Properties of complexes with cobalt–carbon bonds formed by reactions of aliphatic free radicals with nitrilotriacetate–cobalt(II) in aqueous solution. A pulse radiolysis study
The reactions of the aliphatic free radicals ˙R [˙R =˙CH3, ˙CH2OH, ˙CH(CH3)OH, ˙C(CH3)2OH, ˙CH(CH3)OC2H5, ˙CH2CO–2 and CO˙–2] with CoII(nta)(H2O)–2 in aqueous solutions yield the unstable transients (nta)CoIII—R(H2O)– with cobalt–carbon σ bonds. The complexes with ˙R =˙CH3, ˙CH2OH, ˙CH(CH3)OH, ˙C(CH3)2OH and ˙CH(CH3)OC2H5 decompose via homolytic cleavage of the cobalt–carbon bond. The kinetics of reaction of these free radicals with (nta)CoIII—R(H2O)– are reported. The only organic products of the latter reactions are the dimers R—R for ˙R =˙CH3 and ˙CH2OH, whereas a mixture of disproportionation products and dimers is formed for ˙R =˙CH(CH3)OH and ˙C(CH3)2OH. For ˙R =˙CH2OH, ˙CH(CH3)OH and ˙C(CH3)2OH the pKa values for the acidic dissociation of the alcoholic group in the complexes are reported. For ˙R =˙CH2OH the activation parameters for the homolytic dissociation of the cobalt–carbon bond and the acidic dissociation are reported. The ultraviolet–visible spectra of all the transients are reported.