FeIIPbII and FeIII complexes of macrocyclic compartmental ligands: different cyclization in stepwise template synthesis using FeII/PbII or FeIII/PbII pairs

Abstract

The reaction of [bis(3-formyl-5-methylsalicylidene)ethylenediaminato]iron(II) with diethylenetriamine (dien) in the presence of Pb^II followed by the addition of NaNCS formed a Fe^IIPb^II complex, [FePb(L¹)(NCS)(dmf)(ClO₄)] 1, where (L¹)^2– is a dinucleating macrocyclic compartmental ligand derived from the [2∶1∶1] condensation of 2,6-diformyl-4-methylphenol, ethylenediamine and dien, having “salen”- and “saldien”-like metal-binding sites sharing the phenolic entities. The Fe resides in the “salen” site and the Pb in the “saldien” site: the Fe· · ·Pb intermetallic separation is 3.438(2) Å. The Fe assumes a square-pyramidal geometry with an isothiocyanate nitrogen at the apex. The Pb has a seven-coordinate geometry with a dmf oxygen and a perchlorate oxygen at the axial sites. Complex 1 reacts with molecular dioxygen to give a µ-oxo complex [{FePb(L¹)(NCS)(dmf)(ClO₄)}₂(O)]. A similar reaction of chloro[bis(3-formyl-5-methylsalicylidene)ethylenediaminato]iron(III) with dien in the presence of Pb^II formed a mononuclear Fe^III complex [Fe(H₂L²)(NCS)][ClO₄]₂·dmf 2, where H₂L² is a macrocycle derived from the [2∶2] condensation of 2,6-diformyl-4-methylphenol and dien. The Fe resides in one “saldien” site and assumes an octahedral geometry with an isothiocyanate nitrogen in one apical position. Another metal-binding site formed with dien shows unusual condensation; one primary amino group of the dien condenses with one formyl group to form an usual CN linkage and the remaining primary and secondary amino groups of the dien condense with another formyl group to form a five-membered imidazoline ring.