Neopentylglycolborylation of ortho-Substituted Aryl Halides Catalyzed by NiCl₂-Based Mixed-Ligand Systems

Abstract

NiCl(2)-based mixed-ligand systems were shown to be very effective catalysts for the neopentylglycolborylation of aryl iodides, bromides, and chlorides bearing electron-rich and electron-deficient ortho-substituents. Although NiCl(2)-based single-ligand catalytic systems were able to mediate neopentylglycolborylation of selected substrates, they were not as effective for all substrates, highlighting the value of the mixed-ligand concept. Optimization of the Ni(II)-catalyzed neopentylglycolborylation of 2-iodoanisole and methyl 2-iodobenzoate demonstrated that, while the role of ligand and coligand in the conversion of Ni(II) precatalyst to Ni(0) active catalyst cannot be ignored, a mixed-ligand complex is likely present throughout the catalytic cycle. In addition, protodeborylation and hydrodehalogenation were demonstrated to be the predominant side reactions of Ni(II)-catalyzed borylation of ortho-substituted aryl halides containing the electron-deficient carboxylate substituents. Ni(II) complexes in the presence of H(2)O and Ni(0) are responsible for the catalysis of these side reactions.

Stoichiometric and Catalytic Aryl−Cl Activation and Borylation using NHC‐stabilized Nickel(0) Complexes

“…A mixed‐ligand system developed by Percec and co‐workers consisting of [Ni(dppp)Cl 2 ] (dppp=1,3‐bis(diphenylphosphino)propane) and dppf as the co‐ligand turned out to be very efficient for the borylation of aryl chlorides –. Furthermore, this system, as well as [Ni(dppp)Cl 2 ] with PPh 3 (triphenylphosphine) as the additional ligand, turned out to be effective catalysts for the borylation of aryl iodides, bromides, and chlorides bearing electron‐rich and electron‐deficient ortho ‐substituents in toluene at 100 °C . These borylation reactions involved the use of in situ prepared HBneop as the boron source formed by adding BH 3 DMS (DMS=dimethylsulfide) to a toluene solution of neopentylglycol, as well as NEt 3 as an additive, which has to be freshly distilled from CaH 2 for a satisfying catalytic conversion –.…”

Scope of the Palladium-Catalyzed Aryl Borylation Utilizing Bis-Boronic Acid

“…12–17 Although these methods supply the requisite boron species in reasonable yields, all current methods result in the formation of boronate esters, and require additional steps (acid hydrolysis, 18–21 oxidation, 22–25 or reduction 26 ) to reveal the boronic acid if it is the required boron partner. Of greatest importance when applying these methods is the choice of borylating reagent.…”

Pinacol Boronates by Direct Arene Borylation with Borenium Cations

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Aryl boronate esters are essential synthetic building blocks, their ubiquity arising from ease of handling combined with high efficacy in CÀX (X = C, N, O) bond-forming reactions. [1][2][3][4][5][6][7] Recent alternative approaches avoiding haloarenes include: [4+2] cycloadditions, [8] aryl-CH deprotonation, [9,10] diazonium ions, [11] and direct arene borylation with sterically hindered iridium catalysts. [1][2][3][4][5][6][7] Recent alternative approaches avoiding haloarenes include: [4+2] cycloadditions, [8] aryl-CH deprotonation, [9,10] diazonium ions, [11] and direct arene borylation with sterically hindered iridium catalysts.

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“…[1] Aryl boronate esters are commonly synthesized from arenes by a multistep process involving haloarene intermediates and either stoichiometric hard organometallic reagents or metalcatalyzed cross-coupling (e.g., Cu, Ni, Co, or Pd). [1][2][3][4][5][6][7] Recent alternative approaches avoiding haloarenes include: [4+2] cycloadditions, [8] aryl-CH deprotonation, [9,10] diazonium ions, [11] and direct arene borylation with sterically hindered iridium catalysts. [12][13][14] The latter represents a considerable advance, being highly generic and proceeding in one step from the parent aryl CH.…”