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B-NMR shielding effects in the closo borane series. Sensitivity of shifts and their additivity

Abstract

Alpha Shift Correlation (ASC) method is used to assess quantitatively NMR shielding effects in a series of halogen derivatives of closo-borane dianions, [Xm-BnHn-m]2- There is a simple linear correlation between the universal αref shifts and those induced by the substituent X in all positions of the closo borane cluster:Δδ(11B) = k.αref (where  Δδ = δs - δp and subscripts s and p relate to the substituted and parent derivative, respectively; k = correlation slope). The sensitivity of the chemical shift in a given cage position to X-changes is defined by the g factor (g = gradient =k.102). The ASC approach revealed that α-deshielding effect in the monosubstituted anionic [X-BnHn-1]2- series decreases in the order of n: 6 > 12 > 10 > 9, being dependent of the cage type and electron density at the substituted vertex. The sensitivity (g) in individual cluster positions to substituent changes decreases in the order: α >> A > β > γ and is of approximately additive character. The most important feature of the unsubstituted sphere is the antipodal (A) effect showing a g-trend inversed to that observed at the substituted α-sites. Of interest are also the remarkable pseudo-A and trans-γ shielding effects in the 9- and 10-vertex anionic series.

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Publication details

The article was received on 23 Jul 2017, accepted on 28 Sep 2017 and first published on 28 Sep 2017


Article type: Paper
DOI: 10.1039/C7NJ02689G
Citation: New J. Chem., 2017, Accepted Manuscript
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    B-NMR shielding effects in the closo borane series. Sensitivity of shifts and their additivity

    B. Stibr, New J. Chem., 2017, Accepted Manuscript , DOI: 10.1039/C7NJ02689G

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