Reactions of Ferrocene Derivatives

We can grasp the extent to which the chemistry of the metallocenes has been studied by illustrating only a limited number of typical reactions of various ferrocene derivatives (Figs. 6-2 and 6-3). 

Aminomethylation of ferrocene is significant because of the large number of ferrocene derivatives that can be prepared from the quarternary ammonium salt, some of which are illustrated in Fig. 6-4. 

One of the most interesting reactions of ferrocene derivatives is hetero-anular bridging by the cyclization of a cu-ferrocenyl aliphatic acid, equation (6-11). If = 2, the homoanularly cyclized product is obtained if n = 3 or 4, 

Ferrocenylphenylcarbinyl azide undergoes an acid-catalyzed decomposition to form 1,2-diphenyl-1,2-diferrocenylethane, equation (6-12). 

The cleavage of ferrocene by aluminum chloride in benzene produces 1,1 (-1,3-cyclopentylene) ferrocene [6-12]. PhenyIcyclopentylferrocene is another product of this cleavage [6-13]. 

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RELATIVE REACTIVITIES OF REACTION OF FERROCENE DERIVATIVES WITH MeCOCl... 

Trifan, D. S., and R. Bacskai The role of iron in carbonium ion reactions of ferrocene derivatives. Tetrahedron Letters [London] 1960/13, 1. 

The scope of aminocarbonylations was extended by the works from various groups. For example, Skoda-Fbldes and Kollar studied the carbonylation reactions of ferrocene derivatives in the presence of Pd(OAc)2/PPh3 [126-128]. Ferrocene amides and novel ferrocene a-ketoamides were synthesized in good yields based on palladium-catalyzed aminocarbonylation or double carbonylation of iodofer-rocene at 40-50 bar of CO. The double-carbonylated products were favored at 40-60 °C and amides were produced almost exclusively at 100 °C, as the selectivity of the reaction with less sterically hindered secondary amines is highly dependent on the reaction temperature. Analogous aminocarbonylation reactions of l,l -diiodoferrocene led to I -iodo-ferrocenecarboxamides and I -iodo-ferro-ceneglyoxylic amide-type products. 

There have been further studies of redox reactions of ferrocene derivatives and one-electron oxidation potentials have been... 

As the cyclometalations selectively metalated at the 2-position, it is used for the synthetic reaction of ferrocene derivatives as shown in Scheme 15.1. The representative cyclometalation is called an orthometalation, it is the metalation of a benzene ring at the ortho-position. Metalation at the 2-position of ferrocene corresponds to the orthometalation of the benzene ring. A reaction shown in eq. (15.28) shows the difference of reactivity of a benzene ring and ferrocene ring. 

One of the most useful reactions of ferrocene with regard to synthesizing derivatives is metallation. In this reaction, the lithium derivative is first prepared by the reaction of ferrocene with butyllithium, a reaction showing the slight acidity of the hydrogen atoms. 

Better yields are obtained when polar solvents are utilized and an amine such as tetramethylethyl-enediamine is present, which also facilitates the formation of the dilithium compound. The lithium derivatives undergo a large number of reactions that can be used to produce the enormous number of ferrocene derivatives. Rather than trying to show a great number of reactions, a few of the common reactants and the substituents that they introduce on the cyclopentadienyl rings are shown in Table 21.3. 

While Josiphos 41 also possessed an element of atom-centered chirality in the side chain, Reetz reported a new class of ferrocene-derived diphosphines which had planar chirality only ligands 42 and 43, which have C2- and C -symmetry, respectively.87 Rhodium(i)-complexes of ligands (—)-42 and (—)-43 were used in situ as catalysts (0.75 mol%) for the hydroboration of styrene with catecholborane 1 for 12 h in toluene at — 50 °C. The rhodium/ i-symmetric (—)-43 catalyst system was the more enantioselective of the two - ( -l-phenylethanol was afforded with 52% and 77% ee with diphosphines (—)-42 and (—)-43, respectively. In both cases, the regioselectivity was excellent (>99 1). With the same reaction time but using DME as solvent at lower temperature (—60 °C), the rhodium complex of 43 afforded the alcohol product with an optimum 84% ee. 

In the previous section, we demonstrated the micrometer droplet size dependence of the ET rate across a microdroplet/water interface. Beside ET reactions, interfacial mass transfer (MT) processes are also expected to depend on the droplet size. MT of ions across a polarized liquid/liquid interface have been studied by various electrochemical techniques [9-15,87], However, the techniques are disadvantageous to obtain an inside look at MT across a microspherical liquid/liquid interface, since the shape of the spherical interface varies by the change in an interfacial tension during electrochemical measurements. Direct measurements of single droplets possessing a nonpolarized liquid/liquid interface are necessary to elucidate the interfacial MT processes. On the basis of the laser trapping-electrochemistry technique, we discuss MT processes of ferrocene derivatives (FeCp-X) across a micro-oil-droplet/water interface in detail and demonstrate a droplet size dependence of the MT rate. 

The reaction of ferrocene with butyllithium produces reactive intermediates that can be used to prepare numerous other derivatives ... 

Hartwig reported that the ferrocene-derived phosphines 13,20, and 21 are all effective as supporting hgands in the Pd-catalyzed reaction of aniline derivatives and aryl chlorides, Eq. (107) [72]. These bulky, electron-rich ligands allow for the desired C-N formation to be performed with as httle as 1 mol% Pd. 

Commercially available 1,2 and 1,4 quinones are easily handled. The formal potential of the 1,4-benzoquinone/hydroquinone couple at pH 0 is ca 0.30 V relative to FeCp2. A variety of ferrocene derivatives including l,l -diacetylferrocene have been oxidized by 1,4-benzoquinone in the presence of HBF4, and the ferrocenium salts have been prepared using this reaction [284]. 

Kinetic resolution of ferrocene derivatives, mainly alcohols, had an important place during the early stage of stereochemical investigations of ferrocene derivatives. The reaction of (partially) resolved ferrocenylalkyl alcohols and amines with racemic 2-phenylbutyric acid anhydride (Korean s method) was the basis for the configurational assignment before the establishment of structures by X-ray crystallography [41]. There has been some debate on the reliability of the method [62, 63], and additional chirality information seems necessary for certainty. Recently, the kinetic resolution of 1-ferrocenylethanol by transesterification with vinyl acetate, catalyzed by a lipase from PseudomonasJluorescens, led to an enantiomeric excess of 90—96% of both enantiomers [64], opening new preparative aspects. 

Scheme 5-3. Useful intermediates for the synthesis of ferrocene derivatives containing heteroatoms (a) Lithiation (generally with nBuLi) (b) mercuration with Hg(OAc)2, followed by reaction with LiCl or KCl (c) borylation with B(OnBu)3, followed by hydrolysis (d) CUCI2 (e) CuBr2 (f) compounds containing reactive bromo substituents, e.g., BrCX2 -CX2Br (X = F, Cl) or tosyl bromide (g) A-bromo succinimide (h) I2 (i) Br2.

Any idea of describing each compound that has been prepared must be abandoned. In the following, only the most important types of ferrocene derivatives and reactions are dealt with as for the rest, however. 

As part of a wider study of the chemistry of ferrocene derivatives containing organophosphorus groups, Laguna and co-workers have prepared and structurally characterised ylide complex (57). Other gold complexes containing coordinated ylides reported include mononuclear species (58), (59) and di-nuclear complex (60) which were obtained from the reactions of the ylides or... 

Takahashi and co-workers have performed the living polymerization of ferrocene derivatives to obtain helical, chiral polyisocyanides 183.244 Using 100 equivalents of the monomer and a 20-hour reaction time, polymers with number-average molecular weights ranging between 9800 and 22,000 and PDI = 1.15 were obtained in 90% yield. 

Substituted ferrocenes also form monoanions at very negative potentials electron addition is genuinely associated with the ferrocene nucleus rather than with an electroactive substituent. The E° value for [Fe(f/-C5H4Ph)2] is — 2.62 V, and [FeCp2] itself shows a quasi-reversible reduction at —2.93 V in dmf (452), with a peak separation of 250 mV at — 37°C(v = 1 Vsec-1). Exhaustive electrolytic reduction of ferrocene derivatives yields solutions containing the substituted cyclopentadienide anions the latter may be used in the syntheses of other cyclopentadienylmetal complexes (453). Ferrocenes are also finding use as mediators in electron-transfer reactions, especially at electrode surfaces (454-456). 

Kinetic resolution of ferrocene derivatives, mainly alcohols, had an important place during the early stage of stereochemical investigations of ferrocene derivatives. The reaction of (partially) resolved ferrocenylalkyl alcohols and amines with racemic... 

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