Cation affinity numbers of Lewis bases

Abstract

SummaryUsing selected theoretical methods the affinity of a large range of Lewis bases towards model cations has been quantified. The range of model cations includes the methyl cation as the smallest carbon-centered electrophile, the benzhydryl and trityl cations as models for electrophilic substrates encountered in Lewis base-catalyzed synthetic procedures, and the acetyl cation as a substrate model for acyl-transfer reactions. Affinities towards these cationic electrophiles are complemented by data for Lewis-base addition to Michael acceptors as prototypical neutral electrophiles.

The Lewis Acidity of the BO Triple Bond in Methyl(oxo)­borane

“…The interaction strength increases along the series NH 3 < py < NMe 3 < imidazole < py‐NH 2 < DMAP. This trend is similar to the basicitiy of nitrogen bases towards the methyl cation,41 with the only exception that imidazole binds towards 1 more strongly than NMe 3 . What is surprising is the small size of the interaction energy.…”

“…Based on the methyl cation affinity, imidazole lies between pyridine and DMAP in base strength 41. The lengths of the BN and BO bonds in 1· imidazole are indeed between the values computed for 1· py and 1· DMAP.…”

Annelated Pyridines as Highly Nucleophilic and Lewis Basic Catalysts for Acylation Reactions

“…[7] These data show that the additional amino-sub-stituents attached to the 3-and 5-position of pyridines 4 and 5 further increase the Lewis basicity relative to the allcarbon analogue 3. [7] These data show that the additional amino-sub-stituents attached to the 3-and 5-position of pyridines 4 and 5 further increase the Lewis basicity relative to the allcarbon analogue 3.…”

Morita–Baylis–Hillman Reactions with Nitroalkenes: A Case Study

“…We can, however, get around this lack of information by calculating the ratio of equilibrium constants for s-DMAP and DMAP (K s-DMAP / K DMAP ) with Equation (3). This stability can also be evaluated by using the "methyl cation affinity" (MCA), a thermodynamic parameter that is easily and accurately calculated, [20] which represents the energy necessary to strip off a methyl cation from the corresponding methylammonium species. This ratio says that the s-DMAP-derived zwitterion is four times more stable than its DMAP-derived congener.…”