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Although nucleophilic aromatic substitution (S N Ar) is routinely employed as a practical alternative to transition-metal-catalyzed cross-coupling, the mechanistic basis for reactivity and regioselectivity remains underexplored and is an active area of research. This article reports a S N Ar-based etherification of 2,4-difluoroarylcarboxamides as a model system and shows that the ortho / para regioselectivity spans >500:1 to 1:∼20 simply by varying the reaction conditions via high-throughput experimentation (HTE). An in-depth characterization of the ortho -selective lead conditions is presented, and these insights are used to build a reactivity model that self-consistently accounts for the regioselectivity and reaction scope. This article discusses synthetic implications of condition-dependent magnesium coordination and Schlenk equilibria and demonstrates that consideration of molecular-level stoichiometry and isomerism is an essential prerequisite for rationalizing reactivity and regioselectivity in S N Ar.

Although screening technology has heavily impacted the fields of metal catalysis and drug discovery, its application to the discovery of new catalyst classes has been limited. The diversity of on- and off-cycle pathways, combined with incomplete mechanistic understanding, means that screens of potential new ligands have thus far been guided by intuitive analysis of the metal binding potential. This has resulted in the discovery of new classes of ligands, but the low hit rates have limited the use of this strategy because large screens require considerable cost and effort. Here, we demonstrate a method to identify promising screening directions via simple and scalable computational and linear regression tools that leads to a substantial improvement in hit rate, enabling the use of smaller screens to find new ligands. The application of this approach to a particular example of Ni-catalyzed cross-electrophile coupling of aryl halides with alkyl halides revealed a previously overlooked trend: reactions with more electron-poor amidine ligands result in a higher yield. Focused screens utilizing this trend were more successful than serendipity-based screening and led to the discovery of two new types of ligands, pyridyl oxadiazoles and pyridyl oximes. These ligands are especially effective for couplings of bromo- and chloroquinolines and isoquinolines, where they are now the state of the art. The simplicity of these models with parameters derived from metal-free ligand structures should make this approach scalable and widely accessible.

Cross-electrophile coupling has emerged as an attractive and efficient method for the synthesis of C(sp 2 )-C(sp 3 ) bonds. These reactions are most often catalyzed by nickel complexes of nitrogenous ligands, especially 2,2'-bipyridines. Precise prediction, selection, and design of optimal ligands remains challenging, despite significant increases in reaction scope and mechanistic understanding. Molecular parameterization and statistical modeling provide a path to the development of improved bipyridine ligands that will enhance the selectivity of existing reactions and broaden the scope of electrophiles that can be coupled. Herein, we describe the generation of a computational ligand library, correlation of observed reaction outcomes with features of the ligands, and the in silico design of improved bipyridine ligands for Ni-catalyzed cross-electrophile coupling. The new nitrogen-substituted ligands display a 5-fold increase in selectivity for product formation versus homodimerization when compared to the current state of the art. This increase in selectivity and yield was general for several cross-electrophile couplings, including the challenging coupling of an aryl chloride with an N -alkylpyridinium salt.