Pentamethylcyclopentadienyl-rhodium and -iridium complexes. Part XI. 1—4-η- and 1,2;5,6-η-Cyclo-octatetraene complexes and their protonation reactions

Abstract

The reaction of [{M(C₅Me₅)Cl₂)}₂](1a; M = Rh) and (1b; M = Ir) with K₂C₈H₈(C₈H₈= cyclo-octatetraene) gave [M(C₅Me₅)(C₈H₈)]. The 1—4-η-C₈H₈ isomers (2) were formed at low temperatures and isomerised to the 1,2:5,6-η-C₈H₈ isomers (3) when warmed in solution. The protonation of co-ordinated cyclo-octatetraene in (2a) and (3a) was investigated using CF₃CO₂H and CF₃CO₂D and was shown to proceed by different paths; (2a) was protonated exo while (3a) was protonated endo to the metal. In both cases two isomers of [Rh(C₅Me₅)(C₈H₉]⁺ were formed, namely (2—6-η-bicyclo[5.1.0]octadienyl)(pentamethylcyclopentadienyl)rhodium, (8a). and (l–3:6,7-η-cyclo-octatrienyl)(pentamethylcyclopentadienyl)rhodium, (9a). Compound (8a) isomerised in solutionto (9a). The protonation of the iridium analogue (2b) gave only (8b). while protonation of (3b) gave a mixture of (8b) and (9b). which did not isomerise.