A Process For Preparing A Heterocyclic Carbene Complexes Of The New Method

Since the first free N-heterocyclic carbene was isolated by Ardengo in1991, the studies of N-heterocyclic carbenes and their metal complexes have been intensely developed. Nowadays, N-heterocyclic carbenes and their metal complexes are widely used in the field of homogeneous catalysis, for development of new materials, and syntheses of antibacterial drugs.This dissertational work focuses on a new method for preparation of the N-heterocyclic carbene complexes utilizing alkyl imidazolium salts with BF4-or PF6-known also as commercially available "ionic liquids". Recently, we discovered a straightforward and effective approach to the corresponding N-heterocyclic carbene adducts with BF3and PF5by thermolysis of the related "ionic liquids" under high-vacuum conditions. This process presents a new reaction even analogues of which have never been reported earlier. Unlike in case of imidazolium-based "ionic liquids" with BF4-and PF6-, thermolysis of N-alkylnitrilium tetrafluoroborates affords imidoylfluorides and BF3. This method is also a new one. The only known analogous reaction is the Balz-Schiemann reaction which presents thermolysis of aryldiazonium tetrafluoroborates or hexafluorophosphates and till now is the best synthetic approach to arylfluorides.The present dissertational work comprises four chapters. The first chapter reviews the synthetic approaches to and applications of N-heterocyclic carbenes and their metal complexes.The second chapter presents the Results and Discussion of the data on the in vacuo thermolysis (1Pa,400℃) of1,3-dialkyl-1H-imidazolium salts with BF4-or PF6-which results in formation of (1,3-dialkyl-2,3-dihydro-1H-imidazol-2-ylidene-KC2)trifluoroboron and/or-pentafluorophosphorous and HF. The reaction is not accompanied by any side processes and the typical yields of the products after purification are above94%. Preliminary attempts to prepare carbene adducts with S1F4, SbF5,FeCl3, ZrCI4, and AICI3by the same method resulted by the moment in only a low-yield isolation of an Arduengo carbene adduct with AICl3[trichloro(1,3-dimethyl-2,3-dihydro-1Himidazol-2-ylidene-KC2)aluminium]. All isolated N-heterocy-clic carbene adducts were characterized by NMR spectroscopy on all suitable nuclei and by X-Ray diffraction analysis. The reaction mechanism was modeled by DFT calculations. Thermochemical computations prove the single elementary step mechanism of the reaction and demonstrate that among all possible products the actual ones are the most disfavored by energy and that their formation is possible only due to kinetical reasons.The third chapter reports on our attempt to apply the method for the case of1.2,3-trialkylimidazolium salts with BF4-or PF6-. and1.2.6-trimethylpyridine salt with PF6-. While the reaction was successfully expanded for the case of1,2,3-trimethyl-1H-imidazolium hexafluorophosphate, thermolysis of which affords [(1,3-dimethyl-1H-imidazolium-2-yl) methyl] pentafluorophosphate in a moderate yield, thermolysis of the pyridinium salt proceeds ambiguously.The fourth chapter reports our studies on thermolytic decomposition of N-ethyl substituted acetonitrilium and benznitrilium tetrafluoroborates. At the residual pressure of1Pa and200℃, both nitrilium salts decompose with formation of BF3and correspondent imidoylfluorides. however, with different yields (6and61%, respectively). All compounds were exhaustively characterized by'H,13C{1H}. and19F NMR spectroscopy. For N-ethylated acetonitrile, spin-spin coupling constants with14N quadrupole nucleus were observed in both1H and13C{1H} NMR spectra.