Radical addition reactions silver complexes

A review of the photochemical properties of copper complexes includes a survey of the photocatalysed reactions of copper-olefin complexes. The addition of acetonitrile to norbornene may be induced by irradiation in the presence of silver ions. The reaction appears to involve excitation of a LMCT excited state of the norbomene-silver complexes and the formation of norbornene radical cations. 

Cyclopentenes behave differently and often act through radical mechanisms this can lead to photoreduction to cyclopentanes, or photoaddition of the kind exemplified by norborneneand propan-2-ol 12.57). The photoadduct in this process is linked through the carbon atom of the alcohol, and not the oxygen atom. A related addition to acetonitrile 12.58) takes place when norbornene is irradiated in the presence of a silver(i) compound. It is likely thal a metal complex of the alkene is the real irradiation substrate, and the same may be true for copper(i)-promoted additions of haloalkanes to electron-deficient alkenes (2.59). When dichloromelhane is used in such a reaction the product can be reduced electrochemically to a cyclopropane (2.60), which is of value because the related thermal addition of CH.I, to alkenes in the presence of copper does not succeed with electron-poor compounds. 

Reaction (2) illustrates the elegant synthetic potential of the bromo supra-Cp s. In addition, bulky halo- and in particular the bromocyclopen-tadienes are also good sources of long-lived radicals which could react with low-valent metal complexes [Eq. (4)]. The radicals are generated by treatment of the substituted bromo-Cp s with zinc (46) or silver (33). So far, radicals have been only employed once, namely, in the formation of decaphenylnickelocene (78). 

GOase model compounds were lately prepared by Stack and Pratt from two Schiff base derivatives, namely ( )-A A/ -bis(3,5-di- cr -butylsalicylidene)- m s-cyclohexane-l,2-diamine and ( )-AT,A7-bis(3,5-di- cr -butylsalicyl)- m s-cyclohexane-l,2-diamine (H2L ) as shown in Fig. 13 (77). Reaction of Cu(OAc)2 H2O and sodium hydroxide with H2L (Fig- 13a) or H2L (Fig. 13b) in methanol yielded two monocopper complexes, which showed spectroscopic features similar to those of GOase upon oxidation with silver hexafiuoroantimonate. In addition, these two radical compounds could perform the (stoichiometric) oxidation of benzyl alcohol to benzaldehyde, thereby mimicking the oxidizing half-reaction of GOase. 

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