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Tytuł:
Kataliza procesów hydrosililowania z udziałem cieczy jonowych
Catalysis of hydrosilylation processes with the participation of ionic liquids
Autorzy:
Bartlewicz, Olga
Szymańska, Anna
Jankowska-Wajda, Magdalena
Dąbek, Izabela
Maciejewski, Hieronim
Powiązania:
https://bibliotekanauki.pl/articles/1413312.pdf
Data publikacji:
2021
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
hydrosililowanie
kompleksy Rh
kompleksy Pt
ciecze jonowe
SILPC
kataliza heterogeniczna
hydrosilylation
Rh complexes
Pt complexes
ionic liquids
heterogeneous catalysis
Opis:
Hydrosilylation is a fundamental and elegant method for the laboratory and industrial synthesis of organosilicon compounds. The hydrosilylation reaction is usually performed in a single-phase homogeneous system. A major problem, particularly in homogeneous catalysis, is the separation of catalyst from the reaction mixture. The presence of metals in the reaction products, even in trace quantities, is unacceptable for many applications, therefore efforts have been made at applying heterogeneous catalysts or immobilised metal complexes in order to obtain high catalytic activity and easy product isolation at the same time. One of the methods for producing such catalysts is the employment of ionic liquids as agents for the immobilization of metal complexes. Biphasic catalysis in a liquid-liquid system is an ideal approach through which to combine the advantages of both homogeneous and heterogeneous catalysis. The ionic liquids (ILs) generally form the phase in which the catalyst is dissolved and immobilized. In our research we have obtained a number of catalytic systems of such a type which were based on rhodium and platinum complexes dissolved in phosphonium, imidazolium, pyridinium and ammonium liquids. Currently, there has a common trend to obtain heterogenized systems that combine advantages of homogeneous and heterogeneous catalysis, which makes the hydrosilylation process more cost- effective. Such integration of homo- and heterogeneous catalysts is realized in several variants, as supported IL phase catalysts (SILPC) and solid catalysts with ILs layer (SCILL). Although all the above systems show high catalytic activities, their structure is unknown. This is why we have made attempts to modify selected ionic liquids (corresponding to our most effective systems) and we have applied them as ligands in the synthesis of platinum and rhodium complexes. Another group of catalysts comprises anionic complexes of rhodium and platinum which were obtained by reactions between halide complexes of metals and a respective ionic liquid. Most of the obtained complexes are solids insoluble in hydrosilylation reagents and are characterized by a high catalytic activity. A considerable development of heterogeneous catalysts of this type and their application in many hydrosilylation processes can be expected in the future. This mini-review briefly describes the recent progress in the design and development of catalysts based on the presence of ionic liquids and their applications for hydrosilylation processes.
Źródło:
Wiadomości Chemiczne; 2021, 75, 1-2; 5-29
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Asymetryczne przeniesienie wodoru do ketonów katalizowane związkami Rutenu(II) i Rodu(III)
Asymmetric transfer hydrogenation of ketones catalyzed by Ruthenium(II) and Rhodium(III) complexes
Autorzy:
Karczmarska-Wódzka, A.
Kołodziejska, R.
Studzińska, R.
Wróblewski, M.
Powiązania:
https://bibliotekanauki.pl/articles/172550.pdf
Data publikacji:
2012
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
transfer wodoru asymetryczny
związki kompleksowe Ru(II) i Rh(III)
chiralne ligandy
prochiralne związki karbonylowe
asymmetric transfer hydrogenation
Ru(II) and Rh(III) complexes
chiral ligands
prochiral carbonyl compounds
Opis:
Asymmetric hydrogen transfer (ATH) is one of the methods of stereoselective reduction of prochiral carbonyl compounds (Scheme 6). Complexes of the platinum group metals (Noyori catalysts) are the most common catalysts for AT H reactions. The specific structure of the Noyori catalyst allows to activate two hydrogen atoms. These atoms are transferred from donor to acceptor in the form of hydride ion and proton (Scheme 1). Depending on the used catalyst the transfer hydrogenation of ketons can proceed by direct and indirect transfer mechanism. The direct hydride transfer from a donor to an acceptor proceeds via a six-membered transition state (3) (Scheme 2). The indirect hydride transfer proceeds through the formation of an intermediate metal hydride. A monohydride (HLnMH) and or a dihydride (LnMH2) can be formed depending on the catalyst that is used (Scheme 3). In the monohydride route, the reduction proceeds in the inner sphere of the metal (four-membered transition state (4)) or in the outer sphere of the metal (six-membered transition state (5)) (Scheme 4). The proposed reduction of carbonyl compounds in the AT H reaction by Noyori catalysts uses the mechanism of the hydride ion and proton transfer from the donor to the catalyst and the formation of the monohydride. In the indirect transfer hydrogenation the hydride ion and proton are transferred from the monohydride to the acceptor (Scheme 5, 7). AT H reactions that lead to chiral alcohols are conducted in organic solvents or in water. Hydrogen donors most often used in organic solvent reactions are propan-2-ol or an azeotropic mixture of formic acid and triethylamine (Tab. 1, 6). Sodium formate is usually used as hydrogen donor in the reactions conducted in water. Yield and enantioselectivity of the reaction depend on many factors the most important of which are: the structure of a substrate, hydrogen donor and solvent that were used, the reaction time, substrate concentration, and the S/C ratio [2]. In the case of asymmetric reduction conducted in water the solvent pH is also of great importance [3, 7, 8]. An optimal pH range depends on the type of a catalyst [7, 8]. AT H reactions conducted in water are distinguished by a shorter reaction time and higher enantioselectivity than the reactions conducted in organic solvents. In addition, catalysts used in the AT H reactions are more stable in water allowing reuse of the catalyst without loss of its activity. This paper presented examples of the use of specific catalysts in asymmetric reactions of hydrogen transfer. In particular, I drew attention to the reactions running in the aquatic environment due to the above-mentioned advantages of this solvent. The authors focused specifically on bifunctional catalysts based on Ru(II) and Rh(III) on the account of wide usage of the catalysts of that type in AT H reactions in water and their good performance [8, 9, 15, 16, 17, 19, 20, 21, 22]. p-Cymene is the most common aromatic ligand in catalysts based on Ru(II) while in the case of catalysts with Rh(III) the most common is anionic pentamethylcyclopentadienyl ligand. In both cases the second most common ligands are diamines or amino alcohols (Scheme 8). There are better performance and enantioselectivity when diamines are used as ligands. Attempts to replace diamines and amino alcohols by Schiff bases (Scheme 13) in the catalysts containing Rh(III) proved poor results due to a very low enantioselectivity of conducted reactions (Tab. 7).
Źródło:
Wiadomości Chemiczne; 2012, 66, 3-4; 273-295
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-2 z 2

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