Elsevier

Polyhedron

Volume 23, Issue 18, 2 December 2004, Pages 3193-3199
Polyhedron

Iron complexes of terdentate nitrogen ligands: formation and X-ray structure of three new dicationic complexes

This work, carried out with Dr. Jacky Kress, Director of Research at the CNRS, who passed away on January 12th, 2003, is dedicated to his memory. We deeply regret our friend and a scientist of great value
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Abstract

Dicationic iron complexes were obtained upon complexation of the ligands 6,6″-di(p-tolyl)-2,2′:6′,2″-terpyridine (L1) or 2,6-bis-(3-mesitylpyrazol-1-yl)pyridine (L2) with iron dichloride or iron trichloride. They were characterized by X-ray diffraction and FT-IR spectroscopy. Single crystal structure determinations of (L1)2Fe2+(FeCl4-)2, (L2)2Fe2+FeCl42- and (L2)2Fe2+(FeCl4-)2(THF)4 all show six-coordinate metal center. These complexes were obtained from L1FeCl2 and L2FeCl2 during recrystallization attempts. (L1)2Fe2+ was shown to be a high-spin complex, whereas (L2)2Fe2+ was shown to be low-spin. For (L2)2Fe2+FeCl42-, two independent dications of very similar geometry but with distinctive distortion were observed by X-ray analysis.

Graphical abstract

The synthesis and X-ray structure of the iron complexes (L1)2Fe2+(FeCl4-)2,(L2)2Fe2+FeCl42-and(L2)2Fe2+(FeCl4-)2(THF)4 (L1 = 6,6″-di(p-tolyl)-2,2′:6′,2″-terpyridine and L2 = 2,6-bis-(3-mesitylpyrazol-1-yl)pyridine) are presented. (L1)2Fe2+ was shown to be a high-spin complex, whereas (L2)2Fe2+ was low-spin.

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Introduction

It has been shown recently that binding 2,6-bis(imino)-pyridyl ligands to iron chlorides leads to five-coordinate complexes that behave as highly efficient catalysts for the polymerization and oligomerization of ethylene, in the presence of a suitable activator [1]. However, subsequent searches for further terdentate ligands inducing similar properties revealed much less positive [2]. In this context, we describe here our studies on the coordination of two N3 donor ligands to iron.

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Results and discussion

The ligand 6,6″-di(p-tolyl)-2,2′:6′,2″-terpyridine (L1, Scheme 1) was best synthesized by a variation of the Kröhnke methodology [3]. Instead of the classical Manich salt, the neutral diamine 2,6-bis(3-dimethylamino-1-oxopropyl-2-ene)pyridine was first obtained in good yield from the reaction of 2,6-diacetylpyridine with two equiv. of N,N-dimethylformamide dimethyl acetal in DMF [4]. It was then reacted with two equiv. of the potassium salt of p-Me-acetophenone in THF, before addition of

General

As the inorganic compounds described herein are air-sensitive, all experiments were performed in a glove box under controlled nitrogen atmosphere. THF, diethyl ether, pentane were dried over Na-benzophenone and acetonitrile over CaH2 before distillation under nitrogen. Anhydrous FeCl2 (Strem) and FeCl3 were used as purchased. Ligand L2 was synthesized according to procedures described previously in the literature [8]. 1H NMR spectra were recorded on Bruker AC-200 or Avance-300 spectrometers at

Supplementary material

Crystallographic data for structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. 203433, 203434, 203435 for (C58H58Cl4Fe2N10) {(L2)2Fe2+FeCl42-}, (C58H46Cl8Fe3N6) {(L1)2Fe2+(FeCl4-)2} and (C74H90Cl8Fe3N10O4) {(L2)2Fe2+(FeCl4-)2(THF)4}, respectively. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road,

Acknowledgements

We are grateful to Mrs. Michelle Martigneaux from the Service Commun NMR and Caroline Dietrich-Schneider from the Service de Spectrométrie de Masse at the University Louis Pasteur Strasbourg.

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