Ferrocene condensation

It was soon discovered that ferrocene condenses with aldehydes under suitable conditions either condensation with elimination of water or carbinol formation may occur 136,166, 202). Further, base-catalyzed aldol and Claisen condensations involving the -hydrogen atom of acetyl-ferrocene can be carried out 100). 

Polysilicone-linked ferrocenes have been synthesized from silyldiolbis(amino-silanyl)ferrocene condensed with a dioP ... 

A different strategy from the above consists in the incorporation of silylamino groups on ferrocene. Condensation of such difunctional reagents with disilanols leads to the formation of polymers where the ferrocene groups are separated by organosilicon spacers [28] (Fig. 8.7). 

Ferrocene condenses with formaldehyde in either concentrated sulfuric acid or liquid hydrogenfluride, followed by reduction, to give a compound containing two ferrocene nuclei and two methylene groups. The compound obtained has been identified as 1,2-diferrocenyl ethane. On the other hand, this condensation using excess ferrocene primarily gives diferrocenylmethane. 

Properties of ferrocene-containing polymers have been improved by inclusion of pyrazole systems in the backbone. The synthesis of (748) was achieved by condensation of bis()3-diketoferrocenes) with aromatic dihydrazines to give polyhydrazones that were later cyclo-dehydrated (B-80MI40408). 

Ferrocene (46.4 g., 0.250 mole) (Note 1) is added to a well-stirred solution of 43.2 g. (0.422 mole) of bis(dimethylamino)-methane (Note 2) and 43.2 g. of phosphoric acid in 400 ml. of acetic acid in a 2-1. three-necked round-bottomed flask equipped with a condenser, a nitrogen inlet, and a mechanical stirrer (Note 3). The resulting suspension is heated on a steam bath under a slow stream of nitrogen (Note 4) for 5 hours (Note 5). The reaction mixture, a dark-amber solution, is allowed to cool to room temperature and is diluted with 550 ml. of water. The unreacted ferrocene is removed by extracting the solution with three 325-ml. jiortions of ether. The aqueous solution is then looled in ice water and made alkaline by the addition of 245 g. 

Hydroxymethylferrocene has been made by condensing ferrocene with N-methylformanilide to give ferrocenecarboxalde-hyde, and reducing the latter with lithium aluminum hydride, sodium borohydride, or formaldehyde and alkali. The present procedure is based on the method of Lindsay and Hauser. A similar procedure has been used to convert gramine methiodide to 3-hydroxymethylindole, and the method could probably be used to prepare other hydroxymethyl aromatic compounds. 

The reaction is carried out under argon in a 2-liter three-necked flask fitted with a mechanical stirrer, reflux condenser, 250-ml pressure-equalizing addition funnel, and gas inlet and outlet. After purging with argon, the flask is charged with a solution of 89 g (0.48 mole) of ferrocene in 1 liter of dry tetrahydrofuran. The solution is next heated to 45°, and there is added dropwise with stirring, 155 ml (0.29 mole) of an -butyllithium solution (15% in heptane-pentane, 2 1, Foote Mineral Co.) during a period of 75 minutes. The resultant solution is maintained at 45° for an additional 2 hours, then is cooled to —77° by means of an external Dry Ice-chloroform bath. 

On the other hand, the yield of ferrocene in a [CpFe(CO)2]2 matrix (50) is not altered up to 80° C, so that here either Cp transfer is not possible or the position on the Fe atom is blocked by CO groups. It seems plausible to consider a rapid ligand condensation as a very early prethermal competitive reaction. One can thus set up a hypothetical reaction scheme such as [using PhHCr(CO)3 as the matrix compound] ... 

We now report a convenient method for the interfacial polycondensation of 1,1 -bis(3-aminoethyl)ferrocene (1) with a variety of diacid chlorides and diisocyanates, leading to ferrocene-containing polyamides and polyureas. In some instances, we have been able to observe film formation at the interface. Moreover, the polymerization reactions can be conveniently conducted at ambient temperatures in contrast to earlier high-temperature organometallic condensation... 

Ferrocene containing condensation polymers have been utilized by us to modify the surfaces of electrodes.Materials of this type that incorporate organo-iron compounds into a polymer matrix, either through chemical bonding or by formation of blends, have the potential of being thermally processed to yield iron oxides. 

One previous synthesis of ferrocene-containing condensation polymers via interfacial methods at room temperature has been reported by Knobloch and Rauscher, who formed low molecular weight polyamides and polyesters by reacting l,l -bis(chloro-formyl)ferrocene with various diamines and diols. Further, Carraher and co-workers have utilized interfacial techniques in the formation of other types of organometallic polymers. 

The condensation reactions described above are unique in yet another sense. The conversion of an amine, a basic residue, to a neutral imide occurs with the simultaneous creation of a carboxylic acid nearby. In one synthetic event, an amine acts as the template and is converted into a structure that is the complement of an amine in size, shape and functionality. In this manner the triacid 15 shows high selectivity toward the parent triamine in binding experiments. Complementarity in binding is self-evident. Cyclodextrins for example, provide a hydrophobic inner surface complementary to structures such as benzenes, adamantanes and ferrocenes having appropriate shapes and sizes 12) (cf. 1). Complementary functionality has been harder to arrange in macrocycles the lone pairs of the oxygens of crown ethers and the 7t-surfaces of the cyclo-phanes are relatively inert13). Catalytically useful functionality such as carboxylic acids and their derivatives are available for the first time within these new molecular clefts. 

The products of condensing substituted benzenes and ferrocene with AI/AICI3 were... 

More recently, recognition of H2PO and ATP2- anions has been observed with dendrimers obtained by condensation of ferrocene-terminated dendrons on octahedral Moe cluster27 (compound 3 in Fig. 6.3) or Au nanoparticles28 cores. 

The reaction of ferrocene and formaldehyde in either concentrated sulfuric acid or liquid hydrogen fluoride, followed by reduction, produces a compound containing two ferrocenyl and two methylene groups (57, 98, 123). After several incorrect assignments had been proposed for the structure of this condensation product, Rinehart and coworkers showed by an unequivocal synthesis that the product was 1,2-diferrocenylethane (XIX) (104). The mechanism of the reaction presumably involves the initial formation of ferrocenylcarbinol (XX) followed by ionization in the strongly acidic medium to the ferrocenylmethyl-carbonium ion (XXI). Conversion to radical ion XXII followed by dimerization and subsequent reduction produces the product. 

Ferrocenecarboxaldehyde and ferrocene also condense to form a deep blue diferrocenylmethine cation. The cation can be isolated in crystalline form as a perchlorate (40). 

A second example of the reactivity of the ferrocene rings is their condensation with formaldehyde and amines (the Mannich condensation) ... 

Ferrocene thus resembles the more reactive thiophene and phenol rather than benzene which does not undergo Mannich condensation. 

In 2001, Sierra and coworkers have reported that ethyl 3-ferrocenylpropanoate reacting with an excess of lithium diisopropylamide (LDA) afforded an enolate that condensed with imine the resulting reaction mixture contained the expected 2-azetidinone as a cisltrans mixture (3 1), and the unexpected 3-hydroxy p-lactam [136]. The ferrocene moiety was linked to the p-lactam ring at the C-3 position, (Scheme 51). 

Condensation polymerization of functional ferrocenes generally yields medium- or low-molecular-weight polymers with broad molecular-weight distributions.12 For example, ferrocenylcarbinol, 6.9, has been condensation-polymerized to polymers 6.10 and 6.11 in the presence of boron trifluoride etherate or zinc chloride (reaction (5)).910 Species 6.11... 

The advantage of these polymers over poly(vinylferrocenes) or related species with pendent organometallic units is that the condensation polymers have ferrocene units in the main chain where they can exert their maximum influence on polymer thermal stability. The disadvantage of the condensation products is that, except in the last example, the molecular weights are too low to favor fiber or flexible film formation. Nevertheless, this work indicated the potential usefulness of polymers with metallocene units in the main chain. 

In other examples, compounds in which a metal atom is already coordinated in a molecule can be used as a comonomer in an addition polymerization. Two examples involve the ferrocenes discussed in Chapter 6. The vinyl ferrocene molecule is shown in 7.14, and a similar vinyl manganese complex in 7.15.30 An alternative approach involves condensation polymerization. For example, if the R group in the ferrocene unit shown in 7.16 contains a hydroxyl group, it can be copolymerized with a diacid chloride. If it is an acid chloride, it can be copolymerized with a diamine. (This type of polymer is called a heteroannular chain if only one of the rings in the repeat unit is in the backbone, the polymer is called homoannular.)7 Similarly, the titanium complex shown in 7.17 is copolymerized with diacids or diols.30 Numerous other examples involving ferrocenes are discussed in Chapter 6. 

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