Ferrocene nitration

The most notable chemistry of the biscylopen-tadienyls results from the aromaticity of the cyclopentadienyl rings. This is now far too extensively documented to be described in full but an outline of some of its manifestations is in Fig. 25.14. Ferrocene resists catalytic hydrogenation and does not undergo the typical reactions of conjugated dienes, such as the Diels-Alder reaction. Nor are direct nitration and halogenation possible because of oxidation to the ferricinium ion. However, Friedel-Crafts acylation as well as alkylation and metallation reactions, are readily effected. Indeed, electrophilic substitution of ferrocene occurs with such facility compared to, say, benzene (3 x 10 faster) that some explanation is called for. It has been suggested that. 

Farnesol, 56,112 Ferric chloride, 57,17 Ferric nitrate, 57,66 Ferrocene, 56,28... 

Eerrocene (1) was the first sandwich complex to be discovered, thereby opening a wide and competitive field of organometallic chemistry. The formation of ferrocene was found at almost the same time in two independent studies on July 11, 1951, Miller, Tebboth, and Tremaine reported that on the passage of N2 and cyclopenta-diene over a freshly prepared mixture of reduced Ee (90%), alumina (8%), potassium oxide (1%), and molybdenum oxide (1%) at 300°C, yellow crystals identified as Cp2Ee (Eig. 1) were obtained [1]. Due to the low yields obtained (3 g starting from 650 g ferric nitrate), doubts remain as to whether Ee(0) was the... 

The ferrocene moiety is not just an innocent steric element to create a three-dimensional chiral catalyst environment. Instead, the Fe center can influence a catalytic asymmetric process by electronic interaction with the catalytic site, if the latter is directly coimected to the sandwich core. This interaction is often comparable to the stabilization of a-ferrocenylcarbocations 3 (see Sect. 1) making use of the electron-donating character of the Cp2Fe moiety, but can also be reversed by the formation of feirocenium systems thereby increasing the acidity of a directly attached Lewis acid. Alternative applications in asymmetric catalysis, for which the interaction of the Fe center and the catalytic center is less distinct, have recently been summarized in excellent extensive reviews and are outside the scope of this chapter [48, 49], Moreover, related complexes in which one Cp ring has been replaced with an ri -arene ligand, and which have, for example, been utilized as catalysts for nitrate or nitrite reduction in water [50], are not covered in this chapter. 

Gomez Arrayas R, Adrio J, Carretero JC (2006) Recent applications of chiral ferrocene ligands in asymmetric catalysis. Angew Chem Int Ed 45 7674—7715 Dai LX, Hou XL (2010) Chiral ferrocenes in asymmetric catalysis. Wiley-VCH, Weinheim Rigaut S, Delville MH, Losada J, Astrac D (2002) Water-soluble mono- and star-shaped hexanuclear functional organoiron catalysts for nitrate and nitrite reduction in water syntheses and electroanalytical study. Inorg Chim Acta 334 225-242... 

Addition of mercury(II) nitrate solution to ethanol gives mercury fulminate. Ferrocene... 

Sallott, G. P. et al., Proc. Int. Pyrotech. Semin., 1984, 589-602 Compositions prepared from mercury(II) nitrate and ferrocene or its derivatives show promise as explosive priming mixtures, but such mixtures are fairly sensitive to electrostatic initiation and should be handled in the wet state. 

Equation (1) is generally used to estimate the rate constant, kin the micellar pseudophase, but for inhibited bimolecular reactions it provides an indirect method for estimation of otherwise inaccessible rate constants in water. Oxidation of a ferrocene to the corresponding ferricinium ion by Fe3 + is speeded by anionic micelles of SDS and inhibited by cationic micelles of cetyltrimethylammonium bromide or nitrate (Bunton and Cerichelli, 1980). The variation of the rate constants with [surfactant] fits the quantitative treatment described on p. 225. Oxidation of ferrocene by ferricyanide ion in water is too fast to be easily followed kinetically, but the reaction is strongly inhibited by anionic micelles of SDS which bind ferrocene, but exclude ferricyanide ion. Thus reaction occurs essentially quantitatively in the aqueous pseudophase, and the overall rate depends upon the rate constant in water and the distribution of ferrocene between water and the micelles. It is easy therefore to calculate the rate constant in water from this micellar inhibition. 

Aminoferrocene (XXXV) can be prepared in low yield by treatment of O-methylhydroxylamine or O-benzylhydroxylamine with ferrocenyllithium (1, 65). Nitroferrocene (XXXVI), unattainable by direct nitration of ferrocene, can be isolated from the reaction of ferrocenyllithium and either n-propyl nitrate or dinitrogen tetroxide at —70° (30, 36). A similar reaction between ferrocenyllithium and nitrous oxide leads to azoferrocene (XXXVII) (08). 

Stronger conditions of oxidation lead to complete rupture of the cyclopenta-dienyl-iron bond. Attempts to nitrate ferrocene using ethyl nitrate in the presence of sodium alkoxides led to considerable amounts of nitrocyclopentadienylsodium and iron oxides (118). Treatment of ferrocene with bromine or chlorine is also reported to result in destruction of the ferrocene nucleus, the products containing pentahalocyclopentanes (64). 

Other reactions typical of aromatic systems, such as nitration and bromination, arc not feasible with metallocenes because of their sensitivity to oxidation.,h- However. many of the derivatives that would be produced in these types of reactions can be made indirectly by means of another reaction typical of aromatic systems mctalla-lion. Just as phenyllithium can be obtained from benzene, analogous ferrocene compounds can be prepared ... 

Direct nitration and halogenation leads to the decomposition of ferrocene. The processes are, therefore, carried out indirectly as described below... 

On the contrMy, ferrocene, (C5H5)2Fe, cmi be nitrated with difficulty. This is explained by formation of cation (C5H5)2Fe+ with reduced activity towards electrophilic agents. 

It is well known that electron-donating groups attached to benzene greatly enhance the ring s reactivity towards electrophilic substitution reactions, whereas electron-attracting groups decrease such reactivity markedly. Like most aromatic systems, ferrocene undergoes electrophilic substitution reactions readily. Care must be exercised because of the ease of oxidation of ferrocene to the ferricinium cation. Thus ferrocene cannot be nitrated, chlorinated, or brominated. Acetylation under a variety of conditions (63) has been successful, however. Under intensive Friedel-Crafts conditions further acetylation of acetylferrocene took place exclusively... 

However, in contrast to benzene, ferrocene is sensitive to oxidation, and the ferrocenium cation, FeCpj, a paramagnetic 17-electron species, is readily formed in the presence of various oxidants. The ferrocenium cation is reluctant to undergo electrophilic substitution, and therefore reactions such as halogenation and nitration, which are important routes to substituted benzene derivatives, cannot be used for the synthesis of substituted ferrocenes. Only electrophilic substitution under nonoxidizing conditions (e.g., Friedel-Crafts acylation, Mannich reaction, borylation, lithiation or mercuration), and radical substitution are available as an entry into the chemistry of substituted ferrocenes. 

Favorskil rearrangement of 2-chloro-cyclohexanone, 39, 37 Ferric chloride, 36, 31 37, 77 Ferric nitrate hydrate, 39, 73 Ferrocene, 36, 31, 34 Ferrous chloride solution in tetrahy-drofuran, 36, 31, 34 Fischer indole synthesis, of 1,2-benzo-3,4-dihydrocarbazole, 30, 91 of 1,2,3,4-tetrahydrocarbazole, 30, 90 Flavone, 32, 72 Flavylium chloride, 32, 75 Flow meter, 34, 7 Fluorene, 34, 32 39, 44 Fluorene, 9-methyl-, 39, 43 9-Fluorenecarboxylic acid, 33, 37 o-Fluorobromobenzene, 39, 75... 

---