The current work reports the judicial selection and subsequent dehydrogenation reaction with ionic liquid (IL) facilitated ethylene diamine bisborane (EDAB). Quantum chemical based COSMO-SAC (COnductor like Screening MOdel Segment Activity Coefficient) model was initially used to screen the ILs as available from Sigma Aldrich. LUMO-HOMO calculation was then performed to analyze the stability of EDAB/IL complexes. The molecular modeling studies converged on the two ILs, namely 1-ethyl-3-methyl imidazolium acetate ([EMIM][OAc]) and 1-butyl-3-methyl imidazolium acetate ([BMIM][OAc]), which were subsequently chosen for the dehydrogenation experiments. The thermal dehydrogenation of EDAB was carried out at 95 C and 105 C under vacuum so as to prevent generation of oxygen moieties. A total of 3.96 and 3.52 equivalents of hydrogen were released from the desorption of EDAB/[BMIM][OAc] and EDAB/[EMIM][OAc], respectively, at 105 C. The purity of released gas was confirmed by gas chromatographic analysis, while the catalytic activity of ILs was confirmed by 1 H NMR characterization of pure EDAB, ILs and EDAB/IL complexes both before and after the reaction. 11 B NMR analysis confirms the presence of trigonal boron (sp 2 ) BH 2 group as the only hydrogen containing boron moiety in dehydrogenated EDAB. Further, the two-stage release mechanism of EDAB was also verified by thermogravimetric analysis. High resolution mass spectrometry was able to detect the mass of cyclic repeat units in the polymeric chain containing an sp 2 BH 2 group. † Electronic supplementary information (ESI) available: The COSMO-SAC parameters and the sigma proles of EDAB, imidazolium cations and acetate anions. Further it also depicts the HOMO-LUMO energy gap of EDAB, [EMIM] [OAc] and [BMIM][OAc]. SeeFig. 8 Plot for 11 B NMR. (a) EDAB/[BMIM][OAc] before reaction, (b) EDAB/[BMIM][OAc] after reaction.This journal is
This work reports the use of allyl-based imidazolium cations for dehydrogenation of ethylene diaminebisborane (EDAB) at three different temperatures, namely, 95, 105, and 115 °C, under vacuum. The allyl-based ionic liquid (IL) was selected by using the infinite dilution activity coefficient (IDAC) as predicted from the COSMO-SAC (COnductor-like Screening MOdel−Segment Activity Coefficient) model. Based on the results of the COSMO-SAC model, the following allylbased ILs were used for experimentation: 1-allyl-3-methylimidazolium dicyanamide ([AMIM][N(CN) 2 ]), 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([AMIM][Tf 2 N]), and 1-allyl-3-methylimidazolium bromide ([AMIM][Br]). The highest amount of hydrogen (3.25 equiv) was measured from the EDAB/[AMIM][Br] system at 115 °C. Gas chromatography was conducted to confirm that the gas released was pure hydrogen. To better understand the reaction mechanism of EDAB dehydrogenation, the Reactive Force Field (ReaxFF) method was employed. Further analyses with 1 H and 11 B NMR were performed on pure IL and IL/EDAB complexes to reassert the role of IL as a catalyst. Thermogravimetric analysis was also conducted on pure EDAB, pure IL, and EDAB/IL complexes to understand the weight loss phenomenon with respect to rising temperature.
This work reports the thermal dehydrogenation of chemical hydrides, namely, ammonia borane (AB) and ethylene diamine bisborane (EDAB), in the presence of neoteric ionic liquids (ILs) based on methyl carbonate anions. Initially, the COSMO-SAC model was performed to predict the infinite dilution activity coefficient values for the solubility of AB and EDAB on the pyrrolidinium-and ammonium-based cations. Based on the screening study, 1-butyl-1-methylpyrrolidinium methyl carbonate[Bmpyr][CH 3 CO 3 ] and tributylmethylammonium methyl carbonate [TBMA][CH 3 CO 3 ] were selected for our dehydrogenation studies. It was observed that the latter performed remarkably well in terms of equivalents of hydrogen released, which is primarily due to the higher stability of the intermediate in the polar medium of ILs. Here, [TBMA][CH 3 CO 3 ] gave a cumulative release of 3.50 equiv of hydrogen with EDAB at 105 °C. The 1 H NMR spectroscopy technique confirmed the catalytic sum solvent role of ILs. The electronic structure elucidation of individual ILs and IL−chemical hydride complexes was then performed at the M06-2X/6-311++G(d,p) level of theory. The DFT calculations, along with the highest occupied molecular orbital−lowest unoccupied molecular orbital analysis, pointed out the fact that the active sites mainly existed within the methyl carbonate anions. Overall, the dehydrogenation pathway was initiated by the formation of hydrogen-bonded interactions between the protic moieties of the hydrides and the anionic part of the ILs, respectively.
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