Cationic transition-metal complexes. Part II. The reaction of arenes and olefins with bis(cyclo-octa-1,5-diene or norbornadiene)rhodium tetrafluoroborate

Abstract

Treatment of [Rh(nbd)₂]⁺BF₄^– or [Rh(cod)₂]⁺BF₄^–(nbd = norbornadiene, cod = cyclo-octa-1,5-diene) with arenes leads to the displacement of nbd or cod and the formation of [Rh(nbd)(arene)]⁺BF₄^–(arene = C₆Me₆,1,3,5-C₆H₃Me₃, 1,3-C₆H₄Me₂, C₆H₅Me, C₆H₆, C₆H₅OH, or C₆H₅OMe) and [Rh(cod)(arene)]⁺BF₄^–(arene = C₆Me₆, 1,3,5-C₆H₃Me₃, 1,3-C₆H₄Me₂, or C₆H₅Me). Analogous reactions with benzonitrile and aniline gave instead the complexes [Rh(nbd)(C₆H₅CN)₂]⁺BF₄^– and [Rh(nbd)(C₆H₅NH₂)₂]⁺BF₄^–; dimethyl sulphoxide reacts similarly to give [Rh(cod)(Me₂SO)₂]⁺BF₄^–. Reaction of [Rh(C₂H₄)₂(acac)] with Ph₃C⁺BF₄^– and an arene affords [Rh(C₂H₄)₂(arene)]⁺BF₄^–(arene = C₆Me₆, 1,3-C₆H₄Me₂, or C₆H₆).

Bicyclo[2,2,1]heptadiene is dimerised and trimerised catalytically by [Rh(nbd)₂]⁺BF₄^–; the mechanism of this reaction is discussed. Cycloheptatriene (cht) displaces nbd or cod to form [Rh(nbd)(cht)]⁺BF₄^– and [Rh(cod)-(cht)]⁺BF₄^–, which are considered to involve cht bonded in the π(h⁶) form. Cyclohexa-1,3-diene is disproportionated by [Rh(nbd)₂]⁺BF₄^– to cyclohexene and benzene; the 1,4-diene undergoes isomerisation before disproportionation. Sodium benzoate and acetate form bridged carboxylates [Rh(nbd)(rco₂)]₂ on reaction with [Rh(nbd)₂]⁺BF₄^–.