A combined NMR/DFT study on the ion pair structure of [(PR1(2)R2)Au(η2-3-hexyne)]BF4 complexes

The interionic structure of four gold(i) π-alkyne ion pairs, with general formula [(PR(1)(2)R(2))Au(η(2)-3-hexyne)]BF(4) (R(1) = R(2) = (t)Bu, 1a; R(1) = (t)Bu, R(2) = o-diphenyl, 2a; R(1) = R(2) = 2,4,6-trimethoxyphenyl, 3a; R(1) = R(2) = 2,4-di-tert-butylphenoxy, 4a), was studied by (19)F, (1)H-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 PR(1)(2)R(2) ligands (particularly, ) and low for ion pairs with strongly electron donating PR(1)(2)R(2) 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.