Attack of molecular iodine to novel palladacyclopentadienyl complexes bearing isocyanides as spectator ligands. A computational and mechanistic study

Abstract

We have synthesized some palladacyclopentadienyl complexes bearing 2,6-dimethylbenzo-, 2-tosylaceto- and t-butyl-isocyanides (DIC, TOSMIC and TIC, respectively) as spectator ligands. The oxidative addition of I2 to the DIC derivatives yielded complexes bearing iodine, the butadienyl fragment σ-coordinated, and the isocyanides in mutual trans position as final species. On the basis of a kinetic study carried out by means of UV–vis and 1H NMR techniques we have proposed a plausible mechanism which is in accord with a computational investigation done by other authors on similar compounds and confirmed by a computational approach we have performed. The proposed mechanism suggests the formation of a Pd(IV) octahedral intermediate complex bearing two iodines in meridional position. The latter yields another intermediate complex bearing iodine, the open butadienyl fragment σ-coordinated, and the isocyanides cis to each other which eventually isomerizes to the final trans product. The reaction rates related to the formation of the cis derivatives (k1) and to the isomerization process (k1′) were determined as refined parameters of the non linear regression analysis of the monoexponential relationship which is a function of the UV–vis spectral changes and time.