Photochemistry of [(η-C₅H₅)Fe(η-p-xyl)]PF₆ in Acetonitrile Solution. Characterization and Reactivity of [(η-C₅H₅)Fe(CH₃CN)₃]⁺

The photolysis of [(η-C₅H₅)Fe(η-p-xyl)]⁺ (xyl = xylene) in acetonitrile solution at -40 °C produces a purple intermediate that we have characterized as [(η-C₅H₅)Fe(CH₃CN)₃]⁺ by ¹H NMR, electronic spectroscopy, and chemical reaction studies. Room-temperature photolysis of [(η-C₅H₅)Fe(η-p-xyl)]⁺ in acetonitrile also generates this species, which rapidly yields ferrocene and Fe(II) as the final products. Mechanistic studies on this system suggest that ferrocene is generated when [(η-C₅H₅)Fe(CH₃CN)₃]⁺ releases C₅H₅ ^-, which subsequently replaces three CH₃CN molecules on an unreacted [(η-C₅H₅)Fe(CH₃CN)₃]⁺ ion. This tris(acetonitrile) complex is a convenient starting material for the synthesis of substituted complexes of the form [(η-C₅H₅)Fe(CH₃CN)(L)₂]⁺, [(η-C₅H₅)Fe(CH₃CN)(L)(L′)]⁺, [η-C₅H₅)Fe(L)(L′)₂]⁺, and [(η-C₅H₅)Fe(L)(L′)(L”)]⁺, where L, L′, and L” = isocyanides, phosphites, or phosphines. Room-temperature photolysis of [(η-C₅H₅)Fe(η-p-xyl)]+ in CH₃CN in the presence of excess L produces [η-C₅H₅)Fe(CH₃CN)(L)₂]⁺. Photolysis at -40 °C in CH₃CN, followed by the addition of 1 equiv of L and a warm-up step in the presence of excess L′, produces [(η-C₅H₅)Fe(CH₃CN))L)(L′)]+. The reaction of the disubstituted compounds with excess ligand produces complexes of the form [η-C₅H₅)Fe(L′)(L)₂]⁺ and [(η-C₅H₅)Fe(L)(L′)(L″)], respectively. Reactivity comparisons of [(η-C₅H₅)Fe-(CH₃CN)_n (L)_3-n] and [(η-C₅H₅)Ru(CH₃CN)_n(L)_3-n] (n ≠ 0) have also been made. In every case the Fe complex has been found to undergo substitution reactions more readily than the corresponding Ru analogue.