Synthesis and Characterization of Divalent Manganese, Iron, and Cobalt Complexes in Tripodal Phenolate/N-Heterocyclic Carbene Ligand Environments
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- 作者：Martina K盲脽 ; Johannes Hohenberger ; Mario Adelhardt ; Eva M. Zolnhofer ; Susanne Mossin ; Frank W. Heinemann ; J枚rg Sutter ; Karsten Meyer
- 刊名：Inorganic Chemistry
- 出版年：2014
- 出版时间：March 3, 2014
- 年：2014
- 卷：53
- 期：5
- 页码：2460-2470
- 全文大小：564K
- 年卷期：v.53,no.5(March 3, 2014)
- ISSN：1520-510X
文摘
Two novel tripodal ligands, (BIMPNMes,Ad,Me)鈭?/sup> and (MIMPNMes,Ad,Me)2鈥?/sup>, combining two types of donor atoms, namely, NHC and phenolate donors, were synthesized to complete the series of N-anchored ligands, ranging from chelating species with tris(carbene) to tris(phenolate) chelating arms. The complete ligand series offers a convenient way of tuning the electronic and steric environment around the metal center, thus, allowing for control of the complex鈥檚 reactivity. This series of divalent complexes of Mn, Fe, and Co was synthesized and characterized by 1H NMR, IR, and UV/vis spectroscopy as well as by single-crystal X-ray diffraction studies. Variable-temperature SQUID magnetization measurements in the range from 2 to 300 K confirmed high-spin ground states for all divalent complexes and revealed a trend of increasing zero-field splitting |D| from Mn(II), to Fe(II), to Co(II) complexes. Zero-field 57Fe M枚ssbauer spectroscopy of the Fe(II) complexes 3, 4, 8, and 11 shows isomer shifts 未 that increase gradually as carbenes are substituted for phenolates in the series of ligands. From the single-crystal structure determinations of the complexes, the different steric demand of the ligands is evident. Particularly, the molecular structure of 1鈥攊n which a pyridine molecule is situated next to the Mn鈥揅l bond鈥攁nd those of azide complexes 2, 4, and 6 demonstrate the flexibility of these mixed-ligand derivatives, which, in contrast to the corresponding symmetrical TIMENR ligands, allow for side access of, e.g., organic substrates, to the reactive metal center.