Redox Chemistry of Nickel(II)-Complexes Supported by a Series of Non-innocent β-Diketiminate Ligands
Redox Chemistry of Nickel(II)-Complexes Supported by a Series of Non-innocent β-Diketiminate Ligands
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一系列非无害 β-二酮亚胺配体支持的镍 (II) 配合物的氧化还原化学
DOI：
10.1021/ic5006693
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发表时间：
2014
影响因子：
4.6
通讯作者：
and Shinobu Itoh
中科院分区：
文献类型：
--
作者：
June Takaichi;Yuma Morimoto;Kei Ohkubo;Chizu Shimokawa;Takayuki Hojo;Seiji Mori;Haruyasu Asahara;Hideki Sugimoto;Nobutaka Fujieda;Nagatoshi Nishiwaki;Shunichi Fukuzumi;and Shinobu Itoh
合成了一系列β-二酮亚胺配体（RL-，2-取代N-[3-（苯胺基）烯丙基]苯胺衍生物RLH的去质子化形式，R = Me，H，Br，CN，NO2）的镍配合物，并对其结构进行了表征。中性配合物[NiII（RL-）2]被AgSbF 6或[RuIII（bpy）3]（PF 6）3（bpy = 2，2 ′-bipyridine）单电子氧化，得到相应的亚稳态阳离子配合物，其EPR谱为双峰（S= 1/2），在近红外区有特征吸收带，归属于配体间的价间电荷转移（LLIVCT）跃迁. DFT计算表明，镍离子的二价氧化态（Ni Ⅱ）得以保留，而β-双烯酮亚胺配体之一被氧化，形成混合价络合物[Ni Ⅱ（RL-）（RL·）]+。因此，氧化的阳离子络合物的双重自旋状态可以通过考虑高自旋镍（II）离子（S= 1）和支持配体的有机自由基（S= 1/2）之间的反铁磁相互作用来解释。已成功地测定了其中一种阳离子配合物（R = H）的单晶结构，表明阳离子配合物中的两种配体在结构上是等价的。通过对LLIVCT带的理论分析和密度泛函理论计算以及晶体结构的分析，将混合价配合物归属于Robin-Day III类化合物，其中自由基自旋在两个配体之间相等地离域，得到阳离子配合物，其最佳描述为[NiII（RL0.5·-）2]+。当配体上有吸电子取代基（R = CN，NO2，Br）时，配合物与十甲基二茂钴的中性配合物发生单电子还原反应，生成阴离子配合物。生成的阴离子配合物表现出EPR谱由于双峰物种（S= 1/2），但没有显示在近红外区域的LLIVCT带。因此，还原的配合物最好描述为由两个阴离子β-双烯酮亚胺配体[NiI（RL-）2]−支撑的d9镍（I）配合物。这一结论也得到了DFT计算的支持。取代基对三种氧化态（中性，阳离子和阴离子）的配合物的电子结构的影响进行了系统的DFT计算的基础上评估。
Nickel complexes of a series of β-diketiminate ligands (RL–, deprotonated form of 2-substitutedN-[3-(phenylamino)allylidene]aniline derivativesRLH, R = Me, H, Br, CN, and NO2) have been synthesized and structurally characterized. One-electron oxidation of the neutral complexes [NiII(RL–)2] by AgSbF6or [RuIII(bpy)3](PF6)3(bpy = 2,2′-bipyridine) gave the corresponding metastable cationic complexes, which exhibit an EPR spectrum due to a doublet species (S= 1/2) and a characteristic absorption band in near IR region ascribable to a ligand-to-ligand intervalence charge-transfer (LLIVCT) transition. DFT calculations have indicated that the divalent oxidation state of nickel ion (NiII) is retained, whereas one of the β-diketiminate ligands is oxidized to give formally a mixed-valence complex, [NiII(RL–)(RL•)]+. Thus, the doublet spin state of the oxidized cationic complex can be explained by taking account of the antiferromagnetic interaction between the high-spin nickel(II) ion (S= 1) and the organic radical (S= 1/2) of supporting ligand. A single-crystal structure of one of the cationic complexes (R = H) has been successfully determined to show that both ligands in the cationic complex are structurally equivalent. On the basis of theoretical analysis of the LLIVCT band and DFT calculations as well as the crystal structure, the mixed-valence complexes have been assigned to Robin–Day class III species, where the radical spin is equally delocalized between the two ligands to give the cationic complex, which is best described as [NiII(RL0.5•–)2]+. One-electron reduction of the neutral complexes with decamethylcobaltocene gave the anionic complexes when the ligand has the electron-withdrawing substituent (R = CN, NO2, Br). The generated anionic complexes exhibited EPR spectra due to a doublet species (S= 1/2) but showed no LLIVCT band in the near-IR region. Thus, the reduced complexes are best described as the d9nickel(I) complexes supported by two anionic β-diketiminate ligands, [NiI(RL–)2]−. This conclusion was also supported by DFT calculations. Substituent effects on the electronic structures of the three oxidation states (neutral, cationic, and anionic) of the complexes are systematically evaluated on the basis of DFT calculations.