Divalent metallylenes require ligands for stabilization. Ligands can stabilize metallylenes or enhance their reactivity through i) steric shielding or ii) electronic effects, via the inductive effect (e.g., by s-electron-withdrawing or s-electron-donating groups) or mesomeric effect (e.g. by lone pair donation). We will now primarily focus on increasing the reactivity by varying the ligands, while the stability of metallylenes will be addressed in a later section.