Parametrization of Catalytic Organic Reactions with Convex Hammett Plots

Abstract

Quantification is essential to fairly compare between synthetic reactions in chemistry. Here we propose two new parameters called “adapted sensitivity constant” (ρadap) and “substrate electronics adaptability” (SEA), easily obtainable from Hammett plots, to assess the ability of a (catalytic) reaction to transform substrates with opposing electronics. These new parameters allow one to list reactions, catalyzed or not, as a function of substrate scope.

Phosphines on Colloidal Nickel Nanocatalysts to Lower the Onset Temperature of Terminal Alkynes Hydrogenation

“…For five-substituted alkynes, we investigated the influence of the presence of 0.2 equiv of P n Bu 3 (Table ). The table was ordered according to their Hammett parameter for para-substituents, which is 0 for phenylacetylene (entry 5) and varies from −0.27 to 0.54 for the other alkynes . The substitution in the para position was expected to have a limited effect on the steric hindrance at the alkyne moiety, while it should have a strong effect on its electronic properties.…”

Microwave-Assisted Synthesis of E-Aldimines, N-Heterocycles, and H2 by Dehydrogenative Coupling of Benzyl Alcohol and Aniline Derivatives Using CoCl2 as a Catalyst

“…This resulted in a V-shaped curve with a negative slope having ρ = −3.53 for electron-donating substituents, whereas a positive slope with ρ = 2.71 for electron-withdrawing ones. The analysis of this curve suggests the formation of an intermediate with positive charge density (TS-A) (Figure c, inset) for electron-donating substrates and negative charge density for electron-withdrawing substrates (TS-B) (Figure c, inset) …”

“…The analysis of this curve suggests the formation of an intermediate with positive charge density (TS-A) (Figure 3c, inset) for electron-donating substrates and negative charge density for electron-withdrawing substrates (TS-B) (Figure 3c, inset). 24 Such a Hammett plot indicates that, for electron-donating groups, the reaction may initiate from the lone pair of the N atom, whereas for electron-withdrawing groups, deprotonation from the N atom (more acidic H′s) may lead to the negative charge density on the intermediate (TS-B). The latter mechanism may not be stable enough, as it involves two negative charge centers near vicinity, which justifies the poor yield of the products with electron-withdrawing groups over the aniline system (Scheme 3).…”

MOF-Triggered Synthesis of Subnanometer Ag02 Clusters and Fe3+ Single Atoms: Heterogenization Led to Efficient and Synergetic One-Pot Catalytic Reactions

“…In view of the good matching in catalytic activity between AgNO 3 (+TEMPO) and Fe 3+ Ag 0 2 @MOF, we wondered if the true active Ag species in solution were also Ag 0 2 , formed in situ under the reaction conditions. 64 The formation of ultrasmall noble metal clusters in solution during organic reactions when starting from metal salts is well-established in the literature 19,33 and is based on the tendency of the noble metal salt, without stabilizing ligands, to reduce and aggregate but, at the same time, to be stabilized in the form of metastable ultrasmall clusters by the action of the reactants/products. The monitoring of the reaction using AgNO 3 and TEMPO (entry 3) by UV−vis absorption and emission spectrophotometry does not show the presence of plasmonic Ag nanoparticles (Figure S16), but the appearance of fluorescence bands that are compatible with the formation of Ag 2−10 clusters during the reaction (Figure S17).…”

“…In view of the good matching in catalytic activity between AgNO 3 (+TEMPO) and Fe 3+ Ag 0 2 @MOF , we wondered if the true active Ag species in solution were also Ag 0 2 , formed in situ under the reaction conditions . The formation of ultrasmall noble metal clusters in solution during organic reactions when starting from metal salts is well-established in the literature , and is based on the tendency of the noble metal salt, without stabilizing ligands, to reduce and aggregate but, at the same time, to be stabilized in the form of metastable ultrasmall clusters by the action of the reactants/products.…”