2 research outputs found
Time-Resolved 3D Hammett Correlation to Monitor Catalyst Behavior with No Differential Data in Hand
Hammett correlation is one of the
widely applied tools in the mechanistic
studies of catalytic processes. From the beginning, it was applied
for measuring reaction rates with various substituted substrates,
particularly benzoic acid derivatives (under competitive or noncompetitive
modes), to construct a two-dimensional plot of the relative reactivity
vs the Ļ-constant of the substituents. In this study, we use
time-resolved fundamental Hammett correlation to obtain a three-dimensional
plot for a catalytic reaction using experimental data of cross-coupling
reactions. Using this approach, possible variations of the Hammett
correlation parameter Ļ during the catalytic reaction can be
easily monitored. Importantly, the suggested approach does not require
differentiation of primary experimental kinetic data on the concentrations
of substrates and products. The study was conducted for the SuzukiāMiyaura
reaction, and demonstrative data were obtained for different behaviors
of the Pd species activating aryl iodides, aryl bromides, or aryl
chlorides under āligand-freeā catalytic conditions.
The proposed approach was tested for other reactions of aryl halides
and related substrates to confirm its validity for the monitoring
of possible changes in active catalyst species during the reactions
Mechanistic Study of Direct Arylation of Indole Using Differential Selectivity Measurements: Shedding Light on the Active Species and Revealing the Key Role of Electrophilic Substitution in the Catalytic Cycle
Differential selectivity
of the direct arylation of indole with
aryl halides under competing and noncompeting conditions with a varying
set of reaction parameters was determined using phase trajectories.
The results described herein allow for conclusions to be drawn regarding
the character of active complexes (cationic, neutral, or anionic)
as well as realization of the indole electrophilic substitution in
the catalytic cycle using the ligand-free catalytic system