Molecular Salt Effects in the Gas Phase: Tuning the Kinetic Basicity of [HCCLiCl]− and [HCCMgCl2]− by LiCl and MgCl2 |
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| Authors: | Dr George N Khairallah Dr Gabriel da Silva Prof Richard A J O'Hair |
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| Affiliation: | 1. School of Chemistry and Bio21 Institute, University of Melbourne, Melbourne, Victoria 3010 (Australia);2. ARC Centre of Excellence for Free‐Radical Chemistry and Biotechnology;3. Department of Chemical and Biomolecular Engineering, The University of Melbourne, Melbourne, Victoria 3010 (Australia) |
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| Abstract: | A combination of gas‐phase ion–molecule reaction experiments and theoretical kinetic modeling is used to examine how a salt can influence the kinetic basicity of organometallates reacting with water. HC?CLiCl]? reacts with water more rapidly than HC?CMgCl2]?, consistent with the higher reactivity of organolithium versus organomagnesium reagents. Addition of LiCl to HC?CLiCl]? or HC?CMgCl2]? enhances their reactivity towards water by a factor of about 2, while addition of MgCl2 to HC?CMgCl2]? enhances its reactivity by a factor of about 4. Ab initio calculations coupled with master equation/RRKM theory kinetic modeling show that these reactions proceed via a mechanism involving formation of a water adduct followed by rearrangement, proton transfer, and acetylene elimination as either discrete or concerted steps. Both the energy and entropy requirements for these elementary steps need to be considered in order to explain the observed kinetics. |
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| Keywords: | ab initio calculations gas‐phase reactions mass spectrometry organometallic compounds salt effect |
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