hexamethyldisilazide

Hexamethyldisilazide refers to the hexamethyldisilazide anion, (Me3Si)2N−, as well as its metal salts such as LiHMDS, NaHMDS, and KHMDS. It is the conjugate base of hexamethyldisilazane (HMDS), a disilazane with the structure Me3Si–NH–SiMe3.

Commonly prepared by deprotonation of HMDS with alkali metal hydrides or amides, the salts are widely used as non-nucleophilic bases in organic synthesis. They are typically employed in aprotic solvents such as THF or toluene and can be used as solutions or as solid reagents.

Hexamethyldisilazide bases are bulky and highly basic, with limited nucleophilicity. They efficiently deprotonate carbonyl compounds to form enolates, and can generate carbanions and alkynyl anions from relatively acidic C–H bonds, often at low temperatures. The choice of metal cation (Li+, Na+, K+) influences aggregation and reactivity.

Applications include formation of enolates and allylic anions, as well as metallations of arenes and heteroarenes. NaHMDS and LiHMDS are common in pharmaceutical and materials synthesis due to their compatibility with sensitive functional groups.

Handling: air- and moisture-sensitive; store under inert atmosphere. Reagents may cause severe irritation; avoid contact.