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Issue 23, 2017
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11B-NMR shielding effects in the closo borane series: sensitivity of shifts and their additivity

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Abstract

An Alpha Shift Correlation (ASC) method is used to assess quantitatively NMR shielding effects in a series of halogen derivatives of closo-borane dianions, [Xm-BnHnm]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 = δsδp and subscripts s and p denote the substituted and parent derivatives, 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 the α-deshielding effect in the monosubstituted anionic [X-BnHn−1]2− series decreases in the order of n: 6 > 12 > 10 > 9, and is dependent on the cage type and electron density at the substituted vertex. The sensitivity (g) in individual cluster positions to substituent changes decreases in the order αA > 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.

Graphical abstract: 11B-NMR shielding effects in the closo borane series: sensitivity of shifts and their additivity

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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., 2017,41, 14452-14456
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    11B-NMR shielding effects in the closo borane series: sensitivity of shifts and their additivity

    B. Štíbr, New J. Chem., 2017, 41, 14452
    DOI: 10.1039/C7NJ02689G

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