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.