Vinyl-cobalt porphyrins

The incorporation of vitamin B12 derivatives into plasticized poly(vinyl chloride) membranes has resulted in the development of several ion-selective electrodes (ISEs). The response of the electrodes has been related to principles of molecular recognition chemistry. In addition, ISEs have been prepared by electropolymerization of a cobalt porphyrin. These electrodes have selectivity properties that are controlled by both the intrinsic selectivity of the metalloporphyrin and the characteristics of the polymer film (e.g., pore size). 

Recently, Callot and Schaeffer [70] found that cobalt(III) porphyrins react with diazoalkanes to produce substituted vinyl cobalt products in good yield (Eqn. 28). 

Moreover, the reactivation of a cobalt-terminated polymer in the presence of second monomer leads to block copolymerization. In this respect, CMRP has aheady contributed to the preparation of the valuable copolymers listed in Table 4.1. For example, well-defined poly(acrylate) block copolymers were prepared via a sequential polymerization of acrylic monomers with cobalt porphyrin la or cobaloximes 2 [14, 20]. The synthesis of well-defined poly (acrylate)-b-poly(VAc) block copolymers was also achieved with complex la [26]. Co(acac)2 (3a see Figure 4.1) is the most prolific complex for the preparation of block copolymers, until now. Indeed, the sequential CMRP of VAc with NVP [33], AN [48], or vinyl pivalate (VPi) [49] leads to the corresponding block copolymers, in controlled fashion. Throughout the polymerization, the experimental conditions were necessarily adjusted, taking into consideration the reactivity of the second monomer. As an illustration of this, well-defined PVAc-b-poly(acrylonitrile) (PAN) copolymers could only be prepared via a bulk polymerization of VAc at 30 °C, followed by the AN polymerization at 0°C in solution in DMF [48]. In this case, the DMF not only serves as the solvent but also binds the metal and adjusts its reactivity. As a rule, the PVAc sequences of these copolymers were hydrolyzed in order to provide poly(vinyl alcohol) (PVA)-containing derivatives, such as hydrosoluble PVA-b-poly... 

Organo-cobalt Porphyrin Mediated Radical Polymerization of Vinyl Acetate... 

An alternative route used in organometallic chemistry is the reaction of low valent organometallic derivatives with alkyl (aryl) halides. The two electron oxidative addition of alkyl (aryl) halides or cyclopropane derivatives to metalloporphyrins such as [M (Por)] leads to metal alkyl (aryl) o-bonded porphyrins of cobalt " rhodium and iridium ° (Scheme 2). Substitution of aryl and vinyl halides by electrochemically generated iron(I) porphyrins also leads to o-bonded Fe complexes ... 

The cobalt(II) porphyrin complex (CoTPP) has been found to be an efficient catalyst for the Wittig type olefination of acyl phosphonates (96) with ethyl diazoacetate (EDA) in the presence of triphenylphosphine (Seheme 32). ° In a one pot reaction under mild conditions, highly functionalized vinyl phosphonates (97) could be obtained in high yields (72-92%) and high E/Z selectivities (95/5-100/0), in relatively short reaction times. 

Further data have been reported on the reactions of cobalt(m) porphyrins with diazoalkanes as a route to vinyl- or halomethyl-cobalt(m) porphyrin complexes. The reaction pathway, involving probable insertion of an initially generated carbene fragment into the Co—N bond is also discussed. ... 

Kinetic plots for polymerization of vinyl acetate (VAc) initiated by azo radical sources (AIBN and V-70) and mediated by cobalt(ii) tetramesityl porphyrin ((TMP)Co ) in CgDg (Figure 5.16) appear very similar to the corresponding plots for MA polymerization (Figure 5.7). During the induction period radicals that enter solution from the azo radical sources react and are trapped by (TMP)Co as the initially formed organo-cobalt complexes ((TMP)Co-CH(OC(0)CH3)CH3 in a manner that parallel the acrylate... 

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