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.