Radical cation pathway

There are limitations to the radical cation pathway that need to be considered  

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Scheme 4.102 Cation and radical-cation pathways for selenoglycoside glycosylation.

Surface-catalyzed dark and photoassisted phosphate ester hydrolysis (P—O bond rupture) in aqueous suspensions of TiO2 has been proposed [6,7,41]. A number of products indicative of radical cationic pathways have been reported in the TiO2 photocatalysis of benzyl phosphonic acid [44]. 

Pyridylarenes undergo Cu(II)-catalysed diverse oxidative C-H functionalization reactions. The tolerance of alkene, alkoxy, and aldehyde functionality is a synthetically useful feature of this reaction. A radical-cation pathway (Scheme 4) has been postulated to explain the data from mechanistic studies. A single electron transfer (SET) from the aryl ring to the coordinated Cu(II) leading to the cation-radical intermediate is the rate-limiting step. The lack of reactivity of biphenyl led to the suggestion that the coordination of Cu(II) to the pyridine is necessary for the SET process. The observed ortho selectivity is explained by an intramolecular anion transfer from a nitrogen-bound Cu(I) complex.53... 

Based on this scheme, the kinetics of decomposition of diazodiphenylmethane and diazofluorene in acetonitrile by ZnCl, ZnBr or Znij has been explained Copper complexes of type 416 or 417 have been invoked to account for kinetics and products of the decomposition of diazodiphenylmethane by CuBr in acetonitrile Copper carbenoids of unspecified structure were assumed in analogous investigations with CuBr and CuClO [but not with CufClOJ which initiates a radical cation pathway, vide infra]. Carbenoids 416 (X = Hal) have been isolated from reactions... 

For the interpretation of the Cu-mediated ortho-functionalization of the phenyl residue, a radical cation pathway is invoked. A SET from the phenyl ring to Cu(II) in the N-coordinated species 48 leads to the Cu(I)-coordinated cation-radical intermediate 49, followed by an intramolecular anion transfer in 49 with concomitant decomplexation and deprotonation in an additional SET providing the products (49 50 51). 

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