The photolysis of chlorocarbonylbis(triphenylphosphine)iridium(I) in chloroform

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Under 254 or 313 nm irradiation in chloroform, [IrCl (CO)(PPh3)2] is converted cleanly to [IrCl2(CO)H(PPh3)2] through the addition of HCl, produced photochemically. Under 254 nm irradiation, some of the reaction of [IrCl(CO)(PPh3)2] occurs by direct photolysis of chloroform, though a greater contribution arises from a reaction initiated through absorption of light by the metal complex. Under 313 nm irradiation, essentially all of the reaction is metal-initiated. The linear dependence of the reaction rate on light intensity and on the fraction of light absorbed by the Ir(I) complex as well as the lack of a deuterium isotope effect rule out a radical process. Instead it is proposed that an association complex between excited state [IrCl(CO)(PPh3)2] and CHCl3 leads to dissociation of a chlorine atom from CHCl3, yielding HCl after abstraction of a hydrogen from another CHCl3. HCl then adds to a ground state [IrCl(CO)(PPh3)2] complex.