Dabb Serin L, Fletcher Nicholas C
School of Chemistry and Chemical Engineering, Queen's University of Belfast, David Keir Building, Belfast, Northern Ireland BT9 5AG, UK.
Dalton Trans. 2015 Mar 14;44(10):4406-22. doi: 10.1039/c4dt03535f.
In this perspective, we highlight the issue of meridional (mer) and facial (fac) orientation of asymmetrical diimines in tris-chelate transition metal complexes. Diimine ligands have long been the workhorse of coordination chemistry, and whilst there are now good strategies to isolate materials where the inherent metal centered chirality is under almost complete control, and systematic methodologies to isolate heteroleptic complexes, the conceptually simple geometrical isomerism has not been widely investigated. In systems where the two donor atoms are significantly different in terms of the σ-donor and π-accepting ability, the fac isomer is likely to be the thermodynamic product. For the diimine complexes with two trigonal planar nitrogen atoms there is much more subtlety to the system, and external factors such as the solvent, lattice packing and the various steric considerations play a delicate role in determining the observed and isolable product. In this article we discuss the possibilities to control the isomeric ratio in labile systems, consider the opportunities to separate inert complexes and discuss the observed differences in their spectroscopic properties. Finally we report on the ligand orientation in supramolecular systems where facial coordination leads to simple regular structures such as helicates and tetrahedra, but the ability of the ligand system to adopt a mer orientation enables self-assembled structures of considerable beauty and complexity.
从这个角度出发，我们着重探讨三螯合过渡金属配合物中不对称二亚胺的子午线（mer）和面（fac）取向问题。长期以来，二亚胺配体一直是配位化学的主力军，尽管现在已有很好的策略来分离固有金属中心手性几乎完全可控的材料，以及分离异配体配合物的系统方法，但概念上简单的几何异构现象尚未得到广泛研究。在两个供体原子在σ供体和π接受能力方面存在显著差异的体系中，面式异构体可能是热力学产物。对于具有两个三角平面氮原子的二亚胺配合物，该体系更为微妙，溶剂、晶格堆积和各种空间位阻等外部因素在决定观察到的和可分离的产物方面起着微妙的作用。在本文中，我们讨论了在不稳定体系中控制异构体比例的可能性，考虑了分离惰性配合物的机会，并讨论了它们光谱性质中观察到的差异。最后，我们报告了超分子体系中的配体取向，其中面式配位导致简单规则的结构，如螺旋体和四面体，但配体体系采用子午线取向的能力能够形成具有相当美感和复杂性的自组装结构。
