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
Mercury(II) cyanide evaporated to crystallize the product. Hg(CN) can also be prepared by mixing HgO, finely powdered Prussian blue. In addition, it can be produced by reacting mercuric sulfate with potassium ferrocyanide in water: Another method to generate mercuric cyanide is through the disproportionation of mercury(I) derivatives. In these reactions, metallic mercury precipitates, and Hg(CN) remains in solution: Mercury cyanide can be used as a promoter in the Koenigs–Knorr reaction for the synthesis of glycosides. Cyanogen, (CN), forms upon heating dry mercury cyanide but the method is inferior to other routes: Coordination polymers can be synthesized from Hg(CN) building blocks. Large single