Fe^IIPb^II and Fe^III complexes of macrocyclic compartmental ligands: Different cyclization in stepwise template synthesis using Fe^II/Pb^II or Fe^III/Pb^II pairs

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 I 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 C=N linkage and the remaining primary and secondary amino groups of the dien condense with another formyl group to form a five-membered imidazoline ring.