² –by the H₂O₂ oxidation of [closo-B₁₂H_12,]₂. The hydroxylated species reacts with common organic reagents to produce 12-fold degenerately substituted carboxylate esters, ethers, and carbamate esters. The ether derivatives undergo facile and reversible redox reactions in which the B12 scaffold serves as a one-or two-electron donor giving stable oxidation states described by [closo -or hypercloso-B₁₂OR)₁₂]ⁿ with n = −2,−1,and 0. The loss of polyhedral electrons is compensated by back-bonding from the attached ether oxygen substituents. Structural comparisons are presented along with representative reaction chemistry. Derivatives that bear functional groups on the termini of the 12-fold set of substituents provide a vast array of potential applications. To distinguish these new polyfunctional icosahedral species from dendrimers,they have been designated as closomers.