Clathrochelate monoribbed-functionalized iron(ii) α-dioximates: synthetic pathways and structural and electrochemical features

Abstract

Monoribbed-functionalized (i.e. functionalization of only one of the three α-dioximate fragments) clathrochelate iron(II) tris-dioximates have been synthesized starting from the dichloride precursor FeBd₂(Cl₂Gm)(BF)₂ (where Bd²⁻ and Cl₂Gm²⁻ are α-benzyldioxime and dichloroglyoxime dianions, respectively), obtained by condensation of the macrocyclic iron(II) bis-α-benzyldioximate [FeBd₂(BF₂)₂(MeCN)₂] with H₂Cl₂Gm. Thioalkyl, alkylamine, oxo- and azaoxocrown ether clathrochelates, as well as the bis-clathrochelate with a 1,5-diaminopentane bridging fragment, have been characterized using elemental analysis, PD mass, IR, UV-vis, ⁵⁷Fe Mössbauer and ¹H, ¹³C and ¹¹B NMR spectroscopies, and X-ray crystallography [for the FeBd₂(Cl₂Gm)(BF)₂·2C₆H₆, FeBd₂{(Et₂N)ClGm}(BF)₂·C₆H₆ and FeBd₂{(MeS)₂Gm}(BF)₂ complexes]. Configurations intermediate between trigonal prismatic and trigonal antiprismatic have been deduced for the low-spin iron(II) ion coordination polyhedra of the monoribbed-functionalized clathrochelates using ⁵⁷Fe Mössbauer parameters. The products of de- and re-alkylation reactions of the methylthiol complex FeBd₂{(MeS)₂Gm}(BF)₂ have been identified. The correlation of E_1/2 values for Fe³⁺/Fe²⁺ couples (from cyclic voltammograms) with Hammett σ_para constants for substituents in the functionalized fragments is discussed.