Reduction of metal carbonyls

Indirect electrosynthesis of reactive formyl transition metal compounds involves an initial step of reduction of metal carbonyls to radicals followed by transfer of a hydrogen atom from trialkyltin hydrides190. Electroreduction of metal carbonyls yields products of dimerization and loss of CO from the radical anion. Electroreduction in the presence of R3SnH yields the formylmetalcarbonyls ... 

Approximately 25 years after Mond and co-workers had prepared the first carbonyl of cobalt, Co2(CO)8 (78), Hieber obtained HCo(CO)4 by the acidification of salts containing [Co(CO)4] (79), one of the first established carbonylmetallates (80). In 1941, Behrens, a student of Hieber, initiated his important and extensive investigations on the reduction of metal carbonyls and their derivatives by alkali and alkaline earth metals in liquid ammonia (81). At this time he established that various salts of [Co(CO)4]-, including Na[Co(CO)4] and K[Co(CO)4], could be obtained from the neutralization of HCo(CO)4 or the reduction of Cd[Co(CO)4]2 by sodium or potassium in liquid ammonia (4). On the basis of Behrens pioneering studies, we were... 

II. Reduction of Metal Carbonyls with Alkali Metals and Sodium Tetra-... 

REDUCTION OF METAL CARBONYLS WITH ALKALI METALS AND SODIUM TETRAHYDRIDOBORATE IN LIQUID AMMONIA... 

The reduction of metal carbonyls or their derivatives with sodium in liquid NHS, begun by us 35 years ago, has become a method often used successfully by numerous other research groups throughout the world. A few examples are the preparation of Na2[7j5-C5H5V(CO)3] from 175-C5H5V(CO)4 (43) and [V-m(CO)5]s- and [M m(CO)3]3- (M = Co, Rh, Ir). According to Ellis et al. (44), these carbonyl metalates are obtained in the extremely low oxidation state of -III from the anions [V-1(CO) ]-and Co (CO)4] and also from the neutral complexes M3(CO)i2 (M = Rh, Ir). 

The alkali or alkali earth metals are often used for reduction of metal carbonyls in a variety of solvents. ... 

One frequently used solvent for the alkali metal reduction of metal carbonyls is liquid ammonia, in which alkali metals form blue solutions. These blue solutions are useful for some of the more drastic reductions, such as that of the very stable octahedral chromium hexacarbonyl to the anion [Cr(CO)s] ". Unfortunately, the reactivity of liquid ammonia toward most of the halide derivatives of interest for reaction with metal carbonyl anions has seriously limited its use in their preparation. Behrens and co-workers, however, have made an extensive study of the reactions of the [Cr(CO)5] anion prepared by the reduction of chromium hexacarbonyl with sodium metal in liquid ammonia these reactions will be discussed later. 

Sometimes mercury derivatives formed in the preparation of alkali metal carbonyls by reduction with sodium amalgam are potential contaminants in metal carbonyl derivatives prepared from the resulting sodium compounds. Moreover, in large-scale preparations the quantity of mercury required for the dilute amalgams can be very large and thus inconvenient. It is possible to avoid the presence of mercury in reductions of metal carbonyls such as Mn2(CO)io and Co2(CO)g by the use of lithium wire in tetrahydrofuran 38). 

Complexes which contain a transition metal in the anion may react with alkyl halides to yield <7-alkyl metal derivatives. Such anions are formed commonly by reduction of metal carbonyls or cyclopentadienyl metal carbonyls with sodium amalgam in tetrahydrofuran ... 

Ungurenasu and Palie b have reported a highly selective route to anionic binuclear complexes in greater than 99% yield by reduction of metal carbonyls with KCg. The reactions were carried out in dry, deoxygenated THF at25 C,Eqs. 9.10 and 9.11 ... 

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