Mechanisms of the Photoreactions of Cp2Fe2(CO)4 with Phosphines and Chlorocarbons

Article abstract of DOI:10.1021/ja00357a010

Irradiation (λ>500 nm) of Cp2Fe2(CO)4 (Cp = η⁵-C5H5) in the presence of PR3 (R = Ph, O-i-Pr) in cyclohexane solution at room temperature yields a single product, Cp2Fe2(CO)3(PR3).The reaction with PPh3 (366 nm) is inhibited by excess CO.A reaction intermediate was trapped by irradiating Cp2Fe2(CO)4 in the presence of P(O-i-Pr)3 at -78 deg C in ethyl chloride or THF solution.The infrared spectrum of the intermediate has ν(C<*>O) = 1720 cm^-1, and its electronic spectrum does not exhibit a ? ->?* band.The evidence suggests that the intermediate is Cp(CO)2Fe-CO-Fe(CO)(P(O-i-Pr)3)Cp, a molecule in which a single CO bridges the Fe atoms and in which there were no direct Fe-Fe bond.The mechanism of the photoreaction of PR3 with Cp2Fe2(CO)4 is proposed to involve formation of the CO-bridged intermediate Cp2Fe2(CO)4(PR3), followed by loss of CO to give the product Cp2Fe2(CO)3(PR3).The 366-nm photoreaction of Cp2Fe2(CO)4 with CCl4 or CHCl3 to give CpFe(CO)2Cl occurs mainly by a CpFe(CO)2 radical pathway, because the chlorine atom abstraction is not inhibited by 6 atm of CO.