Vinylferrocene, polymerization

Since the Arimoto/Haven report of vinylferrocene polymerization was not detailed, this monomer was made and both its homopolymerization and its copolymerization were studied with a variety of organic comonomers such as styrene, methylacrylate, maleic anhydride, acrylonitrile, methyl methacrylate, N-vinylpyrolidone, vinyl acetate, and so on.31-38 The polymers were as well characterized as possible, and copolymer compositions were obtained versus feed mole ratios. 

Monomer 61 has a very large steric demand and it is subject to the same internal electron-transfer/termination process discovered earlier for vinylferrocene polymerizations. Only modest molecular weights were achieved and reinitiation sequences were required to get, in our hands, a 31% maximum yield. Copolymerizations with styrene were also successfully performed.90,91... 

Kunitake and coworkers3 first reported the cationic polymerization of vinylferrocene, and Korshak and co-workers33 polymerized 1,1 -diisopropenylferrocene with cationic initiators. Recently,... 

The electrochemical and spectroscopic data indicates that sites on these polymers can communicate with each other, in the electron transfer sense, on a relatively short time scale and without the formation of stable mixed valence clusters. Electronic tranport via hopping or tunnelling and modulated by means of neighboring molecular group collisions would be consistent with these requirements. The relative molecular nonspecificity of this mechanism suggests that other polymeric materials would show similar effects and this has been seen for thin films of poly — (vinylferrocene) and poly — (nitrostyrene). 

Both typical and exceptional examples of the polymerization of a vinyl monomer containing a transition-metal ion are provided by the radical polymerization of vinylferrocene31. Vinylferrocene and its derivatives are polymerized by a radical or a cationic initiator to form a polymer of high molecular weight. The high polymeriz-ability is based on the property that the ferrocene compounds are extraordinarily stable against chemical reactions. 

Electropolyraerization is useful and has been successfully applied to 4-vinylpyridine complexes and to 4-methyl-4 -vinyl-2,2 -bipyridyl.52 Vinylferrocene (vide infra) has been polymerized on to platinum, glassy carbon and titanium dioxide electrodes by introduction to a radiofrequency argon plasma discharge. Electropolymerization and plasma polymerization are likely to be of value to produce copolymers on electrode surfaces. 

Vinylferrocene (22) may be polymerized (Section 57.3.2.2.i) to give a polymer in which the iron(II/III) redox centres are pendant from a carbon backbone. Copolymers have also been formed with styrene61 and acrylonitrile.62 Another approach using a different polymer is illustrated by the covalent binding of poly(methacryl chloride) to Sn02 electrodes followed by attachment of pendant ferrocene centres by reaction of hydroxymethylferrocene.63... 

Addition Polymerization of Vinylferrocenes and Other Vinyl Organometallics... 

Considerable effort in the 1970s by Pittman, George, Hayes, Korshak, and others was applied to exploring the addition polymerization of vinylferrocene 6.1 to give organic polymers with pendent ferrocenyl side groups (6.2 in reaction (l)).1 6 This type of polymerization reaction has been attempted with the use of free radical, cationic, anionic, and Ziegler-Natta methods. 

A number of organometallic polymers containing metallocenes and metallocene analogues has been well-known for some time2. Because of the features of high-temperature stability and radiation resistance of the ferrocene nucleus, ferrocene-containing polymers are of special interest. Basically, these polymers may be divided into two classes the metallocene moiety is either located in a pendant group or in a backbone of the polymer chain. The former polymers have been synthesized by vinyl polymerization of vinyl metallocene monomers such as vinylferrocene. The latter polymers have been prepared by polycondensation of l,l -disubstituted metallocenes or metallocene dihalides with a.w-disubstituted monomers, and fell into two main types, (A) and (B). 

The use of the ETSM to study polymeric systems, especially redox and conducting polymers, is a rapidly growing area of research. It has been used to elucidate die mechanisms of film formation, ion and solvent transport phenmnena, and compositional changes that occur in these films upon redox cycling. Among the redox polymer systems that have been studied are poly(vinylferrocene)... 

Not only polystyrene supports, also other polymer supports were used in the preparation of polymeric amino alcohol ligands for dialkylzinc alkylation. For example, a vinylferrocene derivative with A,N -disubstituted norephedrine was copolymerized with vinylferrocene [60]. This polymeric chiral ligand (53) was used in the ethylation of aldehydes with moderate activity. Brown has reported that chiral oxazaborolidines have catalytic activity in the addition of diethyl zinc to aldehydes [61]. Polymers bearing chiral oxazaborolidines 37 were also active in the reaction and result on moderate enantioselectivity (<58 % ee) [62]. Enantiopure a,a -diphenyl-L-prolinol coupled to a copolymer prepared from 2-hydroxyethylmethacrylate and octadecyl methacrylate... 

It has been reported that vinylferrocene is polymerized by using a radical, cationic, anionic, or Ziegler system initiator [29 — 34]. In particular, higher molecular weight products can be obtained using radical-initiated bulk polymerization [31]. Indeed, both bulk copolymerization and solution copolymerization (in benzene) of 18 with vinylferrocene by using a radical initiator (AIBN) afforded the chiral polymers 19a —e (Scheme 3-13), which were purified by reprecipitation of the benzene solution with methanol. The ratios of the two comonomers were varied in copolymerization. The composition data of the copolymers obtained revealed nearly the same reactivity between 18 and vinylferrocene, which suggests that 19a—e are random copolymers. 

Addition polymerization of ferrocene-containing vinyl monomers is probably the earliest preparation method that has been widely studied. Vinylferrocene 1 [5], the first organometallic monomer, was synthesized in 1955 and its polymerization behavior has been extensively studied under radical [5, 6], cationic [7], and Ziegler-Natta conditions [7] it is inert to anionic initiation [8]. 

The latest vinylferrocene monomer / -C5H4CH202CC(CH3) = CH2 rj -C5H4CH = C(CN)C02Et Fe 15 that undergoes radical polymerization has been prepared as shown in Scheme 10-3 [17] Copolymerization of the monomer with methyl methacrylate produced copolymer 16, via radical initiation using AIBN in benzene. The ethyl a-cyanoacrylate moiety on the ferrocene remained intact through the polymerization process. The thermal behavior of 16 was similar to that of polymethyl methacrylate glass transition temperature, 7 120 °C, melt transition... 

Copolymerization of isopropenylferrocene with styrene, initiated by BF3 OEt2 in CH2CI2 at 0 °C, resulted in the incorporation of styrene when the styrene content of the comonomer feed exceeded 90 wt.% [18]. This result also points to the stable ferrocenyl carbocation acting as an inhibitor in the polymerization. The low level of incorporation of styrene could be attributed to the greater reactivity of the isopropenylferrocene, as also determined for vinylferrocene by Aso and Kunitake, who showed that r for vinylferrocene was greater than that of styrene [20]. 

Researchers turned their attention to applications of silica gel as a new electrode material. Silica gel, which has a three-dimensional structure with high specific surface area and is electroinactive in an aqueous medimn can be used as a support for electroactive species during their formation and/or enzymes by adsorption or entrapment [92,93]. Patel et al. recently reported application of poljwinyl ferrocene immobilized on silica gel particles to construct glucose sensors. Efficiency of carbon paste electrodes prepared with these polymeric electron mediators and GOx was comparable to electrodes constructed with other ferrocene based polymeric electron transfer systems. The fact that 70% of initial anodic current was retained after a month when electrodes were kept in the buffer at room temperature shows that polymerization of monomer vinylferrocene in the pores of silica gel and entrapping GOx in the matrix of poljwinyl ferrocene appears to have added stability to the sensors [94]. 

Daum, P, Lenhard, J.R., Rolison, D., and Murray, R.W. 1980. Diffusional charge transport through ultrathin films of radiofrequency plasma polymerized vinylferrocene at low temperature. Journal of the American Chemical Society 102,4649 653. 

Organometallic polymers, in contrast to coordination polymers, have metal-to-carbon bonds. They are the topic of this chapter. Three seminal events provided the foundation for the field of organometallic polymers to develop. The landmark discovery of ferrocene by Kealy and Pauson in 1951 marked the first organometallic compound.11 This was quickly followed by the full elucidation of its structure and an understanding of its reactivity by Wilkinson, Rosenblum, Whiting, and Woodward.12,13 This history was celebrated in a 2001 feature article in Chemical and Engineering News 4 Finally, the first polymerization of an organometallic compound was reported by Arimoto and Haven at Dupont Co. in 1955.15,16 Vinylferrocene 1... 

Copolymers of 8 and vinylferrocene, containing two different transition metals as shown in 33, were readily prepared by radical addition polymerization. 

The homopolymers of 10 were branched and exhibited broad GPC molecular weight distributions. Studies of the homopolymers molecular weights from polymerization at different monomer concentrations while (1) holding the [10]/[I] ratio constant, and (2) employing different [10]/[I] ratios confirmed that major differences existed in homopolymerizations of 10 versus vinylferrocene.56 In ethylacetate the rate law was r = k [M]1 [I]0 5. Polymerizations in benzene exhibited low initiator efficiencies. The rate was three halves order in the concentration of 10, similar to that found for 8.53 Polymers incorporating 10 were able to catalyze the selective 1,4-hydrogenation of methyl sorbate, but not terminal or internal olefins.56 This resembled the catalytic behavior of styrene/r 6-(styrene)tricarbonylchromium copolymers in hydrogenation.75... 

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