Abstract
Hydrogenation is among the most widely used transformations in chemical synthesis, yet it typically relies on precious transition-metal catalysts, pressurised hydrogen gas and an excess of solvents. Here we report a solvent-free, transition-metal-free hydrogenation method based on mixtures of simple, commercially available calcium salts (CaH
2
with Ca(OH)
2
or CaCO
3
). Under mechanochemical conditions, calcium hydride reacts with calcium hydroxide or carbonate to generate H
2
in situ, eliminating the need for an external hydrogen source. The system efficiently hydrogenates alkenes, alkynes and aromatic hydrocarbons, including tetrasubstituted alkenes and benzene. Mechanistic studies support reversible hydrocalciation at the calcium hydride surface followed by irreversible hydrogenolysis with in situ generated H
2
. The method was demonstrated to be general, with the hydrogenation of 16 examples proceeding with an average of 74% yield, providing a safe, cheap and practical alternative to transition metal-catalysed hydrogenation of carbon-carbon multiple bonds.