Why do halogen-metal exchanges happen?

Question

I'm trying to understand organometallic raegents but am stuck at halogen-metal exchanges.

Answer 1

Good question. The driving force is the desire of the base metal (Li or Mg) to lose electrons and become cations. This is very exothermic. Furthermore, the formation of free halide ions is also very exothermic.

In short, the group I or II metals are great reducing agents, and in the end, everyone is more stable energetically.