Title : Structural features of substituted azoles bearing a biologically active heterocycle and their complexes: NMR study
The research work, carried out with the participation of this competition applicant, was devoted to, first of all, the structural analysis of molecular (multi-electron) systems using 1H and 13C nuclear magnetic resonance (NMR) spectra. In a number of cases, other NMR spectra (apart from 1H and 13C) were also employed in the studies. In some works, quantum-chemical calculations were performed. The spatial and electronic structure of various molecules bearing heteroatoms (such as nitrogen, oxygen, sulfur, silicon, and phosphorus) as well as diverse functional groups was investigated. The special research was devoted to the coordination (diamagnetic and paramagnetic) and complex compounds of the donor-acceptor type. Conformational transitions and tautomerism of molecular systems, intramolecular hydrogen bonds, rotational isomerism, competitive coordination, nature of metal–ligand bonds, and mechanisms of chemical transformations were discussed. Almost all studied compounds and their complexes are new (synthesized or isolated from natural feedstock for the first time). Among the investigated compounds there are more than fifty derivatives of the azole series.
1.High-resolution NMR spectra of several dozens of 1-substituted azole derivatives were recorded and analyzed. The values of chemical shifts and spin-spin coupling constants (including those of long-range spin-spin coupling), characteristic of the azole ring and the most well-known functional groups contained in substituted imidazoles and pyrazoles, were determined. It is shown that these parameters can be used to establish the spatial and electronic structure of novel compounds bearing an azole heterocycle.
2.The 1H and 13C NMR spectra of the solutions of 1-vinylimidazole complexes with manganese, cobalt, nickel, and copper chlorides as well as with organylhalostannanes (C2H5)3SnX were analyzed. It is found that in a solution of paramagnetic complexes of 1-vinylimidazole with chlorides of the first transition group elements, the coordinating atom has an octahedral environment, and four ligand molecules occupy the equatorial position. It is established that in the complexes of cobalt, nickel, and copper, 1-vinylimidazole molecules are coordinated to the central ion by the pyridine nitrogen atom N-3. In the paramagnetic complex of manganese, the molecules of this azole can also be coordinated by the pyrrole nitrogen atom N-1 in a certain temperature range. Structurally, the diamagnetic complexes of this azole with organylhalostannanes represent a trigonal bipyramid.
3.A method for the study of molecular structure using the NMR phenomenon in paramagnetic systems has been developed. On the example of 1-substituted azoles, it is shown that this method can be successfully employed to address some issues related to the structure and intramolecular dynamics of multi-electron systems.