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.
四甲基五
富勒烯二元离子(2)与(C5Me5)Ni(acac)(acac =
乙酰丙酮)反应,得到了不对称的十四甲基联
镍烯 Ni′Ni″(M′和 M″ 分别 = 五甲基和非甲基联
镍烯)。当在反应中使用 (C5Me5)Co(acac) 时,得到了 Co′-C5Me4,一种由 (C5Me5)Co 片段稳定的四甲基五碳烯。同样的反应,紧接着用一个当量的[Cp2Fe]+[PF6]-和两个当量的 AgNO3 进行氧化,得到了十四甲基二
钴硒单阳离子和二阳离子,分别是 Co′Co″+ 和 Co′+Co″+。
通过首先合成五甲基二茂
镍,然后将其与四
甲基环戊二烯(Ni′-C5Me4H)耦合,在十四甲基二茂
镍中引入了两种不同的
金属。当它被去质子化时,预期的阴离子 Ni′-[C5Me4]- 重排为 Ni″-[C5H4]-。MO 计算表明,重排是通过[(C5Me5)Ni]+ 片段从 2 的非甲基化部分转移到四甲基化部分而发生的。Ni″-[C5H4]- 与 (C5Me5)Co(acac) 反应生成混合
金属化合物 Co′Ni″。所有顺磁化合物的 1H 和 13C NMR 信号都发生了强烈偏移。实验偏移被转换为接触偏移,反映了分子内的自旋分布。事实证明,无论顺磁茂
金属是二磁还是顺磁,自旋密度都会从特定的顺磁茂
金属向相邻的茂
金属分散。在后一种情况下,这导致了反
铁磁耦合。循环伏安法显示,Co′+Co″+、Ni′Ni″和 Co′Ni″发生电子转移,最多可引入一个负电荷和四个正电荷。事实证明,氧化还原电位主要取决于甲基化和电荷定位。