(η 6-Anisole) (η 2-benzene) dicarbonylchromium(0): an intermediate in the photochemical carbonyl substitution of (η 6-anisole)tricarbonylchromium(0) in benzene

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The photochemical carbonyl substitution of (η 6-anisole)Cr(CO) 3 has been investigated by laser flash photolysis. Both transient spectra and second-order rate constants for the reactions of transients with nucleophiles are found to be extremely variable depending upon solvents used. The coordination of benzene to the transient in cyclohexane forms the transient in benzene, indicating two discrete chemical species: (η 6-anisole)Cr(CO) 2 and (η 6-anisole)Cr(CO) 2(η 2-benzene). The latter type of transient was observed also for fluorobenzene and mesitylene, leading to the assignment of a weak band in the visible region as η 2-arene → Cr charge transfer. The existence of (η 6-arene)Cr(CO) 2(η 2-arene′) may throw light on what have been described as solvent effects in organometallic reactions.