High-Spin Iron(I) and Iron(0) Dinitrogen Complexes Supported by N-Heterocyclic Carbene Ligands

• Published in: Chemistry : a European journal 2016-09, Vol.22 (40), p.14162-14165
• Main Authors: Ouyang, Zhenwu, Cheng, Jun, Li, Lingling, Bao, Xiaoli, Deng, Liang
• Format: Article
• Language: English
• Subjects: Activation; Carbon; Chemistry; Coordination compounds; Electron spin; Iron; Ligands; Mathematical analysis; Nitrogen compounds; Resonance; Spectroscopy; Stretching; Terminals
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201603390

The use of 1,3‐dicyclohexylimidazol‐2‐ylidene (ICy) as ligand has enabled the preparation of the high‐spin tetrahedral iron(I)‐ and iron(0)–N2 complexes, namely [(ICy)3Fe(N2)][BPh4] (1) and [(ICy)3Fe(N2)] (2), the electronic structures of which have been established by various spectroscopic characterization and DFT calculations. The frequency of the N–N stretching resonance of the iron(0)–N2 complex is the lowest among the reported terminal N2 complexes of iron, signifying the beneficial roles of strongly σ‐donating ligands in combination with the high‐spin low‐valent iron center in promoting N2‐activation. The iron(0)–N2 complex can convert reversibly to the low‐spin iron(II)‐N2 hydride complex [(ICy)2(ICy′)Fe(N2)(H)] (4). The first examples of terminal N2 complexes of high‐spin iron supported by carbon ligands were prepared and structurally characterized. The frequency of the N–N stretching resonance of the iron(0)–N2 complex is the lowest among the reported terminal N2 complexes of iron, signifying the beneficial roles of strongly σ‐donating ligands in combination with the high‐spin low‐valent iron center in promoting N2‐activation (see scheme).