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. 2024 Mar 20;146(11):7124-7129.
doi: 10.1021/jacs.3c12981. Epub 2024 Mar 8.

2-Aminophenanthroline Ligands Enable Mild, Undirected, Iridium-Catalyzed Borylation of Alkyl C-H Bonds

Isaac F Yu  1 , Kyan A D'Angelo  1 , Ángel D Hernandez-Mejías  1 , Nanrun Cheng  1 , John F Hartwig  1
Affiliations

2-Aminophenanthroline Ligands Enable Mild, Undirected, Iridium-Catalyzed Borylation of Alkyl C-H Bonds

Isaac F Yu et al. J Am Chem Soc. .

Abstract

The catalytic, undirected borylation of alkyl C-H bonds typically occurs at high reaction temperatures or with excess substrate, or both, because of the low reactivity of alkyl C-H bonds. Here we report a new iridium system comprising 2-anilino-1,10-phenanthroline as the ligand that catalyzes the borylation of alkyl C-H bonds with little to no induction period and with high reaction rates. This superior activation and reactivity profile of 2-aminophenanthroline-ligated catalysts leads to broader reaction scope, including reactions of sensitive substrates, such as epoxides and glycosidic acetals, enhanced diastereoselectivity, and higher yields of borylated products. These catalysts also enable the borylation of alkanes, amines, and ethers at room temperature for the first time. Mechanistic studies imply that facile N-borylation occurs under the reaction conditions and that iridium complexes containing N-boryl aminophenanthrolines are competent precatalysts for the reaction.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1.
Figure 1.
Prior reports of undirected borylation of alkyl C–H bonds with limiting or near-limiting quantities of substrate and this work on milder reactions and facile activation with aminophenanthroline ligands.
Figure 2.
Figure 2.
Illustration of a possible mode for activation of catalysts containing 2-mphen and design of modular and tunable ligands for more rapid activation.
Figure 3.
Figure 3.
Evaluation of the reactivity of 2-aminophenthrolines. Time courses of the borylation of tetrahydrofuran with either 2-mphen or a variety of 2-aminophenanthrolines at 100 °C.
Figure 4.
Figure 4.
Mechanistic experiments. (a) KIE for the borylation of THF. (b) Synthesis of N-borylated 2-aminophenanthroline L5. (c) Synthesis of an iridium trisboryl complex containing L5. (d) Catalytic reactivity of (L5)Ir(Bpin)3.
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