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Steric and Electronic Effects on the Heterolytic H(2)-Splitting by Phosphine-Boranes R(3)B/PR '(3) (R = C(6)F(5), Ph; R ' = C(6)H(2)Me(3), tBu, Ph, C(6)F(5), Me, H): A Computational Study

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Steric and Electronic Effects on the Heterolytic H(2)-Splitting by Phosphine-Boranes R(3)B.htm (404bytes)
Date
2011-10-26
Author
Gao, Shulin
Wu, Wei
吴玮
Mo, Yirong(Western Michigan Univ, Dept Che)
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  • 化学化工-已发表论文 [14237]
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Abstract
The steric and electronic effects exerted by the substituents R/R' on the heterolytic H(2)-splitting by phosphine-boranes R(3)B/PR'(3) [R = C(6)F(5) (1), Ph (2); R' = C(6)H(2)Me(3) (a), tBu (b), Ph (c), C(6)F(5) (d), Me (e), H (f)] have been studied by performing quantum mechanical density functional theory and RI-MP2 calculations. Energy decomposition analyses based on the block-localized wavefunction method show that the nature of the interaction between R(3)B and PR'(3) is strongly dependent on the B-P distance. With short B-P distances (similar to 2.1 angstrom), the strength of Lewis pairs results from the balance among various energy terms, and both strong and weak dative bonds can be found in this group. However, at long B-P distances (>4.0 angstrom), the correlation and dispersion energy (Delta E(corr)) dominates. In other words, the van der Waals (vdW) interaction rules these weakly bound complexes. No ion-pair structures of 1f and 2c-2f can be located as they instantly converge to vdW complexes R(3)B center dot center dot center dot H(2)center dot center dot center dot PR'(3). We thus propose a model, which predicts that when the sum (E(hp)) of the hydride affinity (HA) of BR(3) and the proton affinity (PA) of PR'(3) is higher than 340.0 kcal/mol, the ion-pair [R(3)BH(-)][HPR'(+)(3)] can be observed, whereas with E(hp) below this value, the ion pair would instantly undergo the combination of proton and hydride with the release of H(2). The overall reaction energies (1a-1e and 2a-2b) can be best described by a fitting equation with HA(BR(3)), PA(PR'(3)), and the binding energy Delta E(b)(BR(3)/PR'(3)) as predictor variables: Delta E(R)([R(3)BH(-)][HPR'(+)(3)]) = -0.779HA(BR(3)) - 0.695PA(PR'(3)) - 1.331 Delta E(b)(zpe,cp) (BR(3)/PR'(3)) + 245.3 kcal/mol. The fitting equation provides quantitative insights into the steric and electronic effects on the thermodynamic aspects of the heterolytic H(2)-splitting reactions. The electronic effects are reflected by HA(BR(3)) and PA(PR'(3)), and Delta E(b) can be significantly influenced by the steric overcrowding. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 3761-3775, 2011
Citation
INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY,2011,111(14):3761-3775
URI
http://dx.doi.org/doi:10.1002/qua.22901
https://dspace.xmu.edu.cn/handle/2288/11457
WOS:000295366300030

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