The interionic structure of four gold(I) π-alkyne ion pairs, with general formula [(PR12R2)Au(η2-3-hexyne)]BF4 (R1 = R2 = tBu, 1a; R1 = tBu, R2 = o-diphenyl, 2a; R1 = R2 = 2,4,6-trimethoxyphenyl, 3a; R1 = R2 = 2,4-di-tert-butylphenoxy, 4a), was studied by 19F, 1H-HOESY NMR spectroscopy. In all the cases the anion locates mainly close to the alkyne, but the degree of specificity of location strongly depends on the P-ligand and it is high for ion pairs bearing poorly electron donating PR12R2 ligands (particularly, 4a) and low for ion pairs with strongly electron donating PR12R2 ones (such as 3a). This result is rationalized through relativistic DFT calculations, showing that the electronic properties of the P-ligand finely tune the charge accumulation on the alkyne and, consequently, its ability of attracting the anion.
Dalton Transactions
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