Mechanistic Insight Into High-Spin Iron(I)-Catalyzed Butadiene Dimerization

Iron complexes are commonly used in catalysis, but the identity of the active catalyst is often unknown, which prevents a detailed understanding of structure–reactivity relationships for catalyst design. Here we report the isolation and electronic structure determination of a well-defined, low-valent iron complex that is an active catalyst in the synthesis of cis,cis-1,5-cyclooctadiene (COD) from 1,3-butadiene. Spectroscopic and magnetic characterization establishes a high-spin Fe­(I) center, which is supported by DFT studies, where partial metal–ligand antibonding orbital population is proposed to allow for facile ligand exchange during catalysis.