text: Many electrophilic oxides insert into metal carbon bonds; these include sulfur dioxide, carbon dioxide, and nitric oxide. These reactions have limited or no practical significance, but are of historic interest. With transition metal alkyls, these oxides behave as electrophiles and insert into the bond between metals and their relatively nucleophilic alkyl ligands. As discussed in the article on Metal sulfur dioxide complexes, the insertion of SO has been examined in particular detail. SO inserts to give both O-sulphinates and S-sulphinates, depending on the metal centre. With square planar alkyl complexes, a pre-equilibrium is assumed involving formation of an adduct.