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

Abstract

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 Co^II(nta)(H₂O)^–₂ in aqueous solutions yield the unstable transients (nta)Co^III—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)Co^III—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 pK_a 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.