Hydrido

Hydrido is the term used in several languages (for example, Spanish hidrido or Portuguese hidreto) to refer to what in English is called a hydride. In chemistry, a hydrido can denote either a hydride ion (H−) or a hydrogen atom bound to a metal center as a hydrido ligand (M−H) in a coordination or organometallic complex. Hydrido ligands are common in transition-metal chemistry and often play a key role in catalytic cycles and hydrogen transfer processes.

Hydrides are broadly categorized by their bonding and origin. Ionic or ionic-like metal hydrides, such as sodium hydride (NaH) and calcium hydride (CaH2), feature hydrogen in a negative oxidation state closely associated with a metal cation. Molecular or covalent hydrides involve hydrogen bound to nonmetals or to metals in a covalent framework, but the defining feature remains hidridic hydrogen capable of acting as a hydride donor. In many practical contexts, borohydride (BH4−) and aluminium hydride (AlH4−) species are important as hydride sources in synthesis.

Preparation and reactivity vary by type. Ionic hydrides can be formed by direct reaction of hydrogen with alkali or alkaline earth metals, while molecular hydrides and hydride donors are generated or tuned for reactivity through reduction chemistry and salt metathesis. Hydrido ligands are typically strong nucleophiles and reductants, enabling hydride transfer to carbonyl compounds, imines, and other electrophiles. In biology and biochemistry, hydride transfer reactions—such as those involving NADH/NAD+—are central to energy metabolism and reductive biosynthesis.

Applications include bases and reducing agents in organic synthesis, hydrogen storage contexts, and catalytic processes where metal–hydride intermediates mediate transformations. See also hydride, hydricity, hydrogen storage, and NADH.