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.