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 Mossbauer 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 Mossbauer parameters. The products of de- and re-alkylation reactions of the methylthiol complex FeBd2{(MeS)2Gm}(BF)2 have been identified. The correlation of E1/2 values for Fe3+/Fe2+ couples (from cyclic voltammograms) with Hammett σpara constants for substituents in the functionalized fragments is discussed.