ON THE FLUXIONAL BEHAVIOR OF MONOCOORDINATED DIIMINES AND AZINES
ON THE FLUXIONAL BEHAVIOR OF MONOCOORDINATED DIIMINES AND AZINES
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DOI：
10.1021/ja00252a003
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发表时间：
1987-09-02
影响因子：
15
通讯作者：
VINAIXA, J
中科院分区：
文献类型：
--
作者：
ALVAREZ, S;BERMEJO, MJ;VINAIXA, J
用定性的分子轨道研究方法，分析了双齿双亚胺和氮杂环的单配位配合物中过渡金属中心触变的分子内机理，并讨论了控制这种位移的势垒高度的因素。相关的过程是质子化甲酰胺或三氮杂环化合物中的互变异构，以及主族金属络合物中的触变位移。所有这些体系的一个共同特征是在反应路径上失去了受体轨道和二亚胺的孤子对之间的重叠，而过渡金属络合物的一个独特特征是在孤子对和金属的t2g轨道之一之间出现了四电子排斥。对于八面体配合物，势垒高度的顺序为：Cr<；Mn<；Fe>；Co，反位上α-受体配体的存在有望降低势垒。在配位体方面，氮氮分离和孤对取向是决定势垒高度的主要因素，而与中间碳骨架的轨道混合对势垒的影响较小。根据所提供的轨道分析，氧化还原反应应该允许单齿和双齿化合物的相互转化，而对应于配位场跃迁的波长的光照射应该会对流动过程产生重要的降低势垒。
Intramolecular mechanisms for the haptotropic shift of transition-metal centers in monocoordinate complexes with potentially bidentate diiminesand azines have been analyzed by means of qualitative molecular orbital studies, and the factors controlling the height of the barriers for such shifts are discussed. Related processes are the tautomerism in protonated formamidinates or triazenides, as well as the haptotropic shifts in main group metal complexes. A common feature for all these systems is the loss of overlap between the acceptor orbital and the diimine’s lone pairs along the reaction path, while a unique feature of the transition-metal complexes is the appearance of a four-electron repulsion between the lone pairsand one of the metal’s “t2g” orbitals. For octahedral complexes, the height of the potential energy barrier is expected to be in the order Cr< Mn< Fe> Co, and the presence of a-acceptor ligand in the trans position is expected to lower the barrier. On the ligand side, the nitrogen-nitrogen separation and the lone pair orientation are the main factors determining the height of the barrier, whilemixing with orbitals of the intervening carbon skeleton accounts for smaller changes in thebarrier. According to the orbital analysis presented, redox reactions should allow interconversion of monodentate and bidentate compounds, while irradiation with light of a wavelength corresponding to a ligand field transition should produce an important lowering of the barrier for the fluxional process.