Effect of oxidant on the reaction of [RhCl(cyclooctadiene)(phosphine)] with 1-hexene

Summary A promoting role of an oxidant, present in commercial 1-hexene, in the substitution of phosphine in the complex RhCl(COD)(phosphine)] (1) where the phosphine is PPh₃ or 1/2 BPS-2 bis(diphenylphosphinoethyl)tetra-methyldisiloxane] and COD=cycloocta-1,5-diene, has been detected and explained. When oxidant]>(1)] two reaction steps are distinguished: an oxidation of phosphine to phosphine oxide with generation of RhCl(COD)], followed by its fast dimerization, and an oxidation of the dimer to Rh^III species. When oxidant]<(1)] the latter step is not observed and the reaction of RhCl(COD)] with 1-hexene is favoured, particularly when an excess of phosphine (even at high oxidant concentration) is present. Most rate constants of the individual steps were evaluated.