Kinetics and mechanism of diene exchange at six-co-ordinate chromium

Abstract

The results of kinetic studies on the ligand-exchange and substitution reactions of (buta-1,3-diene) tetracarbonylchromium and tetracarbonyl(trans,trans-hexa-2,4-diene)chromium with cyclo-octa-1,5-diene(cod), norbornadiene (nbd), and P(OR′)₃(R′= Me or Ph) to yield [Cr(cod)(CO)₄], [Cr(nbd)(CO)₄, and [Cr(CO)₄{P(OR′)₃}₂] are consistent with a mechanism involving a stepwise displacement of the diene ligand, which is S_N1 in nature for the diene exchange but contains a ligand-dependent S_N2 component in the case of substitution by phosphite.