The thesis is devoted to the search for and development of alternative heterogeneous catalytic systems in conditions of a “palladium crisis,” in particular systems based on pure rhenium sulfide and rhenium sulfide deposited on coal, as well as palladium on coal and other carriers with a reduced mass fraction of palladium to reduce the consumption of metallic palladium in synthetic practice.
A series of catalytic experiments was used to study the kinetics of the hydrogenation process on rhenium sulfide, establish the optimal conditions for hydrogenation, and determine the limits of applicability of this catalyst. The proposed catalytic system based on Re2S7 allowed a series of substituted tetrahydroquinolines, tetrahydroisoquinolines, and thiolans in multigram quantities with the preservation of C-halogen bonds, including bromine and iodine derivatives. For the first time, carboxyl-functionalized tetrahydrothiophene was obtained by direct hydrogenation of thiophene derivatives.
It has been shown that rhenium sulfide cannot replace palladium on charcoal, particularly in reactions involving the removal of benzyl protection, benzoxycarbonyl protection, and in reactions involving the hydrogenation of isolated double bonds. It also does not allow thiolane formation in the presence of unprotected and protected amines— nitrogen atom detachment occurs, followed by catalyst inhibition. This is a serious limitation of the application of Re2S7, but it has the potential to become an important addition to a number of heterogeneous catalysts due to its high tolerance to halogens and sulfur-containing compounds, with the exception of mercaptans.
In the course of the work, a comprehensive physicochemical study of the obtained catalyst based on rhenium sulfide and its composites with activated carbon was carried out. It has been shown that an alternative and effective way to reduce palladium costs is to use nanoscale palladium deposited on activated carbon using thermolysis of 0-valent palladium complexes Pd2(dba)3. In particular, this work presents a method for obtaining 1% by weight palladium composites on commercially available activated carbon and on polyaniline, as well as composites of complex structure Pd/PANI/C.
A physicochemical analysis of the properties of palladium carbon carriers was carried out with regard to their suitability for the synthesis of highly active palladium on carbon samples, and it was established that the main factor related to the carrier that determines the catalytic activity of composites is the size of the carrier pores—a large number of mesopores correlates with the high activity of the obtained catalyst samples. On the other hand, the specific surface area does not have a decisive influence on the catalytic ability. Polyaniline, as a palladium carrier, showed significantly worse results than coal, and in the polyamine/coal composite, it reduced the catalytic activity of palladium, probably due to a decrease in the number of pores available for metal deposition and a change in the chemical nature of the surface.
