Ground- and excited-state reactivities of cationic sandwich and half-sandwich complexes of iron(Ⅱ)

摘要

Irradiation of cationic complexes belonging to the [CpFe(η~6-arene)]~+ family (Cp is η~5-C_5H_5) results in the substitution of arene by solvent or other potential ligands present in solution. In solutions containing an epoxide monomer, this photochemical reaction generates a species that initiates polymerization. While several studies of this commercially important process have been reported, the nature of the active initiating species has remained largely conjectural. We have undertaken an investigation that employs two powerful techniques―ion cyclotron resonance Fourier transform mass spectrometry and electrospray ionization mass spectro-metry―to elucidate the mechanism of photoinitiated polymerization in systems containing [CpFe(η~6-arene)]~+ complexes. These techniques have led to the first direct observation of several cationic photoproducts that can serve as initiators for epoxide polymerization. Our results and their mechanistic implications form the subjects of this article.