Synthesis and Characterization of Novel Iron(II) Complexes with Tetradentate Bis(N-heterocyclic carbene)鈥揃is(pyridine) (NCCN) Ligands
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- 作者：Andreas Raba ; Mirza Cokoja ; Stefan Ewald ; Korbinian Riener ; Eberhardt Herdtweck ; Alexander P枚thig ; Wolfgang A. Herrmann ; Fritz E. K眉hn
- 刊名：Organometallics
- 出版年：2012
- 出版时间：April 9, 2012
- 年：2012
- 卷：31
- 期：7
- 页码：2793-2800
- 全文大小：392K
- 年卷期：v.31,no.7(April 9, 2012)
- ISSN：1520-6041
文摘
Three novel iron(II) complexes bearing tetradentate ligands of the type pyridine鈥揵is(N-heterocyclic carbene)鈥損yridine (NCCN) have been synthesized. The compounds trans-diacetonitrile[bis(o-imidazol-2-ylidenepyridine)alkane]iron(II) hexafluorophosphate (alkane = methane (2a), ethane (2b)) and cis-diacetonitrile[1,3-bis(o-imidazol-2-ylidenepyridine)propane]iron(II) hexafluorophosphate (2c) have been characterized by single-crystal X-ray diffraction (XRD), nuclear magnetic resonance spectroscopy (NMR), and infrared spectroscopy (IR). Cyclic voltammetry (CV) measurements show reversible oxidation of Fe(II) to Fe(III). The rotational barrier of the bridge has been determined via variable-temperature NMR (VT-NMR) studies of 2b. In all complexes, the Fe centers coordinate鈥攊n addition to the NCCN ligands鈥攖wo acetonitrile ligands in the solid state as well as in solution. The alkylene bridge connecting the two NHCs has an influence on the coordination mode of the NCCN ligands. Whereas the methylene- and ethylene-bridged NHC moieties lead to a nearly planar geometry of the NCCN ligand and two trans-positioned acetonitrile ligands, the propylene-bridged complex 2c exhibits a sawhorse-type coordination mode, with two cis-oriented acetonitrile ligands. The reactivity of the synthesized complexes toward substitution of the solvent ligands was investigated, showing that acetonitrile is readily substituted by benzonitrile. Upon addition of carbon monoxide, one acetonitrile ligand is replaced by CO to yield complexes 3a鈥?b>c, as shown by NMR and IR spectroscopy, as well as by XRD in the case of compound 3c.