Synthesis, structures and catalytic properties of iron(iii) complexes with asymmetric N-capped tripodal NO3 ligands and a pentadentate N2O3 ligand

Abstract

A new family of N-capped tripodal NO(3) proligands N,N-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-N-(2'-hydroxy-5'-R-phenyl)amine [H(3)(L(n))] [when R= Me, n = 1; R= (t)Bu, 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 [H(3)(L(4))] 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 [H(3)(L(5))] with an N(2)O(3) donor set is also reported. Reaction of the proligands [H(3)(L(n))] (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(L(n))(1-Meim)] (n = 1-4) (1-4) respectively, while treatment of the trilithium salt of [H(3)(L(5))] with iron(III) chloride afforded [Fe(L(5))] (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 N(2)O(3) coordination environment. Complex 5 adopts a similar distorted trigonal bipyramidal geometry also with N(2)O(3) coordination around the iron centre. The catalytic activity of these iron complexes towards epoxidation of styrene was examined.