dihydride

Dihydride is a term used in chemistry to describe a species that contains two hydride ligands (H−). In organometallic chemistry, it most commonly refers to metal dihydride complexes, where two hydride ligands are bound to a central metal atom. The two hydrides may be terminal, both bound directly to the metal, or they may act as bridging hydrides in clusters or multinuclear frameworks.

Structural and electronic features: In dihydride complexes, the surrounding ligands (such as phosphines, carbonyls, or cyclopentadienyl groups) influence the geometry and the relative positions of the hydrides. Dihydrides can be described as either cis or trans with respect to other ligands, and in some systems the hydrides may bridge between two metal centers, forming μ-hydride motifs.

Formation and reactivity: Dihydride species are often generated by the oxidative addition of H2 to a lower-valent metal complex or by hydride transfer to a metal center. They commonly arise as intermediates in catalytic processes such as hydrogenation, hydrofunctionalization, and other hydride transfer reactions. Their reactivity as hydride donors makes them important in reducing substrates and in regenerating active catalytic species.

Applications and characterization: Dihydrides are central to many catalytic cycles in organometallic chemistry. Characterization typically involves infrared spectroscopy to observe metal–hydride vibrations and nuclear magnetic resonance to detect hydride signals, which often appear at characteristic upfield shifts. X-ray crystallography can confirm the exact geometry of the hydride ligands.

See also: metal hydride, hydride transfer, hydrogenation, dihydrogen complex.