(Indenyl)Iron Complex [(η⁵‐indenyl)Fe(η‐C₆H₆)]⁺: Synthesis, Arene Exchange Reactions and Bonding

The indenyl‐benzene complex [(η⁵‐indenyl)Fe(η‐C₆H₆)]⁺ (2) was synthesized by photochemical reaction of the cyclohexadienyl derivative [(η⁵‐C₆H₇)Fe(η‐C₆H₆)]⁺ and indenyl anion with the subsequent treatment of complex (η⁵‐C₆H₇)Fe(η⁵‐indenyl) formed by acetic acid. Visible light irradiation of cations [(η⁵‐indenyl)Fe(η⁶‐indene)]⁺ (1) or 2 in the presence of substituted benzenes in CH₂Cl₂ results in arene exchange giving [(η⁵‐indenyl)Fe(η⁶‐arene)]⁺ (arene=o‐xylene (3 a), mesitylene (3 b), hexamethylbenzene (3 c) and [2.2]paracyclophane (3 d)). The rate of this reaction is lower than for the related cyclopentadienyl complex [CpFe(η‐C₆H₆)]⁺. μ‐Pentaphospholyl triple‐decker complex [(η⁵‐indenyl)Fe(μ‐η:η‐cyclo‐P₅)FeCp*]⁺ (4) was synthesized by photochemical reaction of 1 with Cp*Fe(η‐cyclo‐P₅). The structures of 2PF₆, 3 cPF₆ and 4PF₆ were determined by X‐ray diffraction. According to energy decomposition analysis, the metal‐benzene bonding in 2 is weaker than in [CpFe(η‐C₆H₆)]⁺ but stronger than in [Cp*Fe(η‐C₆H₆)]⁺. The mechanism of thermal benzene replacement in 2 and [CpFe(η‐C₆H₆)]⁺ as well as structure of excited state were analyzed by DFT calculations.