chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

, a metalloborane is a compound that contains one or more metal atoms and one or more

boron hydride Diborane(6), commonly known as diborane, is the chemical compound with the formula . It is a highly toxic, colorless, and pyrophoric gas with a repulsively sweet odor. Given its simple formula, borane is a fundamental boron compound. It has attr ...

. These compounds are related conceptually and often synthetically to the boron-hydride clusters by replacement of BH_n units with metal-containing fragments. Often these metal fragments are derived from

metal carbonyl A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. These properties are all associated with having electrons available at the Fermi level, as against n ...

s or

cyclopentadienyl complex A cyclopentadienyl complex is a coordination complex of a metal and cyclopentadienyl groups (, abbreviated as Cp−). Cyclopentadienyl ligands almost invariably bind to metals as a pentahapto (''η''5-) bonding mode. The metal–cyclopentadien ...

es. Their structures can often be rationalized by

polyhedral skeletal electron pair theory In chemistry the polyhedral skeletal electron pair theory (PSEPT) provides electron counting rules useful for predicting the structures of clusters such as borane and carborane clusters. The electron counting rules were originally formulated by ...

. The inventory of these compounds is large, and their structures can be quite complex.

Examples

Two simple examples are . The MB₄ cores (M = Fe or Co) of these two compounds adopt structures expected for nido 5-vertex clusters. The iron compound is produced by reaction of diiron nonacarbonyl with pentaborane. and

cyclobutadieneiron tricarbonyl Cyclobutadieneiron tricarbonyl is an organoiron compound with the formula Fe(C4H4)(CO)3. It is a yellow oil that is soluble in organic solvents. It has been used in organic chemistry as a precursor for cyclobutadiene, which is an elusive species i ...

have similar structures.

Metallacarboranes

Even greater in scope than metalloboranes are metallacarboranes. These cages have carbon vertices, often CH, in addition to BH and M vertices. A well-developed class of metallacarboranes are prepared from

dicarbollide In organometallic chemistry, a dicarbollide is an anion of the formula 2B9H11-. Various isomers exist, but most common is 1,2-dicarbollide derived from ortho-carborane. These dianions function as ligands, related to the cyclopentadienyl ani ...

s, anions of the formula ₂B₉H₁₁sup>2-. These anions function as ligands for a variety of metals, often forming

sandwich complex In organometallic chemistry, a sandwich compound is a chemical compound featuring a metal bound by hapticity, haptic, covalent bonds to two arene compound, arene (ring) ligands. The arenes have the formula , substituted derivatives (for example ...

es. Some metalloboranes are derived by the metalation of neutral

carborane Carboranes (or carbaboranes) are electron-delocalized (non-classically bonded) clusters composed of boron, carbon and hydrogen atoms.Grimes, R. N., ''Carboranes 3rd Ed.'', Elsevier, Amsterdam and New York (2016), . Like many of the related boron ...

s. Illustrative are the six-and seven-vertex cages prepared from ''closo''-. Reaction of this carborane with iron carbonyl sources gives ''closo'' Fe- and Fe2-containing products, according to these idealized equations: : : A further example of insertion into a closo carborane is the synthesis of the yellow-orange solid closo-1,2,3-: : A closely related reaction involves the capping of an anionic nido carborane : :{{chem2, Na(nido\sB4H7) + CoCl2 + NaC5H5 -> closo\s(C5H5)CoB4H6 + 2 NaCl + ... The last reaction is worked up with acid and air.

References

Cluster chemistry