Solvent Effects in Competitive Homolytic and Heterolytic Dediazoniation

Gilbert et al. (1992, see also Galli, 1988) showed that a dual substituent parameter treatment (DSP, see Sec. 7.2) gave the best fit to the influence of substituents as measured by Doyle et al. (1987 a) with Fe(CN)6, as well as for reactions with the ferro complex of ethenediaminetetraacetic acid (Fen-EDTA). 

On the basis of these results it seems to the present author that inner and outer complexes can reasonably be assumed for the electron transfer to the diazonium ion, but that an outer-sphere mechanism is more likely for metal complexes with a completely saturated coordination sphere of relatively high stability, such as Fe(CN) (Bagal et al., 1974) or ferrocene (Doyle et al., 1987 a). Romming and Waerstad (1965) isolated the complex obtained from a Sandmeyer reaction of benzenediazonium ions and [Cu B ]- ions. The X-ray structural data for this complex also indicate an outer-sphere complex. 

Differentiation between inner- and outer-sphere complexes may be possible on the basis of determination of activation volumes of dediazoniations catalyzed by various metal complexes, similar to the differentiation between heterolytic and homolytic dediazoniations in DMSO made by Kuokkanen, 1989 (see Sec. 8.7). If outer-sphere complexes are involved in a dediazoniation, larger (positive) volumes of activation are expected than those for the comparable reactions with inner-sphere complexes. Such investigations have not been made, however, so far as we are aware. 

7 Solvent Effects in Competitive Homolytic and Heterolytic Dediazoniations 

A variety of complex mechanisms operate in thermal dediazoniations of arenediazonium salts leading to a wide range of products. It is useful to summarize some representative results relating to solvolysis products from the literature on this subject (Table 8-1). One recognizes from these data  

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