Insight into the Reactivity of Olefins in the Pauson-Khand Reaction.

The Pauson-Khand reaction of cyclohexene, cyclopentene and norbornene with $μ$-propyne dicobalt hexacarbonyl was studied by DFT and ONIOM calcns. of optimized structures of intermediate cycloalkene complexes and transition states. The calcns. gave the highest barrier (ca. 15 kcal mol-1) and slight endothermicity for reaction of cyclohexene, whereas the barriers for exothermic reactions of cyclopentene and norbornene cycloaddn. are substantially lower (11 and 6 kcal mol-1, resp.). Back donation (cycloalkene-cobalt) was found to be the highest for norbornene by means of CDA calcns. The calcns. at both the DFT and ONIOM levels are concordant with exptl. observations and suggest how the olefin-cobalt interactions in the complex could have a major effect on the relative reactivity of the olefins. [on SciFinder(R)]


Soumis le 12 avril 2018