organomagnesium

Organomagnesium compounds are a class of organomettalic reagents in which a carbon atom is bonded to magnesium. The most widely used members are Grignard reagents, with the general formula RMgX, where R is an alkyl or aryl group and X is a halogen (Cl, Br, I). They are highly reactive and play a central role in carbon–carbon bond formation in organic synthesis. Grignard reagents were developed by Victor Grignard in the early 20th century, a discovery that earned him the Nobel Prize.

Synthesis and structure

Grignard reagents are prepared by reacting an alkyl or aryl halide with magnesium metal in dry, anhydrous ether solvents such as diethyl ether or tetrahydrofuran (THF). The solvent coordinates to magnesium, stabilizing the highly polar RMgX bond. The resulting species behave as nucleophilic carbon reagents and are highly sensitive to moisture and air.

Reactions and applications

Organomagnesium compounds participate in a wide range of transformations. They react with water or alcohols to give alkanes and magnesium salts, highlighting their strong basicity. They add to aldehydes and ketones to form secondary and tertiary alcohols after workup, with formaldehyde giving primary alcohols. Reaction with carbon dioxide yields carboxylic acids after acidic workup. Grignard reagents also react with epoxides to yield alcohols with chain extension, and with esters to form tertiary alcohols via acyl substitution. In practice, they are used to construct new carbon–carbon bonds and as building blocks for complex molecules.

Safety and limitations

Grignard reagents are highly reactive and moisture- and air-sensitive, often pyrophoric, and require inert atmosphere handling and dry solvents. They are incompatible with many functional groups (e.g., strong acids, protic solvents) and must be carefully quenched and disposed of.