Temperature-Induced Spin-Transition in a Low-Spin Cobalt(II) Semiquinonate Complex
Temperature-Induced Spin-Transition in a Low-Spin Cobalt(II) Semiquinonate Complex
复制标题
DOI：
10.1002/anie.200903789
复制
发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Krueger, Hans-Joerg
中科院分区：
文献类型：
--
作者：
Graf, Michele;Wolmershaeuser, Gotthelf;Krueger, Hans-Joerg
自旋交叉和价互变异构是可以作为实现分子开关的基础的过程的例子虽然自旋交叉过程的特征是温度、压力或光诱导金属离子的电子态改变为具有不同自旋多重性的电子态，但价互变异构需要金属离子和配体之间的分子内氧化还原反应，在少数情况下，这伴随着金属离子自旋态的变化各种报道的低自旋钴（III）儿茶酚酸配合物可以通过提高温度转化为高自旋钴（II）半醌酸配合物，为后一过程提供了很好的例子。相比之下，自旋交叉化学主要由带有FeN6配位球的八面体铁（II）配合物主导；然而，已知的含钴（II）的八面体自旋交叉配合物很少本文描述了第一种显示自旋交叉性质而不是价互变异构的半醌酸钴配合物。我们研究的起点是橄榄绿钴（III） 3,5 -二叔丁基儿茶酚酸（dbc2À）配合物[Co-(LN 4Me2)(dbc)]（BPh4）·0.8 MeCN·0.2 Et2O(1))，该配合物含有四氮杂环配体2,11 -双氮[3.3]（2,6）吡啶醌（LN 4Me2）的二甲基衍生物作为配体。用四氟硼酸二茂铁([Fe (Cp) 2]（BF4）氧化红钴（II）儿茶酚酸配合物[Co (ln4me2)(dbc)]（由高氯酸钴（II）、ln4me2和3,5 -二叔丁基儿茶酚酸等摩尔溶液原位制备），产率为42%；Cp=环戊二烯基)，然后与四苯基硼酸钠进行复分解反应（方案1）。根据描述1为儿茶酚酸钴（III）络合物，该物质的溶液和固体具有抗磁性。x射线结构分析1也支持这个分配图1显示了1中复合阳离子的透视图。由于大环的尺寸较小，配体LN 4Me2沿Namine-Namine轴折叠，从而形成扭曲的顺八面体坐标-
Spin crossover and valence tautomerism are examples of processes that can be utilized as a basis for achieving molecular switches.[1] Whereas the spin-crossover process is characterized by a temperature-, pressure-, or light-induced change of the electronic state of the metal ion to one with a different spin multiplicity,[2] valence tautomerism entails an intramolecular redox reaction between a metal ion and a coordinated ligand, which, in a few instances, is accompanied by a change in the spin state of the metal ion.[3] Various reported low-spin cobalt (III) catecholate complexes, which can be transformed into high-spin cobalt (II) semiquinonate complexes by raising the temperature, provide excellent examples of the latter process. In contrast, spin-crossover chemistry is dominated by octahedral iron (II) complexes with a FeN6 coordination sphere;[2] however, there are only very few known octahedral cobalt (II)-containing spin-crossover complexes.[4] Herein we describe the first cobalt (II) semiquinonate complex that displays spin-crossover properties rather than valence tautomerism. The starting point of our investigation was the olive-green cobalt (III) 3, 5-di-tert-butylcatecholate (dbc2À) complex [Co-(LN 4Me2)(dbc)](BPh4)· 0.8 MeCN· 0.2 Et2O (1) containing the dimethyl derivative of the tetraazamacrocyclic ligand 2, 11-diaza [3.3](2, 6) pyridinophane (LN 4Me2) as coligand. This complex was obtained in 42% yield by oxidation of the red cobalt (II) catecholate complex [Co (LN 4Me2)(dbc)](prepared in situ from equimolar solutions of cobalt (II) perchlorate, LN 4Me2, and 3, 5-di-tert-butylcatecholate) with ferrocenium tetrafluoroborate ([Fe (Cp) 2](BF4); Cp= cyclopentadienyl), followed by a metathesis reaction with sodium tetraphenylborate (Scheme 1). In accordance with the description of 1 as a cobalt (III) catecholate complex, solutions and solids of this substance are diamagnetic. X-ray structure analysis of 1 also supports this assignment.[6] Figure 1 shows a perspective view of the complex cation in 1. Because of the small size of the macrocyclic ring, the coordinated ligand LN 4Me2 is folded along the Namine–Namine axis, thereby rendering a distorted cis-octahedral coordina-