Asymmetric paramagnetic bimetallocenes of nickel and cobalt

Asymmetric paramagnetic bimetallocenes of nickel and cobalt
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镍和钴的不对称顺磁性双茂金属

DOI：
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
F. Köhler
F. Köhler
中科院分区：
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文献类型：
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作者：
H. Hilbig;F. Köhler

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反应 四甲基五富瓦烯二价阴离子（2）与（C_5Me_5）Ni（acac）（acac =乙酰丙酮根）反应，得到不对称的 十四甲基二茂镍Ni′Ni″（M′和M″ =分别为五-和九甲基噻吩基）。当（C5 Me 5）Co（acac） Co′-C5 Me 4，由（C5 Me 5）Co片段稳定的四甲基五富瓦烯， 得出同样的反应，然后立即用一当量的[Cp 2Fe]+[PF 6]−氧化， 两当量的AgNO 3分别得到十四甲基双钴茂单阳离子和双阳离子Co′Co″+和Co′+Co″+。 通过首先合成五甲基二茂镍， 其与四甲基环戊二烯（Ni′-C5 Me 4 H）偶联。当它去质子化后， 预期的阴离子Ni′-[C5 Me 4]−重排为Ni″-[C5 H4]−。分子轨道计算表明，重排发生通过 [（C5 Me 5）Ni]+片段从2的非甲基化部分向四甲基化部分的移位。反应 Ni″-[C5H4]− 与（C5 Me 5）Co（acac）反应生成混合金属化合物Co′Ni″，Ni′Ni″和Co′Ni″分别有4个和3个未成对电子。它们通过温度依赖性 1H NMR光谱以反铁磁耦合;数据拟合产生J = -195和-174 cm-1。 所有顺磁性化合物均产生强烈位移的1H和13 C NMR信号。实验位移被转换为接触位移，反映了分子内的自旋分布。自旋密度被证明是离域从一个给定的顺磁性茂金属相邻的茂金属，无论它是否是反磁性 或顺磁性的。在后一种情况下，这导致反铁磁耦合。分析了自旋分布 通过MO计算。循环 伏安法显示Co′+Co″+、Ni′Ni″和Co′Ni″进行电子转移，引入多达一个负电荷 和四个正电荷氧化还原电位主要取决于甲基化和电荷定位。
Reaction of tetramethylpentafulvalene dianion (2) with (C5Me5)Ni(acac) (acac = acetylacetonate) gave the asymmetric tetradecamethylbinickelocene Ni′Ni″ (M′ and M″  = penta- and nonamethylmetallocenyl, respectively). When (C5Me5)Co(acac) was used in the reaction, Co′-C5Me4, a tetramethylpentafulvalene stabilized by a (C5Me5)Co fragment, was obtained. The same reaction, followed immediately by oxidation with one equivalent of [Cp2Fe]+[PF6]− and two equivalents of AgNO3, gave the tetradecamethylbicobaltocenium mono- and dications, Co′Co″+ and Co′+Co″+, respectively. Two different metals were introduced in a tetradecamethylbimetallocene by first synthesizing a pentamethylnickelocene, which was coupled to a tetramethylcyclopentadiene (Ni′-C5Me4H). When this was deprotonated, the expected anion Ni′-[C5Me4]− rearranged to Ni″-[C5H4]−. MO calculations demonstrate that the rearrangement occurs through the shift of a [(C5Me5)Ni]+ fragment from the non-methylated to the tetramethylated part of 2. Reaction of Ni″-[C5H4]− with (C5Me5)Co(acac) gave the mixed-metal compound Co′Ni″.Ni′Ni″ and Co′Ni″ have four and three unpaired electrons, respectively. They are shown by temperature-dependent 1H NMR spectra to couple antiferromagnetically; data fits yield J  =  −195 and −174 cm−1, respectively. All paramagnetic compounds gave strongly shifted 1H and 13C NMR signals. The experimental shifts were converted to contact shifts that reflect the spin distribution within the molecules. The spin density proved to be delocalized from a given paramagnetic metallocene to the adjacent metallocene, regardless of whether it was diamagnetic or paramagnetic. In the latter case this led to antiferromagnetic coupling. The spin distribution was analyzed by means of MO calculations.Cyclic voltammetry shows Co′+Co″+, Ni′Ni″ and Co′Ni″ to undergo electron transfers that introduce up to one negative and four positive charges. The redox potentials proved to depend mainly on methylation and charge localization.