Reduction, induced carbonyl substitution

Photo-induced additions of ferrocene to electron-deficient alkynes, giving 1-ferrocenylalkenes, photo-ethoxycarbonylation of ferrocene derivatives ( v-CCU-EtOH), and electrochemically-initiated additions of alkyl radicals (from RCOg ) to ferricenium cation have been reported. Electrochemical reductive cleavage of the ring-metal bonds in carbonyl-substituted ferrocenes has been achieved using polarographic methods. ... 

Two other functionally substituted 17-cyclopentadienyl titanium dicarbonyl complexes prepared by Rausch and co-workers include the vinyl Cp compound (i7-C5H4CH=CH2)CpTi(CO)2 (81) and the carbomethoxy Cp compound (rj-C5H4C02Me)CpTi(C0)2 (82). Both were synthesized via the aluminum-induced reductive carbonylation of the corresponding dichloride derivatives. 

The [Rh(CO)2Cl]2-induced ring fission of substituted cyclopropanes 8a-b affords the rhodium complexes 9a-b via carbonylation [8]. The regioselectivity of carbonyl group insertion depends on the substituent. Reduction with NaBH4 leads to the corresponding alcohol. (Scheme 4)... 

Chromium hexacarbonyl is extremely photolabile (equation 6) therefore photochemical substitution is an efficient means of preparing derivatives. Oxidation of the Cr center requires nitric or sulfuric acid, or chlorine. Alternatively, some hgands induce complete carbonyl dissociation with concomitant oxidation, for example, acetylacetonate. Chemical reduction with alkali or alkaline-earth metals or electrochemical reduction proceeds in two-electron steps with loss of two CO molecules to first give [Cr2(CO)io]" and then [Cr(CO)s]. Nucleophilic attack at CO generates a number of stable (Nu = R) and unstable (Nu = N3, OH, H, NEt2) products. The stable [(OC)5CrCOR] ion is a carbene precursor. 

The catalytic substitution reactions of metal carbonyl clusters, including [M3(CO)i2] (M = Fe, Ru, or Os), [Ru4H4(CO)i2], [Rh6(CO)i6], and [Co3(CO)9(/it-CCl)], with isocyanides or Group V-donor ligands may be induced by either electrochemical or chemical (benzophenone ketyl) reduction. The most favorable conditions for efficient substitution include (1) the formation of a radical anion with a significant lifetime and (2) the use of a ligand which is not reduced by [Ph2CO], and which is less of a tt acid than CO (166). 

---