Calculated linear free energy relationships in the course of the Suzuki–Miyaura coupling reaction

The Substituent Effects of Suzuki Coupling in Aqueous Micelles

The Suzuki coupling in aqueous micelles has received much attention, but few attempts focus on its substituent effects. In view of the significant substituent effects on this reaction, it is necessary and practical to investigate its substituent effects. Herein, the substituent effects of Suzuki coupling in aqueous micelles are well established through Hammett plots and kinetic studies. In the cases of aryl halides, the rate-determining step of the reaction will shift from the oxidation addition step to the transmetalation step as the substituents' electron withdrawing ability increases, so aryl halides with weak electron-withdrawing groups exhibit better reactivity than ones containing strong electron-withdrawing or electron-donating groups. For arylboronic acids, the electron donating groups are beneficial to the Suzuki reaction, while the electron withdrawing group is unfavorable for the reaction. The Suzuki reactions of substituent exchange between arylboronic acids and aryl halides further confirm these substituent effects.

Scaling Relationships and Volcano Plots in Homogeneous Catalysis

Scaling relations and volcano plots are widely used in heterogeneous catalysis. In this Perspective, we discuss the prospects and challenges associated with the application of similar concepts in homogeneous catalysis using examples from the literature that have appeared recently.

Site-selective Suzuki-Miyaura coupling of heteroaryl halides - understanding the trends for pharmaceutically important classes

Suzuki-Miyaura cross-coupling reactions of heteroaryl polyhalides with aryl boronates are surveyed. Drawing on data from literature sources as well as bespoke searches of Pfizer's global chemistry RKB and CAS Scifinder® databases, the factors that determine the site-selectivity of these reactions are discussed with a view to rationalising the trends found.

Accessing and predicting the kinetic profiles of homogeneous catalysts from volcano plots

Volcano plots, which generally describe only thermodynamics, are expanded to include kinetics that markedly influence the performance of homogeneous catalysts.

Volcano plots are frequently used as aids in the search for new heterogeneous and electrochemical catalysts. These tools successfully predict catalytic processes based solely on thermodynamic descriptions, which also capably describe many aspects of the catalytic cycles of homogeneous species. However, homogeneous catalysts also frequently depend upon the kinetic influences brought about by steric interactions to promote or prevent specific chemical reactions. Here, a prototypical transformation facilitated by a homogeneous catalysis, the hydroformylation of an olefin using CO and H₂, is examined to establish the viability of creating kinetic volcano plots and to determine their ability to ascertain the influences steric bulk plays on catalytic cycle energetics. Similar to their thermodynamic counterparts, kinetic volcanoes successfully reproduce many experimentally known facets of the hydroformylation reaction. In contrast to thermodynamic volcanoes, kinetic volcanoes emphasize changes in the height of the different activation barriers brought about by steric interactions. This crucial information, however, comes with considerable computational cost, since the transition states of catalysts bearing large bulky ligands must be identified and characterized. To overcome this drawback, a procedure is proposed that relates a simple steric parameter, the Tolman cone angle, with the descriptors used to create the kinetic volcano plots. In this way, the activation barriers of bulky catalysts can be estimated without requiring expensive transition state computations. These newly derived structure–activity relationship volcano plots represent useful tools for identifying new homogeneous catalysts.

Linear scaling relationships and volcano plots in homogeneous catalysis - revisiting the Suzuki reaction

Linear free energy scaling relationships and volcano plots are common tools used to identify potential heterogeneous catalysts for myriad applications. Despite the striking simplicity and predictive power of volcano plots, they remain unknown in homogeneous catalysis. Here, we construct volcano plots to analyze a prototypical reaction from homogeneous catalysis, the Suzuki cross-coupling of olefins. Volcano plots succeed both in discriminating amongst different catalysts and reproducing experimentally known trends, which serves as validation of the model for this proof-of-principle example. These findings indicate that the combination of linear scaling relationships and volcano plots could serve as a valuable methodology for identifying homogeneous catalysts possessing a desired activity through a priori computational screening.

Exploring a cascade Heck-Suzuki reaction based route to kinase inhibitors using design of experiments

Design of Experiments (DoE) has been used to optimize a diversity oriented palladium catalyzed cascade Heck-Suzuki reaction for the construction of 3-alkenyl substituted cyclopenta[b]indole compounds. The obtained DoE model revealed a reaction highly dependent on the ligand. Guided by the model, an optimal ligand was chosen that selectively delivered the desired products in high yields. The conditions were applicable with a variety of boronic acids and were used to synthesize a library of 3-alkenyl derivatized compounds. Focusing on inhibition of kinases relevant for combating melanoma, the library was used in an initial structure-activity survey. In line with the observed kinase inhibition, cellular studies revealed one of the more promising derivatives to inhibit cell proliferation via an apoptotic mechanism.

Transmetalation from B to Rh in the course of the catalytic asymmetric 1,4-addition reaction of phenylboronic acid to enones: a computational comparison of diphosphane and diene ligands

A DFT study on the transmetalation of PhB(OH)₂ to diphosphane and diene Rh catalysts confirms the proposed intermediate and reactivity trends.