Pentamethylcyclopentadienyl-rhodium and -iridium complexes. Part XII. Tris(solvent) complexes and complexes of η6-benzene, -naphthalene, -phenanthrene, -indene, -indole, and -fluorene and η5-lndenyl and -indolyl

Abstract

The tris(solvent) complexes [M(C₅H₅)(S)₃][PF₆]₂(M = Rh, Ir; s = Me₂CN, Me₂SO, or pyridine) were prepared and characterised; evidence for less stable solvent complexes (M = Rh, Ir; s = Me₂CO, MeOH, or CH₂Cl₂) was obtained. The dicationic Rh^III and Ir^IIIη⁶-arene complexes [M(C₅Me₅)(arene)][PF₆]₂(M = Rh: arene = benzene, toluene, m-xylene, mesitylene, fluorene, or indole; M = Ir, arene = toluene, m-xylene, naphthalene, phenanthrene, indene, indole, or fluorene) were synthesised from the acetone solvent complexes (IVa; M = Rh)(IVa: M = Ir). Both the naphthalene- and phenanthrene-iridium complexes were very labile, but showed no evidence of fluxional behaviour; phenanthrene is bonded by the terminal 6-membered ring. Reaction of (IVa) with indene gave the η⁵-indenyl complex, [Rh(C₅Me₅)(C₉H₇)][PF₆], which was protonated, with rearrangement, to the η⁵-indene complex. Similar reversible protonation–deprotonation reactions occurred for the iridium complexes, [Ir(C₅Me₅)(η⁶-C₉H₈)]²⁺⇌[Ir(C₅Me₅)(η⁵-C₉H₇)]⁺+ H⁺. The iridium (but not the rhodium)-indole complex [Ir(C₅Me₅)(η⁶-C₈H₆NH)]²⁺ also underwent reversible deprotonation to the η⁵-indolyl complex [Ir(C₅Me₅)(η⁵-C₈H₆N)]⁺. From exchange studies with CF₃CO₂D on [Ir(C₅Me₅)(η⁶-C₇H₈)]²⁺ it is concluded that protonation/deprotonation is fast and that the rate-determming step in the overall reaction is the movement of the metal from the 5- to the 6-membered ring and vice versa. The η⁶-fluorene-rhodium complex is very labile but the iridium analogue is deprotonated by base to give a fluorenyl complex of undetermined structure. An order of stability of η⁵- and η⁶-arenes bonded to Rh^III and Ir^III is given.