Metallihydridin

Metallihydridin is a term used in inorganic and organometallic chemistry to denote metal-hydride species in which hydrogen exists as a hydride ligand (H−) bound to a metal center. The expression is used in several European languages and broadly covers terminal hydrides, bridging hydrides that link two or more metals, and larger metal-hydride clusters.

Bonding and structure: In metallihydridins, the M–H bond is typically a strong sigma interaction, with bond strength and length depending on the metal, oxidation state, and surrounding ligands. Terminal hydrides feature a single M–H bond, while bridging hydrides are shared between two or more metals. In clusters, hydrido ligands can occupy interstitial sites and participate in multicenter bonding.

Synthesis and occurrence: Metallihydridins are prepared by reduction of metal halides or oxides with hydride donors, oxidative addition of H2 to low-valent metal fragments, or protonation of metal-alkyl or metal-oxo precursors. They are well represented in transition-metal chemistry and serve as key intermediates in catalytic cycles.

Reactivity and applications: Hydride ligands enable activation of small molecules, hydride transfer, and migratory insertion steps. Metallihydridins underpin homogeneous catalysts for hydrogenation, dehydrogenation, and related transformations, and they appear in routes to energy storage materials that rely on reversible H2 uptake and release. They also feature in materials chemistry as building blocks for hydrided frameworks.

Safety and handling: Many metallihydridins are air- and moisture-sensitive and may react vigorously with water or produce hydrogen gas on hydrolysis. They are typically handled under inert atmospheres using specialized glassware and protective equipment.