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Synlett 2015; 26(14): 2047-2048
DOI: 10.1055/s-0034-1381099
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© Georg Thieme Verlag Stuttgart · New York

Ferrocene

Róża Hamera
Department of Organic and Applied Chemistry, University of Łódź, Tamka 12, 94-103 Łódź, Poland   Email: roza.hamera@gmail.com
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Publication History

Publication Date:
10 July 2015 (online)

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Introduction

Ferrocene (1) is an organometallic compound composed of two cyclopentadienyl anions located on both sides of the iron(II) cation. The first report on its synthesis was published in 1951.[1] It was obtained accidentally by Kealy and Pauson, who actually tried to synthetize fulvene by the reaction of (cyclopentadienyl)magnesium bromide with FeCl2 (Scheme [1]). Instead, they isolated an orange coloured solid, which displayed high resistance towards bases and acids. Based on the observed (physico)chemical properties, its structure was determined as a new type of ‘sandwich compounds’.[2] In general, 1 is considered a prototype of metallocenes represented by organometallics, including nickelocene, titanocene, and cobaltocene.[3] In recent years, 1 and its derivatives have attracted great attention as materials with special properties, ligands for asymmetric synthesis, and as important pharmacophores.[4]

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Scheme 1 The first synthesis of ferrocene

Table 1 Use of Ferrocene

Ferrocene (1) was widely applied as a reactive substrate in electrophilic substitution reactions, for example Friedel–Crafts acylation[5a] or alkylation.[5b] Moreover, preparation of (ferrocenyl)diphenylphosphine by a Friedel–Crafts-type reaction of 1 with (chloro)diphenylphosphine was also reported, leading to the formation of a new C–P bond.[5c]

An efficient functionalization of the N-substituted pyrroles by using 1 in the Negishi- or Sonogashira-type coupling reactions was reported.[6a] In addition, application of the Negishi cross-coupling conditions allowed the preparation of diferrocenyl oligopyrroles in satisfactory to good yield.[6b]

Regioselective introduction of a ferrocenyl substituent into 2-phenylindole results in a remarkable increase of cytotoxicity in comparison with the parent compound.[7] Ferrocenyl-substituted indoles inhibit myeloperoxidase activity and were described as promising anti-inflammatory agents.[7]

Triferrocenylsilane was prepared by the ‘salt metathesis’ reaction between ferrocene–lithium and chlorosilane. In addition, the minor product formed in this reaction was identified as diferrocenyl(3,3-dimethylbutyl)silane. The mechanism of the formation of the latter was explained by a cascade of reactions initiated by cleavage and subsequent trapping of a solvent fragment.[8]

Due to the known electron-transfer ability in redox systems, ferrocenyl-substituted compounds are widely applied in electrochemical studies. For example, ferrocenyl containing mono- and biscarbene chromium(0) complexes were synthetized and examined by means of electrochemical methods.[9]

Ferrocene (1) was successfully applied in the Fujiwara−Moritani reaction with (allenyl)methyl ketone in the presence of a catalytic amount of palladium(II) acetate, yielding alkenyl-substituted ferrocenes. Other, functionalized alkenes were also used in analogous reactions with 1. Remarkably, the obtained products displayed (Z)-configuration, exclusively.[10]