Mechanistic Studies of Photochemical Reactions with Millisecond Time Resolution by Electrospray Ionization Mass Spectrometry

Electrospray ionization mass spectrometry is used as an on-line technique to investigate the solution photochemistry of [CpFebz]+ (Cp, (eta)5-cyclopentadienyl; bz, (eta)6-benzene). Direct irradiation of samples in the optically transparent tip of the electrospray source allows the detection of products with lifetimes down to the millisecond regime. Photolysis of [CpFebz]+ in acetonitrile (AN) yields the short-lived half-sandwich complex, [CpFe(AN)3]+. The suspected parent-offspring relationship between this species and the fully ring-deligated product, [Fe(AN)6]2+, has been confirmed. In solutions containing cyclohexene oxide, [CpFebz]+ generates several photoproducts capable of initiating the cationic polymerization of the epoxide monomer. The initiation process and the first few steps in the subsequent growth of the polymer chain have been observed.