Ferrocene alkylation

Ferrocene behaves in many respects like an aromatic electron-rich organic compound which is activated toward electrophilic reactions.In Friedel-Crafts type acylation of aromatic compounds with acyl halides, ferrocene is lO times more reactive than benzene and gives yields over 80%. However, ferrocene is different from benzene in respect to reactivity and yields in the Friedel-Crafts alkylation with alkyl halides or olefins. The yields of ferrocene alkylation are often very low. and the separations of the polysubstituted byproducts are tedious. 

Organized multilayers of ferrocene alkyl thiol have been self-assembled on Au(lll) under conditions of controlled thiol concentration. Several methods, such as CV, ellipsometry, STM, AFM, and in situ FTIR spectroscopy have been applied in these studies in order to find out the differences between mono- and multilayers of the same compound [152]. Similar compounds, namely, short-chain alkyl thiols (n = 3-10) with ferrocene terminal group were allowed to form organized monolayers at Au(lll) surfaces [153]. 

Other interesting synthetic applications of the ketone-derived enamine alkylation are found in the monomethylation of steroid enamines (249), extension of the benzylation reaction (250) to a ferrocene derivative (251), the use of a-bromoesters (252) and ketones (252) or their vinylogues (25J), in the syntheses of alantolactone (254-256), isoalantolactone (257), and with a bridged bis-enamine (258). The use of bifunctional alkylating agents is also seen in the introduction of an acetylenic substituent in the synthesis of the characteristic fragrant constituent of jasmine (259), the synthesis of macrocyclic ketolactones (260), the use of butyrolactone (261), and the intermolecular or intramolecular double alkylations of enamines with dihalides (262). 

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. 

Singer and co-workers have investigated the acylation reactions of ferrocene in ionic liquids made from mixtures of [EMIMJI and aluminium(III) chloride (Scheme 6.1-5) [9, 10]. The ionic liquid acts both as solvent and as source of the Friedel-Crafts catalyst. In mildly acidic (X(A1C13) > 0.5 [EMIM]I/A1C13, the monoacetylated ferrocene was obtained as the major product. In strongly acidic [EMIM]I/AlCl3 X(A1C13) = 0.67 the diacylated ferrocene was the major product. Also, when R = alkyl, the diacetylated product was usually the major product, but for R = Ph, the monoacetylated product was favored. 

Formyl- und Acyl-ferrocene werden mit Lithiumalanat/Aluminiumchlorid in glatter Reaktion zu Alkyl-ferrocenen reduziert6 (auch Triphenyl-zinnhydrid in Gegen-wart von Acetylchlorid ist geeignet7). 

CH Alkenylsihines =CH(CH2)nSiR., Rcactivily for Alkylation to Ben/cne (Ferrocene) Other Rodotion... 

Jung etal. reported the Friedel-Crafts type alkylation of ferrocene with allylchlo-rosilancs. The reaction of ferrocene with allylchlorosilanes in the presence of Lewis acid afforded regiospecific alkylated ferrocenes bearing chlorosilyl groups at the /J-carbon to the ferrocene ring (Eq. (4)). 

To optimize the alkylation conditions, ferrocene was reacted with allyldimethyl-chlorosilane (2) in the presence of various Lewis acids such as aluminum halides and Group lO metal chlorides. Saturated hydrocarbons and polychloromethanes such as hexane and methylene chloride or chloroform were used as solvents because of the stability of the compounds in the Lewis acid catalyzed Friedel-Crafts reactions. The results obtained from various reaction conditions are summarized in Table IV. 

As shown in Table IV, the highest catalytic activity of metal halides used as Lewis acid for the alkylation reaction of ferrocene with 2 was observed in methylene chloride solvent. Among Lewis acids such as aluminum chloride, aluminum bromide, and Group 4 transition metal chlorides (TiCl4, ZrCU, HfCU), catalytic efficiency for the alkylation decrea.ses in the following order hafnium chloride > zirconium chloride > aluminum chloride > aluminum bromide. Titanium chloride... 

Ferrocene Bisimidazoline Platinacycle-Catalyzed Intramolecular Friedel-Crafts Alkylations... 

Scheme 1.75 Ferrocene-based sulfur-imine ligands for Pd-catalysed allylic alkylations.

Phosphine ligands based on the ferrocene backbone are very efficient in many palladium-catalyzed reactions, e.g., cross-coupling reactions,248 Heck reaction,249 amination reaction,250 and enantioselective synthesis.251 A particularly interesting example of an unusual coordination mode of the l,l -bis(diphenylphosphino)ferrocene (dppf) ligand has been reported. Dicationic palladium(II) complexes, such as [(dppf)Pd(PPh3)]2+[BF4 ]2, were shown to contain a palladium-iron bond.252,253 Palladium-iron bonds occur also in monocationic methyl and acylpalladium(II) complexes.254 A palladium-iron interaction is favored by bulky alkyl substituents on phosphorus and a lower electron density at palladium. 

In contrast to the problems encountered on photolysis of alkyl- and aryl-sulphonyl azides, we have found that ferrocenylsulphonyl azide 74 is smoothly decomposed by 3500 A light in cyclohexane or in benzene to give ferrocene 15, ferrocenylsulphonamide 16 and the novel bridged [2]ferrocenophanethiazine 1,1-dioxide 17 24>. The yield of 17 varied with the nature of the solvent, being 13.3% in cyclohexane, 67% in benzene, and zero in dimethyl sulphoxide or DMSO/benzene 25>. 

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