The breaking and formation process of chemical bonds is the most important research content in the field of chemistry. As one of the most important branch of chemical bonds, the study of metal-metal bonds is of significant importance in further expanding our understanding of the structure of substances, the nature of the chemical bond and the essence of catalytic transformation. To date, the research of metal-metal bonds mainly focuses on d-block, p-block, and f-block elements. However, it is more difficult to form the metal-metal bonds due to the s-block alkaline earth metal elements with low electro- negativity can easily lose two valence electrons, resulting in the challenge of construction complexes containing alkaline earth metal-metal bonds. The recent progress in alkaline earth metal-metal bonds is reviewed, which are mainly focus on the synthesis, structure and reactivity of alkaline metal-metal bonds according to the different bonding elements. Finally, the future developments and applications in this field are also prospected.

Key words: metal-metal bond, alkaline earth metal, organometallic complex, synthesis, structure