Grignard reagents

Organomagnesium halides, RMgX, having a carbon–magnesium bond (or their equilibrium mixtures in solution with R2Mg + MgX2).
Source:
PAC, 1995, 67, 1307 (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1338