Imidazolium salts decomposition product

The first NHC-AlMes adduct was prepared by Robinson and coworkers in 1996 [133]. Interestingly, a similar adduct, prepared with IfBu in 2010, was found to isomerize in THF or toluene solution to form the abnormal NHC-AlMes adduct coordinated through the C4 position. Decomposition into unknown products was subsequently observed in dichloromethane. Addition of excess trimethylaluminum resulted in the generation of an imidazolium salt with a trinuclear aluminate anion (Scheme 15.12) [134]. 

Thus, the catalyst 7a, highly soluble in imidazolium salt [bmim][X], performed the RCM reaction of A. A -diallyltosylamide at 80°C [46]. The same reaction was performed at room temperature for an 18 h period. After extraction with toluene of the metathesis product, the catalyst could be reused only once due to the slow decomposition of 7a in this medium. 

In comparison with ammonium and pyridinium salts, the thermal decomposition of alkylimidazolium salts is more difficult to predict because of the presence of two nitrogen atoms. Chan et al. [63] have sffidied the isothermal decomposition of 1,3-disubstituted imidazolium iodides in the temperature range 220-260 °C. The presence of alkylimidazoles and alkyl halides was detected in the decomposition products, indicating that the degradation proceeds mainly via a nucleophilic substitution reaction, most likely an Sn2 mechanism (Scheme 2.7). 

Awad et al. [56] reported on the thermal degradation of a series of alkylimidazolium molten salts. Elemental analysis, TGA, and thermal desorption mass spectroscopy (TDMS) were used to characterize the degradation process. A correlation was observed between the chain lengths of the alkyl groups and the thermo-oxidative stability as the chain length increased from propyl, butyl, decyl, hexadecyl, and octadecyl to eicosyl, the stability decreased. Analysis of the decomposition products by FTIR provided information about the decomposition products. It suggested that the thermal decomposition of imidazolium salts followed an SN2 process (Figure 3.12). 

It has been observed that reductive elimination can also occur for aryl-Pd-carbene complexes. Such complexes were investigated in mechanistic studies on Heck coupling and catalyst decomposition routes. Reductive elimination products with direct imidazolium-aryl coupling were observed and in one case fully characterized. Such products provide direct evidence of the Heck coupling mechanism and of intermediates in the catalytic cycle. Important mechanistic studies on the oxidative addition of aryl chlorides to a 14-electron Pd(0)(carbene)2 complex have demonstrated that oxidative addition occurs via a dissociative process and this step is probably the rate-determining step in the amination of aryl chlorides. Aryl-carbene reductive coupling was observed in this study of the amination reaction, and directly coupled aryl-imidazolium compounds were isolated. A further study on an (aryl)Pd(carbene) complex has also demonstrated that such complexes undergo facile reductive elimination to form aryl-imidazolium salt. ... 

Although they have sometimes been regarded as phosphine analogs, NHCs differ from PR in important ways. The thermodynamic instability of ftee NHCs strongly disfavors simple dissociation, but reductive elimination can occur with loss of the imidazolium salt (Eq. 11.48). Many catalysts containing NHCs are nevertheless stable for thousands of turnovers or more, so productive chemistry can be much faster than decomposition via Eq. 11.48. 

It is known that the products of electrochemical decomposition of fluoroborate salts contain fluorinated compounds [12], which are enviroirnientaUy harmful. That is why the azide compound, BMMIiiiNa, is considered as a potentially environmental friendlier electrolyte. The electrochemical reduction of TiCU solutions in BMMImNs IL at 65 °C which is about 20 °C higher than the melting point of the IL has been studied in [8]. This salt was synthesised using the reaction of l-butyl-2,3-dimethyl imidazolium chloride with sodium azide in acetone ... 

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