Oxidative addition reactions of heavy analogs of carbenes (germylenes, stannylenes, plumbylenes) to σ-bonds

Oxidative addition reactions are the key stage of catalytic transformations. This review presents a detailed discussion of the oxidative addition reactions of low-valent group 14 derivatives (Ge, Sn, Pb) to various sigma bonds, including HH, CH, H-Hal, HN, HSi, HB, Hal-Hal, P-Hal, PP, SS, OO. Furthermore, the features of oxidative addition reactions of tetrylenes with diverse substituents (C-, O-, N-, S-, B-bonded) are discussed from the viewpoint of relation to bond angles and HOMO-LUMO gaps. The direction and rates of oxidative addition reactions of tetrylenes strongly depend on the tetrel atom, as well as the presence of donor-acceptor interactions in tetrylene, the oligomeric state and bond angle values around the tetrel atom, and the value of the HOMO-LUMO gap. In general, the Ge(II) derivatives tend to form Ge(IV) oxidative addition products, the Sn(II) analogues often form Sn(II) bridging products; while the Pb(II) derivatives are less stable and prone to disproportionation reactions. The reactivity of C-substituted tetrylenes is influenced by the bond angle values and the HOMO-LUMO gap. The latter can be reduced by replacing one of the C-containing substituents with donor fragments. The reactivity of heteroleptic tetrylenes with acceptor substituents is reduced in oxidative addition reactions. The presence of intramolecular interactions between the tetrel atom and the donor molecules or functional groups of ligands can also alter the direction of oxidative addition reactions. The primary factor affecting the oxidative addition reactions of O-substituted tetrylenes is the monomeric or oligomeric state. Tetrylenes based on redox-active catecholate or o-amidophenolate ligands undergo oxidation of the redox-active ligand in the presence of halogens or compounds with weak OO bonds.