Undergraduate organometallic courses often start with classical M(CO)n complexes of zero-valent transition metals which are exemplary in following the 18-electron rule. In the more advanced catalysis courses, zero-valent metal complexes also play a dominant role. In stark contrast, chemistry with zero-valent main group metal complexes is a curiosity. This is especially the case for the most electropositive s-block metals that easily lose their valence electrons, making isolation of zero-valent metal complexes a real challenge. However, most recent developments start filling this gap with the syntheses of first zero-valent s-block metal complexes (Figure 1). These complexes feature unusual metal-metal bonds and oxidation state assignments of the metals are ambiguous. Herein, an in-depth presentation of recent work on formally zero-valent alkaline-earth metal complexes is given.
