Condensation redox

For mixed carbonyl adducts, from other groups, redox condensation reactions have been employed to considerable effect. Thus for osmium-cobalt, a range of derivatives has been prepared (241, 248, 249) by reactions of the types ... 

Chini has recently reported the redox condensation between Fe3(CO)12 and the anion [Co(CO)4] to yield the anion [Fe3Co(CO)13] , but no details of the structure or stability of the complex are cited (234). 

The synthesis of [Fe4(CO)i3]2- (structure in Fig. 10) has been extensively studied by Hieber and co-workers. The reaction of a variety of ligands1 1 with Fe(CO)s results in redox condensation reactions and formation of the dark red dianion [Fe4(CO)I3]2... 

The first mixed carbonyl, the anion [FeCo3(CO)i2]-, was obtained using the redox condensation shown in Eq. (63)52. ... 

The redox condensation shown in Eq. (9) gives rise to the dianion [Fe3Ni(CO)12]2 and it has also been possible to isolate salts of the corresponding hydride, [Fe3Ni(CO)12H]- (30.5 r). The presence of infrared absorptions due to bridging carbonyls and the complexity of the infrared spectrum indicate a structure similar to Co4(CO)i2 with the nickel in the basal plane171). 

Scheme 8 summarizes the introduction of the missing carbon atoms and the diastereoselective epoxidation of the C /C double bond using a Sharpless asymmetric epoxidation (SAE) of the allylic alcohol 64. The primary alcohol 62 was converted into the aldehyde 63 which served as the starting material for a Horner-Wadsworth-Emmons (HWE) reaction to afford an E-configured tri-substituted double bond. The next steps introduced the sulfone moiety via a Mukaiyama redox condensation and a subsequent sulfide to sulfone oxidation. The sequence toward the allylic alcohol 64 was com-... 

Dodecacarbonyltetraruthenium dihydride, redox condensations, 30 157 Dodecacarbonyltriosmium pyrolysis reactions, 30 143 reduction, 30 151... 

Related synthetic routes include the redox condensation reaction of carbonylate anions with neutral carbonyls, e.g., Eq. (12) (55), metal exchange reactions between carbonylate anions, e.g., Eq. (13) (56), and direct reductive carbonylation of metal halides, e.g., Eq. (14) (57). The stoichiometry of the products are not rational, and the mechanisms clearly are very complicated, though once again these reactions, under experimental optimization, can provide very useful synthetic routes. 

This particular reaction may proceed via the initial disproportionation of Co2(CO)8 to give [Co(CO)4] which then undergoes redox condensation with Fe(CO)5. 

The reaction of a carbonylmetalate with a neutral metal carbonyl has been labeled a redox condensation by Chini et al. (40, 41) and has been as widely used as a pyrolysis reaction for synthesizing mixed-metal clusters. Carbonylmetalates usually react rapidly with most neutral carbonyls, even under very mild conditions. A large number of mixed-metal hydride clusters have been formed via this type of reaction, primarily because the initial products are anionic clusters that in many cases may be protonated to yield the neutral hydride derivative. 

On the basis of mechanism, condensation processes can be divided into two broad categories (a) reactions induced by coordinatively unsaturated species and (b) reactions between coordinatively saturated species in different oxidation state (redox condensation). 

The relevance of redox condensation, which by contrast generally requires very mild conditions, began to emerge slowly after 1965 (15, 110) when Hieber and Shubert reported the first example of such a reaction (78) ... 

Redox condensation is not restricted to the reaction of a carbonylmetal-ate with a neutral carbonyl, and it is possible to condense the carbonyl-metalate with other simple cationic species for example (35,102),... 

Redox condensation between anionic and cationic species is often highly dependent on the medium, and the use of less basic solvents of high steric requirements, which do not coordinate strongly to the cationic center, may result in a marked improvement in the ease of condensation (35). 

The following are further examples of redox condensations, showing the general possibility of such a reaction between species in different oxidation states (99,101) ... 

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