Dimerization, oxidative conventional processes

Copolymerizations can proceed in an extraordinary multiplicity of ways. For example, two different monomers may dimerize to a zwitterion or charge transfer complex before the actual polymerization step. Conventional transition states are crossed during the propagation step in the majority of cases but oxidation-reduction processes may also occur. In certain circumstances, the joint polymerization of two different monomers does not lead to copolymers at all, but to polymer mixtures sometimes at all yields and sometimes only when the more reactive monomer is completely, or nearly completely, consumed. 

The evidence is in accord with an addition-elimination mechanism (addition of ArPdX followed by elimination of HPdX) in most cases." In the conventionally accepted reaction mechanism," a four-coordinate aryl-Pd(II) intermediate is formed by oxidative addition of the aryl halide to a Pd(0) complex prior to olefin addition. This suggests that cleavage of the dimeric precursor complex, reduction of Pd , and ligand dissociation combine to give a viable catalytic species." If these processes occur on a time scale comparable to that of the catalytic reaction, nonsteady-state catalysis could occur while the active catalyst is forming, and an... 

The oxidative reactivities of silver(ii) and silver(m) have been compared. The first- and second-order terms in [Ag ] in various reactions have been assessed and an attempt has been made to resolve the apparent reverse of reactivity between the bi-and ter-valent silver ions, depending on the substrate. A reaction scheme for the oxidation of water has been presented and the data are consistent with a reactive dimeric form of Ag. The hydrolysis constant of Ag is also considered to be less than 31 mol . The properties of octaethylporphyrins show the Agi complex to be stable,and cyclic voltammetric studies show reversibility in the +3<- +2 redox steps. In the gold(m) (as AuCl4 ) oxidation of methionine, there is stereospecificity in the reaction, the product being the corresponding sulphoxide with no evidence for a sulphone. The reaction is biphasic, with an initial complex formation which is too rapid for study by conventional techniques followed by a slower intramolecular redox reaction leading to gold(i). The rate of this latter process is dependent on the methionine concentration. The oxidation also takes place when the substrate is part of a peptide chain. 

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