Organic reactions involving transition metals. Part I. Formation of pentamethylcyclopentadienylrhodium complexes by reaction of hexamethylbicyclo[2,2,0]hexa-2,5-diene with rhodium trichloride

Abstract

Reaction of para-bonded hexamethylbenzene, hexamethylbicyclo[2,2,0]hexa-2,5-diene, with rhodium trichloride trihydrate in methanol gives a red solid, also obtained in high yield from the reaction of pentamethylcyclopentadiene with RhCl₃,3H₂O under similar conditions, and now considered to be di-µ-chloro-dichloro(pentamethylcyclopentadienyl)dirhodium(III), (C₅Me₅RhCl₂)₂, rather than the arene complex previously suggested. The same compound has also been obtained in good yields from the reactions of 1-(1-methoxyethyl)-, 1-(1-chloroethyl)- or 1-(1-acetoxyethyl)-pentamethylcyclopenta-2,4-diene and endo-1,2,3,5,6-pentamethyl-4-methylenebicyclo[3,1,0]hex-2-ene with RhCl₃,3H₂O under similar conditions. Evidence is presented that these last reactions and that of hexamethylbicyclo[2,2,0]hexa-2,5-diene occur via a rearrangement to pentamethylcyclopentadiene catalysed by the hydrochloric acid formed in the reaction of methanol with rhodium trichloride. Reaction of the compound (C₅Me₅RhCl₂)₂ with sodium iodide gives the corresponding iodo-complex, (C₅Me₅Rhl₂)₂, and pyridine yields the compound (C₅Me₅)RhCl₂(C₅H₅N).