This critical review covers recent developments in the special chemistry which can take place when two different s-block metals are combined within the same organometallic mixture or reagent. It will cover a selection of the most widely researched mixed-metal â synergicâ systems, and will be confined to mixed alkali metal/magnesium reagents. An overview of the known structural chemistry of these fascinating systems will be presented along with some of their pertinent, recent uses in synthesis, including, in the activation/cleavage of C-H bonds (i.e., a metallation reaction) or induction of metal-halogen exchange in organic molecules. The chapter begins by providing a brief historical overview of mixed s-block metal chemistry.