Remarkable Effects of Axial π* Coordination on the Cr−Cr Quadruple Bond in Dichromium Paddlewheel Complexes
Remarkable Effects of Axial π* Coordination on the Cr−Cr Quadruple Bond in Dichromium Paddlewheel Complexes
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DOI：
10.1021/ja9912675
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发表时间：
1999-07
影响因子：
15
通讯作者：
F. Cotton;L. Daniels;C. A. Murillo;I. Pascual;Hongcai Zhou
中科院分区：
文献类型：
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作者：
F. Cotton;L. Daniels;C. A. Murillo;I. Pascual;Hongcai Zhou
众所周知，在Cr−Cr四重键的σ* 轨道上贡献电子密度会导致Cr−Cr距离的显著延长，并且有一些先前的证据表明，与π* 轨道的配价相互作用会导致类似的延长。现在已经制造了一些分子，允许对这种轴向π* 效应进行明确的评估。分子被设计成确保轴向供给到π* 轨道而不是到σ* 轨道上;已经使用了配体，其中供体原子以这样的方式被束缚到桥连配体，使得它们只能到达π* 轨道而不能到达σ* 轨道。用于此目的的配体是2，6-二（苯基亚氨基）哌啶（DPhIP）和2，2 '-联吡啶胺（dpa）的阴离子。在化合物Cr2（DPhIP）4中，四个亚氨基氮孤对电子被适当地定位以贡献给π* 轨道，并且Cr-Cr键长为2.265（1）A。为了直接比较，合成了化合物Cr2（PhIP）4（PhIP为2-（苯基亚氨基）哌啶的阴离子），并将其与邻苯二甲酰亚胺进行了比较。
It is well-known that donation of electron density into the σ* orbital of a Cr−Cr quadruple bond causes major lengthening of the Cr−Cr distance, and there is some prior evidence that a similar lengthening is caused by dative interaction with the π* orbitals. Some molecules have now been made that allow a definitive assessment of this axial π* effect. A molecule has been designed to ensure that there is axial donation into the π* orbitals but not onto the σ* orbital; ligands have been used in which the donor atoms are tethered to the bridging ligands in such a way that they can reach only the π* orbitals but not the σ* orbital. The ligands used for this purpose are the anions of 2,6-di(phenylimino)piperidine (DPhIP) and 2,2‘-dipyridylamine (dpa). In the compound Cr2(DPhIP)4 four imino nitrogen lone pairs are suitably positioned to donate to the π* orbitals and the Cr−Cr bond length is 2.265(1) A. For direct comparison, the compound Cr2(PhIP)4 (PhIP is the anion of 2-(phenylimino)piperidine) was made and fo...