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Chemistry · Glossary

What is Hydride donor?

Also known as: complex metal hydride

Definition 24.5 University Chemistry — Year 1 · Chapter 24 — Oxidation and Reduction in Organic Chemistry

A hydride donor transfers a hydrogen atom with its bonding pair, HX−\ce{H-}, to an electrophilic carbon. Sodium borohydride NaBHX4\ce{NaBH4} and lithium aluminium hydride LiAlHX4\ce{LiAlH4} are complex metal hydrides: the hydride is delivered from the BHX4X−\ce{BH4-} or AlHX4X−\ce{AlH4-} ion, not as a free ion.

Reduction of a ketone by borohydride: a B–H pair forms the new C–H bond while the C=O π pair goes to oxygen; the alkoxide is protonated by the solvent (water or an alcohol) or at the work-up. Each BH4- can deliver its four hydrogens in turn.
Reduction of a ketone by borohydride: a B–H pair forms the new C–H bond while the C=O π\pi pair goes to oxygen; the alkoxide is protonated by the solvent (water or an alcohol) or at the work-up. Each BHX4X−\ce{BH4-} can deliver its four hydrogens in turn.
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