Synthesis and Characterization of Novel Iron(II) Complexes with Tetradentate Bis(N-heterocyclic carbene)-Bis(pyridine) (NCCN) Ligands

Three novel iron(II) complexes bearing tetradentate ligands of the type pyridine–bis(N-heterocyclic carbene)–pyridine (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—in addition to the NCCN ligands—two 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–c, as shown by NMR and IR spectroscopy, as well as by XRD in the case of compound 3c.     «

Three novel iron(II) complexes bearing tetradentate ligands of the type pyridine–bis(N-heterocyclic carbene)–pyridine (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 (N...     »

ISI Document Delivery No.: 929OZ Times Cited: 6 Cited Reference Count: 32 Raba, Andreas Cokoja, Mirza Ewald, Stefan Riener, Korbinian Herdtweck, Eberhardt Poethig, Alexander Herrmann, Wolfgang A. Kuehn, Fritz E. Cokoja, Mirza/B-6906-2009; Kuhn, Fritz/A-3113-2010; Poethig, Alexander/A-9396-2013; Herrmann, Wolfgang/A-3588-2010 EU; Abu Dhabi Petroleum Institute; TUM Graduate School We thank Dr. Osnat Younes-Metzler for valuable help with CV measurements. This work was financially supported by the EU Project Next-GTL. The Abu Dhabi Petroleum Institute and the TUM Graduate School are acknowledged for further financial support. 6 Amer chemical soc Washington     «

ISI Document Delivery No.: 929OZ Times Cited: 6 Cited Reference Count: 32 Raba, Andreas Cokoja, Mirza Ewald, Stefan Riener, Korbinian Herdtweck, Eberhardt Poethig, Alexander Herrmann, Wolfgang A. Kuehn, Fritz E. Cokoja, Mirza/B-6906-2009; Kuhn, Fritz/A-3113-2010; Poethig, Alexander/A-9396-2013; Herrmann, Wolfgang/A-3588-2010 EU; Abu Dhabi Petroleum Institute; TUM Graduate School We thank Dr. Osnat Younes-Metzler for valuable help with CV measurements. This work was financially supported by...     »