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
Michaelis–Arbuzov reaction The displaced halide anion then usually reacts via another S2 reaction on one of the R carbons, displacing the oxygen atom to give the desired phosphonate (4) and another alkyl halide (5). This has been supported by the observation that chiral R groups experience inversion of configuration at the carbon center attacked by the halide anion. This is what is expected of an S2 reaction. Evidence also exists for a carbocation based mechanism of dealkylation similar to an S1 reaction, where the R group initially dissociates from the phosphonium salt followed by attack of the anion. Phosphite esters with tertiary