Reduction by metals and amalgams

Half reaction (acidic solution) Standard reduction 1 potential, E°,V 1 

In anionic carbonyl complexes the metal center is often found in a negative oxidation state and this is reflected in the standard potentials of metal carbonyls. Thus, the standard potentials of the following couples are -0.68, -0.40, and -0.74 V, respectively, Eqs. 9.1 - 9.3  

Syntheses of the carbonyl anions are most often carried out with alkali metals or their amalgams. For example, the complex, Na[Fe(CO)2(C5H4Me)], is obtained as a result of reduction of the dimer, [Fe(CO)2(C5H4Me)]2, by sodium amalgam in THF.6 The reactions of [M(CO)3Cp] (M = Nb, Ta) with metallic sodium in liquid ammonia give Na2[M(CO)3Cp].2 Loubster and Lotz carried 

Sodium amalgam is used widely to reduce homobinuclear carbonyl or nitrosyl organometallic complexes. Such reduction results in the formation of anionic compounds. For example, [Co2(CO)s] is reduced in tetrahydrofuran with sodium amalgam producing Na[Co(CO)4]. Several investigators - have carried out reactions of this type, Eq. 9.4  

The reduction of metal complexes is accompanied often by dimerization and/or by formation of compounds with metal-metal bonds. For example, the reduction of [FeBr(CO)2(il -C5(p-tol)5)] with zinc powder in 

---