Influence of acetate ion on the formation reactions of organochromium(III) species. A rapid-scan and high-pressure pulse-radiolysis study

Abstract

A UV/VIS rapid-scan technique was employed to study the formation of organochromium(III) species that are characterized by absorbance maxima at 321 and 412 nm. The effect of acetate on this formation reaction was studied, and spectral measurements demonstrated that it is mainly the monomeric chromium(II) acetate species that react with the alkyl radical, no involvement of the dimeric species being found. A high-pressure pulse-radiolysis technique was employed to study the effect of pressure on the formation of such complexes. The observed volumes of activation exhibit a decrease from +5.7 to –7.4 cm³ mol^–1 on increasing the acetate concentration from 0 to 0.27 mol dm^–3. Similar measurements in the presence of phosphate did not indicate any significant effect on the observed volume of activation for the formation of the metal–carbon bond. This difference can be interpreted in terms of the pressure dependence of the dimerization of chromium(II) acetate complexes, which was measured independently and exhibits a reaction volume of +38 ± 4 cm³ mol^–1. It is concluded that the mechanism of the formation of chromium-carbon δ bonds is not affected by anions such as acetate and phosphate.