Ligand-Driven Advances in Iridium-Catalyzed sp3 C–H Borylation: 2,2′-Dipyridylarylmethane

Abstract

The field of catalytic C–H borylation has grown considerably since its founding, providing a means for the preparation of synthetically versatile organoborane products. Although sp2 C–H borylation methods have found widespread and practical use in organic synthesis, the analogous sp3 C–H borylation reaction remains challenging and has seen limited application. Existing catalysts are often hindered by incomplete consumption of the diboron reagent, poor functional-group tolerance, harsh reaction conditions, and the need for excess or neat substrate. These challenges acutely affect the C–H borylation chemistry of unactivated hydrocarbon substrates, which has lagged in comparison to methods for the C–H borylation of activated compounds. Herein, we discuss recent advances in the sp3 C–H borylation of undirected substrates in the context of two particular challenges: (1) utilization of the diboron reagent and (2) the need for excess or neat substrate. Our recent work on the application of dipyridylarylmethane ligands in sp3 C–H borylation has allowed us to make contributions in this space and has presented an additional ligand scaffold to supplement traditional phenanthroline ligands.

Metal‐Free Directed Site‐Selective Csp3‐H Borylation of Saturated Cyclic Amines

“…While transition-metal (TM) catalyzed Csp 2 À H borylation methodologies are widespread, the catalytic borylation of Csp 3 À H substrates are uniquely challenging because of the sterically demanding geometry of Csp 3 À H compared to planar Csp 2 À H and the absence of easily accessible frontier molecular orbitals for coordination with the catalysts. [25] TM catalyzed methodologies for the CÀ H functionalization of cyclic amine frameworks have been developed using directing groups, [26][27][28][29][30][31][32][33] such as pyridine as pioneered by the Sawamura group using Rh [28] and Ir [29] complexes (Figure 1a).…”

Metal‐Free B−B Dehydrocoupling Reaction of a Simple Borane Adduct: Convenient Access to a Nucleophilic Diborane(4)

“…Diborane (4) molecules with a direct boron-boron single bond are widely applied in synthetic chemistry, e.g., for the mono-and di-borylation of unsaturated and saturated substrates, [1][2][3][4][5] that serve as valuable linchpins for CÀ C bond formations. Traditionally, diborane(4) molecules are synthesized by reduction of a mononuclear haloborane.…”

Metallfreie B−B Dehydrokupplung eines Einfachen Boran‐Addukts: Bequemer Zugang zu einem Nukleophilen Diboran(4)

“…Diboran(4)‐Moleküle mit einer direkten Bor‐Bor‐Einfachbindung finden in der synthetischen Chemie breite Anwendung, z. B. für die Mono‐ und Diborylierung von ungesättigten und gesättigten Substraten, [1–5] die wertvolle Schlüsselschritte in der Bildung von C−C‐Bindungen darstellen. Traditionell werden Diboran(4)‐Moleküle durch Reduktion eines einkernigen Haloborans synthetisiert.…”

“…Diboran(4)-Moleküle mit einer direkten Bor-Bor-Einfachbindung finden in der synthetischen Chemie breite Anwendung, z. B. für die Mono-und Diborylierung von ungesättigten und gesättigten Substraten, [1][2][3][4][5] Die Dehydrokupplungsroute ist wirtschaftlicher und nachhaltiger als die Reduktionsroute, da sie den Einsatz stöchiometrischer Mengen eines Reduktionsmittels vermeidet und nur hochwertiger Wasserstoff als Koppelprodukt entsteht. Dehydrokupplungsreaktionen wurden für verschiedene p-Block-Elemente untersucht, sowohl für Homo-als auch für Heterokupplungsreaktionen.…”