A Facile Route to Aryl Boronates: Room‐Temperature,Copper‐Catalyzed Borylation of Aryl Halides with Alkoxy Diboron Reagents

A simple but effective copper‐catalyzed borylation of aryl halides, including electron‐rich and sterically hindered aryl bromides, with alkoxy diboron reagents occurs under mild conditions (see scheme). Preliminary DFT studies of the mechanism suggest that σ‐bond metathesis between a copper–boryl intermediate and the aryl halide generates the aryl boronate product.

     

Zinc‐Catalyzed Dual C–X and C–H Borylation of Aryl Halides

A zinc‐catalyzed combined C? X and C? H borylation of aryl halides using B₂pin₂ (pin=OCMe₂CMe₂O) to produce the corresponding 1,2‐diborylarenes under mild conditions was developed. Catalytic C? H bond activation occurs ortho to the halide groups if such a site is available or meta to the halide if the ortho position is already substituted. This method thus represents a novel use of a group XII catalyst for C? H borylation. This transformation does not proceed via a free aryne intermediate, but a radical process seems to be involved.     

The Selective Cross‐Coupling of Secondary Alkyl Zinc Reagents to Five‐Membered‐Ring Heterocycles Using Pd‐PEPPSI‐IHeptCl

The ability to cross‐couple secondary alkyl centers is fraught with a number of problems, including difficult reductive elimination, which often leads to β‐hydride elimination. Whereas catalysts have been reported that provide decent selectivity for the expected (non‐rearranged) cross‐coupled product with aryl or heteroaryl oxidative‐addition partners, none have shown reliable selectivity with five‐membered‐ring heterocycles. In this report, a new, rationally designed catalyst, Pd‐PEPPSI‐IHept^Cl, is demonstrated to be effective in selective cross‐coupling reactions with secondary alkyl reagents across an impressive variety of furans, thiophenes, and benzo‐fused derivatives (e.g., indoles, benzofurans), in most instances producing clean products with minimal, if any, migratory insertion for the first time.     

Organotrifluoroborates and Monocoordinated Palladium Complexes as Catalysts—A Perfect Combination for Suzuki–Miyaura Coupling

Monocoordinated palladium catalysts derived from sterically hindered, electron‐rich phosphines or N‐heterocyclic carbenes have revolutionized the Suzuki–Miyaura coupling reaction. The emergence of organotrifluoroborates has provided important new perspectives for the organoboron component of these reactions. In combination, these two components prove to be extraordinarily powerful partners for cross‐coupling reactions.     

Nickel‐Catalyzed Cross‐Coupling of Non‐activated and Functionalized Alkyl Halides with Alkyl Grignard Reagents

Reacting in the 'Ni'ck of time : The title reaction is realized by using an isolated Ni^II complex ( 1 ). The catalysis tolerates a wide range of important functional groups that are often incompatible with Grignard reagents in cross‐coupling reactions.

     

HandaPhos: A General Ligand Enabling Sustainable ppm Levels of Palladium‐Catalyzed Cross‐Couplings in Water at Room Temperature

The new monophosphine ligand HandaPhos has been identified such that when complexed in a 1:1 ratio with Pd(OAc)₂, enables Pd‐catalyzed cross‐couplings to be run using ≤1000 ppm of this pre‐catalyst. Applications to Suzuki–Miyaura reactions involving highly funtionalized reaction partners are demonstrated, all run using environmentally benign nanoreactors in water at ambient temperatures. Comparisons with existing state‐of‐the‐art ligands and catalysts are discussed herein.     

Devising Boron Reagents for Orthogonal Functionalization through Suzuki–Miyaura Cross‐Coupling

Seeing the sites : The Suzuki–Miyaura reaction of substrates containing multiple coupling sites has been performed in a directed manner through the reactivity modulation of the boron moiety (see scheme). Several other strategies are also discussed.

     

A comparative study of hydroxyl‐ and carboxylate‐functionalized imidazolium and benzimidazolium salts as precursors for N‐heterocyclic carbene ligands

The preparation of imidazolium and benzimidazolium salts with hydroxyl or carboxylate functions has been achieved using straightforward synthetic pathways. These salts in combination with palladium(II) acetate give active catalytic systems for Suzuki reaction. A comparative study has been performed, which has revealed that both the heterocycle and the functional group are important for the catalytic activity and stability of the catalyst. Copyright © 2015 John Wiley & Sons, Ltd.     

Oxygen‐Promoted Suzuki–Miyaura Reaction for Efficient Construction of Biaryls

As one of the most powerful and versatile methods for the construction of carbon–carbon bonds, the Suzuki–Miyaura cross‐coupling reaction has attracted great attention over the past three decades. In recent years, a huge amount of interest has been focused on the development of ligand‐free Suzuki–Miyaura reaction systems, which have the advantages of low cost, mild reaction conditions, and easy operation. So far, a number of ligand‐free Suzuki–Miyaura reaction systems have been developed by using simple palladium salts, nanopalladium, or supported palladium catalysts. In this account, we will review our recent research on the oxygen‐promoted ligand‐free Suzuki–Miyaura reaction. Interestingly, the oxygen‐promoting effect has been observed in different reaction media, including polyethylene glycol, organic/water mixed solvents and pure water. The oxygen‐promoted reaction systems demonstrate high efficiency for the construction of biaryls.

     

Modular Synthesis of Triarylmethanes through Palladium‐Catalyzed Sequential Arylation of Methyl Phenyl Sulfone

Triarylmethanes, which are valuable structures in materials, sensing and pharmaceuticals, have been synthesized starting from methyl phenyl sulfone as an inexpensive and readily available template. The three aryl groups were installed through two sequential palladium‐catalyzed C? H arylation reactions, followed by an arylative desulfonation. This method provides a new synthetic approach to multisubstituted triarylmethanes using readily available haloarenes and aryl boronic acids, and is also valuable for the preparation of unexplored triarylmethane‐based materials and pharmaceuticals.     

Comparison of dppf‐Supported Nickel Precatalysts for the Suzuki–Miyaura Reaction: The Observation and Activity of Nickel(I)

Ni‐based precatalysts for the Suzuki–Miyaura reaction have potential chemical and economic advantages compared to commonly used Pd systems. Here, we compare Ni precatalysts for the Suzuki–Miyaura reaction supported by the dppf ligand in 3 oxidation states, 0, I and II. Surprisingly, at 80 °C they give similar catalytic activity, with all systems generating significant amounts of Ni^I during the reaction. At room temperature a readily accessible bench‐stable Ni^II precatalyst is highly active and can couple synthetically important heterocyclic substrates. Our work conclusively establishes that Ni^I species are relevant in reactions typically proposed to involve exclusively Ni⁰ and Ni^II complexes.     

Well‐dispersed N‐heterocyclic carbene–palladium complex anchored onto poly(acrylic acid)/poly(vinyl alcohol) nanofibers: Novel,superior and ecofriendly nanocatalyst for the Suzuki–Miyaura cross‐coupling reaction

Polymeric nanocomposite@Pd is one of the crown jewels for the catalysis of cross‐coupling reactions. This Pd nanocomposite on various polymeric supports has been well established to catalyze cross‐coupling reactions, but its preparation supported on the surface of nanofibers has been largely overlooked. Herein, we report the preparation of a poly(acrylic acid) (PAA)/poly(vinyl alcohol) (PVA) nanofiber‐supported N‐heterocyclic carbene–Pd complex. The first step involves the preparation of PAA/PVA nanofibers using the electrospinning process. The second step comprises the reaction of water‐soluble poly(ethylene glycol)‐imidazole with modified PAA/PVA nanofibers followed by introduction of PdCl₂ to achieve successfully the desired nanocomposite. The catalytic activity of this nanocomposite was examined in the expeditious synthesis of biaryl compounds using the Suzuki–Miyaura cross‐coupling reaction under mild reaction conditions. The composite offers multiple features such as good hydrophilic properties, high surface area, admirable potential in repeatability tests and being recyclable for several runs without significant loss in its activity under the optimum reaction conditions. Our results showed the superior applicability of this novel nanocatalyst in terms of conversion reaction, yields and turnover frequencies. The structure of the catalyst was characterized using a variety of techniques.     

Triazole‐Functionalized N‐Heterocyclic Carbene Complexes of Palladium and Platinum and Efficient Aqueous Suzuki–Miyaura Coupling Reaction

Imidazolium salts bearing triazole groups are synthesized via a copper catalyzed click reaction, and the silver, palladium, and platinum complexes of their N‐heterocyclic carbenes are studied. [Ag₄(L1)₄](PF₆)₄, [Pd(L1)Cl](PF₆), [Pt(L1)Cl](PF₆) (L1=3‐((1‐benzyl‐1H‐1,2,3‐triazol‐4‐yl)methyl)‐1‐(pyrimidin‐2‐yl)‐1H‐imidazolylidene), [Pd₂(L2)₂Cl₂](PF₆)₂, and [Pd(L2)₂](PF₆)₂ (L2=1‐butyl‐3‐((1‐(pyridin‐2‐yl)‐1H‐1,2,3‐triazol‐4‐yl)methyl)imidazolylidene) have been synthesized and fully characterized by NMR, elemental analysis, and X‐ray crystallography. The silver complex [Ag₄(L1)₄](PF₆)₄ consists of a Ag₄ zigzag chain. The complexes [Pd(L1)Cl](PF₆) and [Pt(L1)Cl](PF₆), containing a nonsymmetrical NCN ′ pincer ligand, are square planar with a chloride trans to the carbene donor. [Pd₂(L2)₂Cl₂](PF₆)₂ consists of two palladium centers with CN₂Cl coordination mode, whereas the palladium in [Pd(L2)₂](PF₆)₂ is surrounded by two carbene and two triazole groups with two uncoordinated pyridines. The palladium compounds are highly active for Suzuki–Miyaura cross coupling reactions of aryl bromides and 1,1‐dibromo‐1‐alkenes in neat water under an air atmosphere.     

Expedient Iron‐Catalyzed Coupling of Alkyl,Benzyl and Allyl Halides with Arylboronic Esters

While attractive, the iron‐catalyzed coupling of arylboron reagents with alkyl halides typically requires expensive or synthetically challenging diphosphine ligands. Herein, we show that primary and secondary alkyl bromides and chlorides, as well as benzyl and allyl halides, can be coupled with arylboronic esters, activated with alkyllithium reagents, by using very simple iron‐based catalysts. The catalysts used were either adducts of inexpensive and widely available diphosphines or, in a large number of cases, simply [Fe(acac)₃] with no added co‐ ligands. In the former case, preliminary mechanistic studies highlight the likely involvement of iron(I)–phosphine intermediates.