Cyclopentadienyl- or pentamethylcyclopentadienyl-(arene)cobalt(III) complexes: arene = indole, benzene, mesitylene, hexamethylbenzene, 1,4-dihydroxy- and 1-hydroxy-4-methoxytetramethylbenzene

Abstract

Indole displaces acetone from the complex [Co(C₅Me₅)(OCMe₂)₃][PF₆]₂ to give indole(pentamethylcyclopentadienyl)cobalt(III) hexafluorophosphate in which the cobalt is complexed to the six-membered ring of the indole; attempts to prepare other arene complexes by this procedure have failed. The benzene complex [Co(C₅Me₅)(η-C₆H₆)][BF₄]₂ has been prepared by treatment of [Co(C₅Me₅)(η⁴-C₆H₈)] with [CPh₃][BF₄]. The related complex [Co(C₅H₅)(η-C₆H₆)][BF₄]₂ undergoes arene exchange with mesitylene and hexamethylbenzene to give [Co(C₅H₅)(η-C₆Me_nH_6–n)][BF₄]₂(n= 3 or 6) and with suitable donors (e.g. methyl-substituted benzenes) forms charge-transfer complexes in solution. 2,3,5,6-Tetramethyl-1,4-benzoquinone, C₆Me₄O₂, reacts with [Co(C₅Me₄R)(CO)₂] to give [Co(C₅Me₄R)(η⁴-C₆Me₄O₂)](R = Me or Et). Protonation and methylation of the pentamethylcyclopentadienyl complex gives the 4-hydroxy- and 4-methoxy-2,3,5,6-tetramethyl-1-oxocyclohexadienyl complexes [Co(C₅Me₅){η⁶-C₆Me₄(OR)O}][BF₄](R = H or Me). The latter are converted into the corresponding substituted-benzene complexes [Co(C₅Me₅){η⁶-C₆Me₄(OR)(OH)}]²⁺ by acid. Infrared and ¹H and ¹³C n.m.r. spectra are reported and the relative stabilities of the complexes are discussed.