Decacyclene as Complexation Manifold: Synthesis, Structure and Properties of Its Fe2 and Fe4 Slipped Triple-Decker Complexes

• Published in: Chemistry : a European journal Vol. 12; no. 5; pp. 1427 - 1435
• Main Authors: Schneider, Jörg J., Spickermann, Dirk, Lehmann, Christian W., Magull, Jörg, Krüger, Hans-Jörg, Ensling, Jürgen, Gütlich, Philipp
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-02-2006; WILEY‐VCH Verlag
• Subjects: arene ligands; coordination modes; electrochemistry; iron; sandwich complexes
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200500100

Reaction of [(η5‐Me4EtC5)FeIICl(tmeda)] (tmeda=N,N,N′N′‐tetramethylethylenediamine) with a polyanion solution of decacyclene (1) results in the formation of the triple‐deckers [{(η5‐Me4EtC5)Fe}2‐μ2‐(η6:η6‐decacyclene)] (3) and [{(η5‐Me4EtC5)Fe}4‐μ4‐(η6:η6:η6:η6‐decacyclene)] (4). Metal complexation in 3 and 4 occurs on opposite faces of the π perimeter in an alternating mode. The decacyclene ring adopts a gently twisted molecular propeller geometry with twofold crystallographic symmetry (C2). Complex 4 crystallizes in the chiral space group C2221; the investigated crystal only contains decacyclene rings with M chirality. The handedness can be assigned unambiguously to the presence of the iron atoms. Cyclovoltammetric studies revealed quasireversible behavior of the redox events and a strong interaction of the Fe atoms in 3 and 4, exemplified by potential differences ΔE of 660 and 770(780) mV between the first and the second individual oxidation processes. This corresponds to a high degree of metal–metal interaction for 3 and 4. The sucesssful syntheses of 3 and 4 together with earlier results from our laboratory proves that all five‐ and six‐membered π subunit sets of 1 are prone to metal complexation. A clear site preference in 1 towards the complexation of [CpR]iron, ‐cobalt, and ‐nickel fragments exists.
Two out of three naphthalene subunits of decacyclene can coordinate two or four {(η5‐(Me4EtC5)Fe} fragments. These metal–ligand fragments decorate in an alternating fashion different sides of the π perimeter, which adopts a gently twisted propeller geometry (see picture). Cyclic voltammetry revealed a strong electronic interaction of the coordinated iron centers across the decacyclene ligand.