Carbenoid Reactions Promoted by Solids: From Lewis to Brønsted Catalysts.

ConspectusDiazocarbonyl compounds have become essential tools in organic synthesis, due to their ability to in situ generate reactive carbenes and be inserted in a variety of otherwise stable bonds, such as C-H, C-C, H-O, and so on. However, a soluble metal salt or complex catalyst is generally required to selectively activate and couple the carbene, and the metals employed so far are expensive (Rh, Au, Ag, Cu) and often unrecoverable. It is noteworthy that the price of ligands can make a cheaper metal catalyst (i.e., Cu) as expensive as other ligand-free noble metal catalysts. In the realm of modern sustainable chemistry, most of these methodologies are now unacceptable and must be adapted, and simple strategies for that include carbene photoactivation and the use of recoverable solid catalysts. Unfortunately, despite research in the field of carbene insertion reactions that has extended now for more than 50 years, examples with solid catalysts are still minor, and efficient solid catalysts have only been reported in the last two decades.This Account shows the journey faced by our group in the last eight years to find solid catalysts for challenging carbene insertion reactions, employing diazocarbonyl compounds as carbene precursors. We will contextualize our results with those of previous solid catalysts. The discovery in 2017 that a quasi-linear Pd