Understanding the Activation of Air-Stable Ir(COD)(Phen)Cl Precatalyst for C–H Borylation of Aromatics and Heteroaromatics

Abstract

A newly developed robust catalyst [Ir­(COD)­(Phen)­Cl] (A) was used for the C–H borylation of three dozen aromatics and heteroaromatics with excellent yield and selectivity. Activation of the catalyst was identified by the use of catalytic amounts of water, alcohols, etc., when B2pin2 was used in noncoordinating solvents, while for THF catalytic use of HBpin was required. The results were on par with the in situ based expensive system [Ir­(OMe)­(COD)]2/dtbbpy or Me4Phen.

Meta Selective C–H Borylation of Sterically Biased and Unbiased Substrates Directed by Electrostatic Interaction

“…From this selectivity pattern with electronically different bipyridine ligands, it may be stated that the electron-withdrawing bis-CF 3 groups attached with the bipyridine ligand ( L3 ) pull the electron from the ligand system, making it more electropositive after coordination with the iridium that interacts well with the partial negatively charged oxygen atom of the functional group of the arene via an electrostatic interaction. Next, we considered electronically different 1,10-phenanthroline ligands that are not much explored in C–H borylations. , The 1,10-phenanthroline is a rigid, planar, electron-poor heteroaromatic chelating ligand. Moreover, the two N-donor atoms point inward and are juxtaposed to each other in contrast to the bipyridine ligand.…”

“…Next, we considered electronically different 1,10-phenanthroline ligands that are not much explored in C−H borylations. 45,46 The 1,10-phenanthroline is a rigid, planar, electron-poor heteroaromatic chelating ligand. Moreover, the two N-donor atoms point inward and are juxtaposed to each other in contrast to the bipyridine ligand.…”

Rhodium and Iridium Mediated C-H and O-H Bond Activation of Two Schiff Base Ligands: Synthesis, Characterization and Catalytic Properties of the Organometallic Complexes

“…In the last step, elimination of HCl takes place, which is believed to be facilitated by the closeness of Ir-Cl bond to the phenolic O-H fragment in the iridium(III) intermediate, and thus the organoiridium complexes are obtained as end products. It is relevant to mention here that like rhodium(I), iridium(I) is also known to bring about C-H bond activation (Boutry et al, 1997;Tang et al, 2009;Press et al, 2016;Hung et al, 2021;Liu et al, 2021;Slack and Colacot, 2021;Yoshino and Matsunaga, 2021).…”

Effect of Pincer Methylation on the Selectivity and Activity in (PNP)Cobalt-Catalyzed C(sp2)–H Borylation

“…Metal-catalyzed methods for selective C­(sp 2 )–H functionalization are attractive strategies for the synthesis of ubiquitous organic molecules or late-stage active pharmaceutical ingredients. − Among different functionalization reactions, the borylation of C­(sp 2 )–H bonds is particularly powerful due to the synthetic versatility of the organoboron products. ,− Following the pioneering work of Smith, Maleczka, and Hartwig where borylation of arenes using [(η 5 -C 5 Me 5 )­Ir] precatalysts was demonstrated, − iridium catalysts for direct borylation of arenes and heteroarenes with increased rates and high yields have been extensively studied including iridium­(I) complexes with phosphine or bipyridine- and phenanthroline-derived ligands. − The combination of [Ir­(OMe)­(COD)] 2 (COD = 1,5-cyclooctadiene) and bipyridine or phenanthroline ligands is now one of the most widely used catalysts for C­(sp 2 )–H borylation. These catalysts exhibit high activity and often predictable site selectivity, where sterically accessible arene and heteroarene C­(sp 2 )–H bonds are functionalized preferentially .…”