metallacarboranes

Metallacarboranes are a class of organometallic compounds in which a metal center is bound to a carborane cluster, typically a closo-1,2-dicarba-closo-dodecaborane framework such as C2B10H12. The carborane cage acts as a rigid, bulky ligand with multiple donor sites, allowing the metal to bond to carbon vertices in many cases, though metal–boron bonds and endohedral coordination are also observed. The resulting complexes can be neutral, cationic, or anionic, and many are isolable as discrete molecules.

Structural motifs in metallacarboranes vary. Metals such as cobalt, iron, nickel, and ruthenium are common, and the cages are often represented as C2B9H11 or C2B10H12 derivatives that can bear substituents. A notable subset comprises dicarbollide ions [M(C2B9H11)2]−, in which a single metal center binds to two carborane cages; methylcobaltabisdicarbollide MeCo(C2B9H11)2− is a representative example with wide use in research and industry.

Synthesis typically involves direct metal insertion into the carborane framework or substitution of a hydride or halide by a metal fragment, and characterization is commonly accomplished by X-ray crystallography and NMR spectroscopy. Metallacarboranes exhibit diverse reactivity and electronic structures, enabling catalytic applications in organic transformations and offering potential roles in boron neutron capture therapy, radiopharmaceuticals, and advanced materials due to their robust, polyhedral boron-rich cores.

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