Protonation of phenylboronic acid: Comparison of G3B3 and G2MP2 methods |
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| Authors: | Senjuti De Michael G B Drew David W Price Samik Nag Dipankar Datta |
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| Institution: | 1. Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700 032, India;2. School of Chemistry, The University, Whiteknights, Reading RG6 6AD, United KingdomSchool of Chemistry, The University, Whiteknights, Reading RG6 6AD, United Kingdom;3. School of Chemistry, The University, Whiteknights, Reading RG6 6AD, United Kingdom;4. A. W. E. Aldermaston, Reading RG4 7P, United Kingdom |
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| Abstract: | G3B3 and G2MP2 calculations using Gaussian 03 have been carried out to investigate the protonation preferences for phenylboronic acid. All nine heavy atoms have been protonated in turn. With both methodologies, the two lowest protonation energies are obtained with the proton located either at the ipso carbon atom or at a hydroxyl oxygen atom. Within the G3B3 formalism, the lowest‐energy configuration by 4.3 kcal · mol?1 is found when the proton is located at the ipso carbon, rather than at the electronegative oxygen atom. In the resulting structure, the phenyl ring has lost a significant amount of aromaticity. By contrast, calculations with G2MP2 show that protonation at the hydroxyl oxygen atom is favored by 7.7 kcal · mol?1. Calculations using the polarizable continuum model (PCM) solvent method also give preference to protonation at the oxygen atom when water is used as the solvent. The preference for protonation at the ipso carbon found by the more accurate G3B3 method is unexpected and its implications in Suzuki coupling are discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 |
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| Keywords: | phenylboronic acid Suzuki coupling ab initio calculation acid– base behavior |
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