3717-95-1Relevant academic research and scientific papers
Addressing Reversibility of R-NHC Coupling on Palladium: Is Nano-to-Molecular Transition Possible for the Pd/NHC System?
Denisova, Ekaterina A.,Eremin, Dmitry B.,Gordeev, Evgeniy G.,Tsedilin, Andrey M.,Ananikov, Valentine P.
, p. 12218 - 12227 (2019)
It has recently been shown that palladium-catalyzed reactions with N-heterocyclic carbene (NHC) ligands involve R-NHC coupling accompanied by transformation of the molecular catalytic system into the nanoscale catalytic system. An important question appeared in this regard is whether such a change in the catalytic system is irreversible. More specifically, is the reverse nano-to-molecular transformation possible? In view of the paramount significance of this question to the area of catalyst design, we studied the capability of 2-substituted azolium salts to undergo the breakage of C-C bond and exchange substituents on the carbene carbon with corresponding aryl halides in the presence of Pd nanoparticles. The study provides important experimental evidence of possibility of the reversible R-NHC coupling. The observed behavior indicates that the nanosized metal species are capable of reverse transition to molecular species. Such an option, known for phosphine ligands, was previously unexplored for NHC ligands. The present study for the first time demonstrates bidirectional dynamic transitions between the molecular and nanostructured states in Pd/NHC systems. As a unique feature, surprisingly small activation barriers (18 kcal/mol) and noticeable thermodynamic driving force (-5 to -7 kcal/mol) were calculated for C-C bond oxidative addition to Pd(0) centers in the studied system. The first example of NHC-mediated Pd leaching from metal nanoparticles to solution was observed and formation of Pd/NHC complex in solution was detected by ESI-MS.
Microwave assisted synthesis and potent antimicrobial activity of some novel 1,3-dialkyl-2-arylbenzimidazolium salts
Eren, Bilge,Yilmaz, ?zge,?etin, Gül?in,Darcan, Cihan
, p. 621 - 633 (2018/06/06)
Background: Benzimidazolium salts include biologically active benzimidazole ring. Some benzimidazolium salts and their metal complexes, containing different groups, showed remarkable antibacterial, antifungal and antitumor effects. Most of these studies are generally related with the 2-unsubstituted derivatives of benzimidazolium salts which named as N-heterocyclic carbenes (NHCs). To enhance the efficacy of the benzimidazoles in the biological systems, it is very important to overcome the insolubility problem. For this reason and previously indicated structural importance of the benzimidazolium salts, 1,3-dialkyl halide salts of the 2-arylbenzimidazoles, are of focus in this work. To the best of our knowledge, this is the first report that describes the microwave assisted synthesis and antimicrobial activity of 2-arylsubstituted benzimidazolium salts. Methods: A series of novel 1,3-dialkyl-2-arylbenzimidazolium salts (8-28) were synthesized via the N-alkylation of 1-methyl-2-arylbenzimidazole derivatives (1-7) with alkyl halides under microwave conditions by using small amount of DMF. The results were also compared with conventional heating under reflux. Structures of the products were confirmed by using 1H-NMR, 13C-NMR, FTIR spectroscopic techniques. All of the synthesized compounds were screened for their in vitro antimicrobial activities using microbroth tube dilution and disc diffusion methods. Results: Considering the reactions repeated by classical heating, it was determined that the reaction times were decreased from 3-6 hours to 5-35 minutes under microwave. Additionally, yields have increased from 4-71 % to 64-96 % ranges. Considering the whole antimicrobial activity studies, MIC values of newly synthesized benzimidazolium salts 8-28 (1.95->1500 μg/ml) are remarkably smaller than parent benzimidazoles 1-7 (62.5->1500 μg/ml) on the studied microorganisms. Conclusion: The microwave method is advantageous regarding the usage of mild conditions and small amounts of solvent, easy purification and achieving high yields in short times. The antimicrobial activity studies demonstrate that newly synthesized salts (8-28) are effective mostly on grampositives and eukaryotic microorganisms. Compounds 16, 18, 19, 24, 25 and 27 were found to be the most effective inhibitors of growth in both gram-positive bacteria and eukaryotes. Thus, the synthesized compounds in this study may aid the treatment of fungal and bacterial diseases. The results of this study are of great significance in the areas of synthetic organic chemistry, microbiology, pharmaceutical chemistry and chemical catalysis.
