Zero-Valent Metals Accelerate the Neopentylglycolborylation of Aryl Halides Catalyzed by NiCl₂-Based Mixed-Ligand Systems

Abstract

The highly active mixed-ligand catalytic system NiCl2(dppp)/dppf combined with the reducing effect of zerovalent Zn and of other metals was used to demonstrate a method for the dramatic acceleration of the rate and for the enhancement of the yield of Ni-catalyzed neopentylglycolborylation of aryl halides. A diversity of electron-rich and electron-deficient aryl iodides, bromides, and chlorides were efficiently neopentylglycolborylated, typically in 1 h or less. This acceleration is particularly remarkable for the generally less reactive aryl bromides and chlorides and for all ortho-substituted aryl halides. By accelerating the rate of borylation and reducing its reaction time to complete conversion, pathways leading to protodeborylated or hydrodehalogenated side products have a reduced impact on the outcome of the overall reaction. Although Zn powder was the reducing agent of choice, compatibility of this technique with more readily recoverable Zn chips, as well as other metals such as Mn, Mg, Fe, Al, and Ca, has demonstrated the broad scope of this synthetic method.

Nickel-Catalyzed Borylation of Halides and Pseudohalides with Tetrahydroxydiboron [B2(OH)4]

“…The products were obtained in good yields without the use of additives as required using previously developed nickel-catalyzed borylation methods. 12e …”

“…However, the selectivities of these reactions are determined by steric and electronic effects within the aryl system, making them limited to specific substitution patterns. To overcome these limitations, Cu, 11 Ni 12 and Pd 13 -catalyzed Miyaura borylations of aryl and heteroaryl halides have been developed. Regardless of the high selectivity and functional group compatibility, these methods often require the use of bis(pinacolato) diboron (B 2 Pin 2 ), pinacolborane (HBPin), or neopentylglycolborane as a boron source, thus resulting in the initial formation of boronates.…”

“…Previously reported nickel-catalyzed borylations 12 not only utilize the aforementioned wasteful borylating reagents (e.g., B 2 Pin 2 and neopentylglycolborane), but they also require the use of additives such as zinc 12b , 12e and trimethyl(2,2,2-trifluoroethoxy)silane, 12g and proceed only at high reaction temperatures (100 – 110 °C). Additionally, although room temperature copper-catalyzed borylations have been reported, 11a , 11b the substrate scope examined, especially for heteroaryls and reactants with sensitive functional groups, has been extremely limited. Furthermore, these methods not only use inefficient B 2 Pin 2 , but they also have been employed largely for aryl iodides.…”

Synthesis and Characterization of Organic Dyes with Various Electron‐Accepting Substituents for p‐Type Dye‐Sensitized Solar Cells

“…Pure iodinated derivative 16 was obtained in 96 % yield after filtration over a short alumina column. Borylation of dyad 16 was then carried out under conditions described by Percec et al [35] to yield boronic ester 17 in 70 % yield after column chromatography. Boronic ester 17 represents a valuable building block giving the opportunity to couple different acceptors.…”

Synthesis of high performance polyacrylonitrile by RASA SET-LRP in the presence of Mg powder

“…[38][39][40][41][42][43][44][45][46][47][48] In ARGET ATRP, various reducing agents (RAs) including zero valent copper, zinc, magnesium, iron, and ascorbic acid are used to reduce transition metal complex in a high oxidation state to in a low oxidation state. [49][50][51][52] SET-LRP of methyl methacrylate catalyzed by in situ prepared Cu(0) at ambient temperature using various metallic powders including Zn(0), Ni(0), Mg(0), and Fe(0) was attempted.…”