An inverted triplesalen ligand by a convergent synthesis and its influence on trinuclear Fe_3~Ⅲ complexes

摘要

The inverted triplesalen ligand H 6 feld Me has been synthesized from 2,4,6-triformyl-phloroglucinol and a ketimine salen half-unit in a convergent synthesis. NMR, IR, and UV-vis spectroscopy reveal that this ligand is not in the O-protonated tautomer but in the N-protonated tautomer with substantial heteroradialene contribution. This ligand and the conventional triplesalen ligand H 6 talen t-Bu 2 have been used to synthesize the trinuclear Fe III complexes [(feld Me )(FeCl) 3 ] and [(talen t-Bu 2 )(FeCl) 3 ], respectively. The molecular structures of these complexes were obtained by single-crystal X-ray diffraction. Two trinuclear Fe III complexes of [(feld Me )(FeCl) 3 ] dimerize via two Fe-phenolate bonds, whereas due to steric hindrance no dimerization is observed for [(talen t-Bu 2 )(FeCl) 3 ]. The structural data also reveal some heteroradialene contribution in the trinuclear complexes. Whereas UV-vis and M bauer spectroscopy are not suitable to distinguish between the two complexes, FT-IR spectra show characteristic features due to the different substitution patterns of the conventional and the inverted triplesalen ligands. Another handle is provided by electrochemistry. Whereas both complexes exhibit an irreversible oxidation wave (0.94 V vs. Fc + /Fc for [(feld Me )(FeCl) 3 ] and 0.84 V vs. Fc + /Fc for [(talen t-Bu 2 )(FeCl) 3 ]), which is assigned to the oxidation of the central backbone, higher potential oxidations are reversible for [(talen t-Bu 2 )(FeCl) 3 ]) but irreversible for [(feld Me )(FeCl) 3 ]. This is attributed to the reversible oxidation of the terminal phenolates in the di-tert-butyl substituted [(talen t-Bu 2 )(FeCl) 3 ] in contrast to the mono-methyl-substituted phenolates in [(feld Me )(FeCl) 3 ]. The magnetic properties of [(talen t-Bu 2 )(FeCl) 3 ] reveal a very small ferromagnetic coupling with significant zero-field splitting of the FeⅢ S = 5/2 ions. In contrast, the dimerization of two trinuclear complexes in [(feld Me )(FeCl) 3 ] results in antiferromagnetic interactions between the two phenolate-bridged Fe III ions, which mask the intra-trinuclear interactions transmitted by the central phloroglucinol backbone.