Metal carbonyl 18-electron complexes is sometimes catalysed by catalytic amounts of oxidants, via electron-transfer. Metal carbonyls react with reducing agents such as metallic sodium or sodium amalgam to give carbonylmetalate (or carbonylate) anions: For iron pentacarbonyl, one obtains the tetracarbonylferrate with loss of CO: Mercury can insert into the metal-metal bonds of some polynuclear metal carbonyls: The CO ligand is often susceptible to attack by nucleophiles. For example, trimethylamine oxide and bistrimethylsilylamide convert CO ligands to CO and CN, respectively. In the "Hieber base reaction", hydroxide ion attacks the CO ligand to give a metallacarboxylic acid, followed by the release of carbon
Metal peroxide are generally formulated for peroxide salt. In excess of dilute acids or water they release hydrogen peroxide. Upon heating, the reaction with water leads to the release of oxygen. Upon exposure to air, alkali metal peroxides absorb CO to give peroxycarbonates. Unlike the alkali metal and alkaline earth metal peroxides, binary transition metal peroxides, i.e., compounds containing only metal cations and peroxide anions, are rare. Metal dioxides are pervasive, e.g. MnO and rutile (TiO), but these are oxides, not peroxides. Well characterized examples include the d metal cations, Zinc peroxide (ZnO), two polymorphs, both explosive, of mercury peroxide (HgO), and