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