Computational studies on the reactivity of alkyl halides over (Al₂O₃)_nnanoclusters: an approach towards room temperature dehydrohalogenation

Abstract

The role of alumina nanoclusters as a catalyst on the reactivity of alkyl halides has been explored. The thermochemical data obtained from Density Functional Theory (DFT) calculations and the analyses of the transition structures reveal that, between the two competing reactions, elimination (via E2) versus dissociative addition (via SN2), elimination is the kinetically controlled one and thus at room temperature, olefin is the major product. The results are in excellent agreement with the recent experimental observation where more than 97% of ethylene is formed at room temperature with the reaction of ethyl fluoride over an alumina surface, although the dissociative addition product is being thermodynamically more stable. We have tried to rationalize the fact by using alumina clusters of different sizes as well as different alkyl halides having β-H for elimination. It has been shown that, during the elimination (E2) pathway, the transition structure is oriented in such a way that the eliminating halogen and the β-H are in the interacting position with the three-centered Al and two-centered O atoms, respectively, where the Lewis acid/base interaction is the main guiding factor. We have also shown a possible pathway for regenerating the catalyst. Finally, the possibility of the reactions has been tested in the presence of H2O to mimic the same on the hydrated alumina surface.

Electronic Structure of Atomically Dispersed Supported Iridium Catalyst Controls Iridium Aggregation

“…21 Biswas and coworkers used (Al2O3)n clusters for n = 3, 4, and 6 to have a valid model for -Al2O3 with a (110) pattern for the Al2O3 surface, whereby they reported the thermodynamic stability of the bulk structure of -Al2O3. 22 Thus, the (100) surface of the Al12O18 cluster reported by Biswas et al was used to simulate the -Al2O3-supported Ir(CO)2 and Ir(C2H4)2 complexes. 22 For MgO, the (100) crystal was used as reported in our previous work.…”

“…22 Thus, the (100) surface of the Al12O18 cluster reported by Biswas et al was used to simulate the -Al2O3-supported Ir(CO)2 and Ir(C2H4)2 complexes. 22 For MgO, the (100) crystal was used as reported in our previous work. 23 In addition, the IR carbonyl stretching frequencies of the supported Ir(CO)2 complexes have been calculated by taking into account scaling factor as 0.986.…”

Reactions involving some gas molecules through sequestration on Al12Be cluster: An electron density based study

“…Mainly transition metal complexes are known to activate CF bonds although recently main group elements (alumina as well as aluminum chlorofluoride) have been utilized to activate CF bonds . We would like to qualitatively compare our results in the case of C 2 H 5 F oxidative addition with the results obtained by Sarkar and coworkers who reported a value of 20.9 kcal/mol (using the M06‐2X functional and TZVP basis set) in the corresponding reaction on Al 8 O 12 cluster . Clearly, Al 12 Be can accelerate the C 2 H 5 F oxidative addition reaction at 298.15 K to a slightly greater extent.…”

Reductive Defluorination and Mechanochemical Decomposition of Per- and Polyfluoroalkyl Substances (PFASs): From Present Knowledge to Future Remediation Concepts

“…The formation of fluoride ions was traced by the application of a fluoride sensitive electrode (F-ISE). Bearing both Lewis acid aluminum sites and Brønstedt acidic OH functionalities at the surface, Al 2 O 3 has been shown to be a promising candidate in the activation of organohalides [ 121 ]. Based on FT-IR spectra, the initial mechanistic step was proposed to be the deprotonation of the carboxylic acid group by surface hydroxyl groups of alumina (see Figure 5 ).…”