A series of μ-oxo - bis[(salen)iron(III)] complexes was prepared from the reaction of the corresponding salen ligands with FeCl 3·6H2O in the presence of NEt3, and characterized by elemental analysis, infrared spectroscopy, and mass spectrometry. These air-stable complexes catalyzed the cyclopropanation of olefins with ethyl diazoacetate in good yields. The catalytic activity of these μ-oxo dimers, in the cyclopropanation of styrene, was examined as a. function of the diamine backbone and the substituents in the 3,3′- and 5,5′-positions of the phenyl rings on the ligands. Solvent variation, catalyst loading, and styrene concentration were investigated to determine the optimal reaction conditions. The complex [Fe(3,3′,5,5′- tBu4salen)]2O (1d) was identified as the most efficient catalyst in the series, which successfully catalyzed the cyclopropanation not only of styrene but also of less reactive substrates such as α-methylstyrene, α-(trifluoromethyl)styrene, 1,1-diphenylethylene, methylenecyclohexane, and n-butyl vinyl ether and internal olefins such as trans- and cis-β-methylstyrene and ethylidenecyclohexane.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry