[50916-70-6] · C6H18BrMgNSi2 · Bromomagnesium Hexamethyldisilazide · (MW 264.59)
(base for selective formation of magnesium enolates)
Physical Data: white solid from ether of composition Mg2Br2[N(SiMe3)2]2.2Et2O, mp 98 °C.
Solubility: sol benzene, cyclohexane, and toluene; very sol ether.
Preparative Method: Hexamethyldisilazane is added to Ethylmagnesium Bromide in ether. Cooling to -20 °C produces white crystals in good yield.1
Although seldom used in comparison with Bromomagnesium Diisopropylamide, bromomagnesium hexamethyldisilazide has the unique feature of high solubility in organic solvents.
Bromomagnesium hexamethyldisilazide and bromomagnesium diisopropylamide were the most effective of several magnesium bases examined for selective formation of the more substituted silyl enol ether from ketones (eq 1). Less-hindered ketones gave mainly aldol products.2
The reagent reacts with hindered esters to give isolable complexes, with no evidence for enolate formation (eq 2).3
Michael Rathke & Robert Elghanian
Michigan State University, East Lansing, MI, USA