Iridium-Catalyzed Regioselective Borylation through C-H Activation and the Origin of Ligand-Dependent Regioselectivity Switching

Computational tools for the prediction of site- and regioselectivity of organic reactions

The regio- and site-selectivity of organic reactions is one of the most important aspects when it comes to synthesis planning. Due to that, massive research efforts were invested into computational models for regio- and site-selectivity prediction, and the introduction of machine learning to the chemical sciences within the past decade has added a whole new dimension to these endeavors. This review article walks through the currently available predictive tools for regio- and site-selectivity with a particular focus on machine learning models while being organized along the individual reaction classes of organic chemistry. Respective featurization techniques and model architectures are described and compared to each other; applications of the tools to critical real-world examples are highlighted. This paper aims to serve as an overview of the field's status quo for both the intended users of the tools, that is synthetic chemists, as well as for developers to find potential new research avenues.

Theoretical Insight into the Multiple Roles of the Silyl-Phenanthroline Ligand in Ir-Catalyzed C(sp3)-H Borylation

Silyl-phenanthroline (NN'Si) ligand ancillary iridium-catalyzed C(sp3)-H borylation is investigated theoretically. Density functional theory calculations clearly disclose that the (NN'Si)IrV(H)(Bpin)3 (NN'Si = 6-[(di-tert-butylsilyl)methyl]-1,10-phenanthroline) complex is a resting state, and the (NN'Si)IrIII(Bpin)2 complex serves as an active species in the catalytic cycle. The remarkably high activity of this type of a catalyst arises from the rapid reductive elimination of HBpin from (NN'Si)IrV(H)(Bpin)3 to generate the active species (NN'Si)IrIII(Bpin)2. The silyl group plays a crucial role in accelerating the crucial hydride-migration elementary step, which allows the isomerization of the (NN'Si)IrV(R)(H)(Bpin)2 intermediate to achieve the C(sp3)-B reductive elimination and afford the borylated product. Although C(sp3)-H borylation with HBpin is thermodynamically unfavorable, the Ir-dihydride intermediate (NN'Si)IrV(H)2(Bpin)2 generated after product formation is slightly more stable than resting-state (NN'Si)IrV(H)(Bpin)3 in this catalytic cycle, which is an important driving force for the HBpin reaction. Such success was not attained by many other traditional bidentate ligands. The unique regioselectivity of n-butyl ethyl ether and 2-methylheptane, induced by the NN'Si-pincer ligand, is well reproduced and the underlying reason for the selectivity is clearly elucidated.