Binding Interaction of the Trimethylsilyl Cation with Oxygen and Nitrogen Bases in the Gas Phase. Acetopheones, Benzaldehydes, Pyridines, Anilines, and N,N-Dimethylanilines

Abstract

The gas-phase basicities toward the trimethylsilyl cation, GB(Me3Si+), were determined for a series of acetophenones, benzaldehydes, pyridines, anilines, and N,N-dimethylanilines by measuring the equilibrium constants of trimethylsilyl cation transfer reactions. GB(Me3Si+) increases in the order aniline < benzaldehyde < acetophenone < N,N-dimethylaniline < pyridine, while GB(H+) increases as benzaldehyde < acetophenone < aniline < pyridine < N,N-dimethylaniline. The effects of ring substituents on the GB(Me3Si+) of the respective bases are, however, linearly correlated with the corresponding proton basicities with a slope of 0.8 to 1.0, showing family-dependent linear relationships. Furthermore, an analysis of the substituent effects on the GB(Me3Si+) of acetophenone and benzaldehyde showed that the ρ values are close to those for the proton basicities, though the resonance demand of Me3Si+ adduct ions is slightly reduced compared with that for the protonated ones. DFT calculations at the B3LYP/6-31+G(d) level of theory reproduced such a trend in substituent effects as well as the family-dependent linear correlations between the H+ and Me3Si+ basicities. Both the experimental and theoretical results lead to the conclusion that the binding interactions of Me3Si+ with O and N atoms of organic bases have a pronounced covalent character to a similar degree as that of a proton.

Experimental and theoretical studies of the binding interaction between copper(I) cation and the carbonyl group

“…(12)) is useful [28]. Indeed, it has been applied successfully not only to GB but also to Li + [19], Me 3 Si + [20], and Me 3 Ge + basicities of acetophenones [21], and the obtained results have helped our understanding of the nature of the bond between Lewis acids and neutral ligands.…”

“…For this purpose, a particular interesting subset of ligands is aromatic compounds with a single basic site of which the electronic properties can be varied by the remote ring-substituent. Recently, we applied this approach to the study of the binding interaction of the lithium cation as well as other Lewis cation such as Me 3 Si + and Me 3 Ge + with neutral organic molecules [19][20][21]. The same approach will be applied to the interaction between copper cation and organic ligands.…”

“…The same approach will be applied to the interaction between copper cation and organic ligands. In this study, we therefore determined the copper cation basicity for m-and p-substituted acetophenones of which thermodynamic data such as gas phase basicities and Lewis cation basicities are available for comparison [19][20][21][22].…”

Gas‐phase basicities of acetophenones toward lanthanum cation [La(OMe)]

“…It is now possible to compare the corresponding results for a series of Lewis cation basicities of the acetophenone system. The ρ value decreases in the order of H + (−11.6) > Me 3 Si + (−11.0) > Me 3 Ge + (−9.7) > Cu + (−9.3) > Li + (−8.3) > La(OMe) (−7.0) 9–11, 18, 19, 21. The smallest ρ value for the La(OMe) basicity may be consistent with the largely ionic (ion–dipole interaction) nature of the binding interaction between La(OMe) and the carbonyl oxygen atom and with a larger ionic radii of La(OMe) than Li + because the electrostatic interaction decreases as the distance between a charge center and the substituent increases.…”

“…The contribution of the resonance effect involved in the stability of the La(OMe) complex will be described in terms of the Yukawa–Tsuno (Y–T) equation (Eqn 13)14–17 as applied successfully in the previous studies 10, 11, 18, 19 …”