Carboranes

Carboranes are a class of boron hydride clusters in which one or more of the BH vertices are replaced by CH units. Of all the known carboranes, the icosahedral o-carboranes have been the most extensively investigated because of their commercial availability, though the first o-carboranes were reported in the open literature in late 1963. Over half a century, the chemistry of carboranes has experienced tremendous growth with new synthetic methodologies, novel structures, new bondings and various applications. This themed issue celebrates the 50^th anniversary of the discovery of o-carboranes by bringing together manuscripts from authors around the world.

o-Carboranes can be converted into nido-C₂B₉H₁₁²⁻ by selective removal of a BH vertex, nido-C₂B₁₀H₁₂²⁻ or arachno-C₂B₁₀H₁₂⁴⁻via reduction with group 1 metals. These anions are excellent π ligands for transition metals or serve as useful synthons for the preparation of supraicosahedral carboranes/heterocarboranes through polyhedral expansion methodology. On the other hand, o-carboranes can undergo deprotonation reaction to give either monoanion LiC₂B₁₀H₁₁⁻ or dianion Li₂C₂B₁₀H₁₀²⁻, which react further with electrophiles to generate a class of carborane-based ligands for transition metals. In addition, o-carboranes can also be functionalized via o-carborynes (1,2-dehydro-o-carboranes) intermediates. These functional carboranes are finding applications in materials science as building blocks and in medicine as potent boron neutron capture therapy agents.

The collection of papers presented in this themed issue encompasses all aspects aforementioned across a broad spectrum of carborane derivatives, reflecting the current research interests in this field. We hope that readers will find this timely collective volume interesting and stimulating. We would like to take this opportunity to thank all contributors, reviewers, and the editorial team for their high quality and professional work.

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