Synthesis and Structures of Cyclopropanedicarboxylate Gallium Complexes

A series of novel gallium dimethylmalonate
and cyclopropane-1,1-dicarboxylate complexes have been synthesized
using gallium halides as Lewis acids. The structure and properties
of the resulting complexes as well as the mechanisms of reactions
involved have been studied. Some complexes have ionic structures and
consist of ligand-bound Ga cations and tetrahalogallate anions. The
structures of gallium complexes were studied by multinuclear NMR spectroscopy,
including that on 71Ga nuclei. Furthermore, X-ray diffraction
analysis was carried out for the six complexes. Dimethyl cyclopropanedicarboxylate
was considered as the simplest analogue of donor–acceptor cyclopropanes.
It is a convenient model for studying such cyclopropanes, while the
complexes obtained are analogues of intermediates in their reactions
catalyzed by Lewis acids. In particular, elongation of the C–CH2 bond in the cyclopropane ring and activation of the latter
by gallium halides have been shown experimentally. The data obtained
are a new step in studies on this very interesting and promising class
of substrates.

以卤化镓作为路易斯酸（Lewis acid），我们合成了一系列新型二甲基丙二酸镓与环丙烷-1,1-二羧酸镓配合物。针对所得到的配合物的结构与性质，以及所涉及反应的反应机理，本研究展开了系统探究。部分配合物具有离子型结构，由配体配位的镓阳离子与四卤合镓阴离子组成。研究人员通过多核核磁共振波谱法（包括针对镓-71原子核的表征）对这类镓配合物的结构进行了分析，此外还对6种该类配合物开展了X射线衍射分析。

环丙烷-1,1-二羧酸二甲酯被视作供体-受体环丙烷（donor–acceptor cyclopropanes）的最简模型底物，是研究此类环丙烷化合物的便捷体系；而本研究中得到的配合物，则是路易斯酸催化下供体-受体环丙烷反应中间体的结构类似物。实验已证实，卤化镓可诱导环丙烷环内C-CH₂键发生伸长，并实现对该环丙烷结构的活化。本研究获取的数据，为这一类极具研究价值与应用前景的底物类别的相关研究提供了新的进展。