Structure, magnetic properties and epoxidation activity of iron(III) salicylaldimine complexes

Abstract

Two new iron(III) complexes with salicylaldimine ligands, [Fe(L¹)Cl]·CH₃CN (1) and [Fe(L²)Cl(H₂O)]·1/3CH₃Cl (2) [H₂L¹ = N,N′-(1,1-dimethylethylene)bis(salicylaldimine), H₂L² = N,N′-(1,1-dimethylethylene)bis(3-methoxysalicylaldimine)], have been prepared and characterized. The X-ray crystal structure analysis shows that the iron(III) ion in complex 1 is in a distorted square pyramidal environment, while in 2, the iron(III) center is six-coordinate with distorted octahedral geometry. The Schiff base ligands L¹ and L² occupied the basal sites, with chloride and water occupying the apical sites. Magnetic susceptibility and Mössbauer effect measurements showed a high-spin configuration (S = 5/2) for Fe(III) in 1 and 2. The temperature dependence of the magnetic data for complexes 1 and 2 is analyzed in terms of the spin-Hamiltonian formalism, which gives an accurate estimate of the zero-field splitting of the ground state of the iron(III) ions as D = 10.2 cm⁻¹ (E = 3.4 cm⁻¹) and D = 7.2 cm⁻¹ (E = 2.4 cm⁻¹, zJ′ = −0.5 cm⁻¹), respectively, in the above two complexes. It has been found for the first time that complexes 1 and 2 activate the epoxidation of cis-stilbene by NaOCl. With 1, the epoxides were produced in 40% yield with cis∶trans = 20∶80, and with 2, the epoxides were produced in 90% yield with cis∶trans = 40∶60.