Reactivity of co-ordinated ligands. Part XXII. Protonation of (η-cyclo-octatetraene)(η-cyclopentadienyl)-cobalt(I), -rhodium(I), and -iridium(I)

Abstract

The protonation of (η-cyclo-octatetraene)(η-cyclopentadienyl) complexes [(C₈H₈)M(cp)][(V; M = Co^I, Rh^I, and Ir^I) has been studied. The stable [(C₈H₉M(cp)]⁺ cation, (VI), generated at room temperature has been shown to contain the C₈H₉ moiety co-ordinated to the metal atom via both an η-allyl– and an olefin–metal bond. In the case of M = Co or Rh, a bicyclic cation, (VIa), is produced initially; this subsequently undergoes iso-merisation to a monocyclic form, (VIb). At low temperatures, protonation of the Ir complex yields a metal hydride species [(C₈H₈)IrH(cp)]⁺, (VIII). Mechanisms of proton attack and the ensuing rearrangements are discussed and it is proposed that the proton attacks with endo-stereospecificity.