Synthesis, structures and catalytic properties of iron(iii) complexes with asymmetric N-capped tripodal NO3ligands and a pentadentate N2O3 ligand

Abstract

A new family of N-capped tripodal NO₃ proligands N,N-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-N-(2′-hydroxy-5′-R-phenyl)amine [H₃(Lⁿ)] [when R= Me, n = 1; R= ^tBu, n = 2; R = Cl, n = 3] with different substituents in one of the aryl rings and N,N-bis(2-hydroxy-3-tert-butylbenzyl)-N-(2′-hydroxy-5′-methylphenyl)amine [H₃(L⁴)] were synthesised. The preparation of a new pentadentate proligand N-methyl-N,N′,N′-tris(2-hydroxy-3,5-di-tert-butylbenzyl)ethane-1,2-diamine [H₃(L⁵)] with an N₂O₃ donor set is also reported. Reaction of the proligands [H₃(Lⁿ)] (n = 1–4) with iron(III) chloride in the presence of base (triethylamine) and 1-methylimidazole (1-Meim) as co-ligand led to the formation of iron complexes of the type [Fe(Lⁿ)(1-Meim)] (n = 1–4) (1–4) respectively, while treatment of the trilithium salt of [H₃(L⁵)] with iron(III) chloride afforded [Fe(L⁵)] (5). All complexes were structurally characterised by X-ray crystallography. In complexes 1–4, the ligands form five- and six-membered chelate rings with the iron centres which have distorted trigonal bipyramidal geometry with an N₂O₃ coordination environment. Complex 5 adopts a similar distorted trigonal bipyramidal geometry also with N₂O₃ coordination around the iron centre. The catalytic activity of these iron complexes towards epoxidation of styrene was examined.