Journal
DALTON TRANSACTIONS
Volume 50, Issue 2, Pages 722-728Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/d0dt03972a
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Funding
- EPSRC [EP/R004064/1]
- Leverhulme Trust [RPG-2014-317]
- University of Nottingham
- European Research Council under H2020/ERC Consolidator Grant topDFT [772259]
- European Research Council (ERC) [772259] Funding Source: European Research Council (ERC)
- EPSRC [EP/R004064/1] Funding Source: UKRI
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The effect of para-substitution on a series of m-terphenyl lithium complexes has been investigated. X-ray crystallography shows structural similarity, while in-depth NMR spectroscopic studies reveal notable electronic differences, correlated with the nature of the substituents.
The effect of para-substitution upon the structural and electronic properties of a series of m-terphenyl lithium complexes [R-Ar#-Li](2) (R = t-Bu 1, SiMe3 2, H 3, Cl 4, CF3 5; where R-Ar-# = 2,6-{2,6-Xyl}(2)-4R-C6H2 and 2,6-Xyl = 2,6-Me2C6H3) has been investigated. X-ray crystallography reveals the complexes to be structurally similar, with little variation in C-M-C bond lengths and angles across the series. However, in-depth NMR spectroscopic studies reveal notable electronic differences, showing a linear correlation between the Li-7{H-1} NMR chemical shifts of the para-substituted complexes and their Hammett constants. The flanking methyl protons exhibit a similar electronic shift in the H-1 NMR spectra, which has been rationalised by the presence of through-space Li center dot center dot center dot H interactions, as evidenced by two-dimensional Li-7-H-1 heteronuclear Overhauser spectroscopy (HOESY). In both cases, electron-withdrawing substituents are found to cause an upfield peak shift. A computational analysis is employed to account for these trends.
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