Tandem Chemoselective Suzuki–Miyaura Cross‐Coupling Enabled by Nucleophile Speciation Control

Control of boronic acid speciation is presented as a strategy to achieve nucleophile chemoselectivity in the Suzuki–Miyaura reaction. Combined with simultaneous control of oxidative addition and transmetalation, this enables chemoselective formation of two C? C bonds in a single operation, providing a method for the rapid preparation of highly functionalized carbogenic frameworks.     

Influence of the Base on Pd@MIL‐101‐NH2(Cr) as Catalyst for the Suzuki–Miyaura Cross‐Coupling Reaction

The chemical stability of metal–organic frameworks (MOFs) is a major factor preventing their use in industrial processes. Herein, it is shown that judicious choice of the base for the Suzuki–Miyaura cross‐coupling reaction can avoid decomposition of the MOF catalyst Pd@MIL‐101‐NH₂(Cr). Four bases were compared for the reaction: K₂CO₃, KF, Cs₂CO₃ and CsF. The carbonates were the most active and achieved excellent yields in shorter reaction times than the fluorides. However, powder XRD and N₂ sorption measurements showed that the MOF catalyst was degraded when carbonates were used but remained crystalline and porous with the fluorides. XANES measurements revealed that the trimeric chromium cluster of Pd@MIL‐101‐NH₂(Cr) is still present in the degraded MOF. In addition, the different countercations of the base significantly affected the catalytic activity of the material. TEM revealed that after several catalytic runs many of the Pd nanoparticles (NPs) had migrated to the external surface of the MOF particles and formed larger aggregates. The Pd NPs were larger after catalysis with caesium bases compared to potassium bases.     

Cavity‐Shaped Ligands: Calix[4]arene‐Based Monophosphanes for Fast Suzuki–Miyaura Cross‐Coupling

Five conical calix[4]arenes that have a PPh₂ group as the sole functional group anchored at their upper rim were assessed in palladium‐catalysed cross‐coupling reactions of phenylboronic acid with aryl halides (dioxane, 100 °C, NaH). With arylbromides, remarkably high activities were obtained with the catalytic systems remaining stable for several days. The performance of the ligands is comparable to a Buchwald‐type triarylphosphane, namely, (2′‐methyl[1,1′‐biphenyl]‐2‐yl)diphenylphosphane, which in contrast to the calixarenyl phosphanes tested may display chelating behaviour in solution. With the fastest ligand, 5‐diphenylphosphanyl‐25,26,27,28‐tetra(p‐methoxy)benzyloxy‐calix[4]arene ( 8 ), the reaction turnover frequency for the arylation of 4‐bromotoluene was 321 000 versus 214 000 mol(ArBr).mol(Pd)^?1. h^?1 for the reference ligand. The calixarene ligands were also efficient in Suzuki cross‐coupling reactions with aryl chlorides. Thus, by using 1 mol % of [Pd(OAc)₂] associated with one of the phosphanes, full conversion of the deactivated arenes 4‐chloroanisole and 4‐chlorotoluene was observed after 16 h. The high performance of the calixarenyl–phosphanes in Suzuki–Miyaura coupling of aryl bromides possibly relies on their ability to stabilise a monoligand [Pd⁰L(ArBr)] species through supramolecular binding of the Pd‐bound arene inside the calixarene cavity.     

Speciation Control During Suzuki–Miyaura Cross‐Coupling of Haloaryl and Haloalkenyl MIDA Boronic Esters

Boronic acid solution speciation can be controlled during the Suzuki–Miyaura cross‐coupling of haloaryl N‐methyliminodiacetic acid (MIDA) boronic esters to enable the formal homologation of boronic acid derivatives. The reaction is contingent upon control of the basic biphase and is thermodynamically driven: temperature control provides highly chemoselective access to either BMIDA adducts at room temperature or boronic acid pinacol ester (BPin) products at elevated temperature. Control experiments and solubility analyses have provided some insight into the mechanistic operation of the formal homologation process.     

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.

     

Click Ionic Liquids: A Family of Promising Tunable Solvents and Application in Suzuki–Miyaura Cross‐Coupling

A series of click ionic salts 4 a – 4 n was prepared through click reaction of organic azides with alkyne‐functionalized imidazolium or 2‐methylimidazolium salts, followed by metathesis with lithium bis(trifluoromethanesulfonyl)amide or potassium hexafluorophosphate. All salts were characterized by IR, NMR, TGA, and DSC, and most of them can be classified as ionic liquids. Their steric and electronic properties can be easily tuned and modified through variation of the aromatic or aliphatic substituents at the imidazolium and/or triazolyl rings. The effect of anions and substituents at the two rings on the physicochemical properties was investigated. The charge and orbital distributions based on the optimized structures of cations in the salts were calculated. Reaction of 4 a with PdCl₂ produced mononuclear click complex 4 a‐Pd , the structure of which was confirmed by single‐crystal X‐ray diffraction analysis. Suzuki–Miyaura cross‐coupling shows good catalytic stability and high recyclability in the presence of PdCl₂ in 4 a . TEM and XPS analyses show formation of palladium nanoparticles after the reaction. The palladium NPs in 4 a are immobilized by the synergetic effect of coordination and electrostatic interactions with 1,2,3‐triazolyl and imidazolium, respectively.     

PEPPSI‐Type Palladium Complexes Containing Basic 1,2,3‐Triazolylidene Ligands and Their Role in Suzuki–Miyaura Catalysis

A series of PEPPSI‐type palladium(II) complexes was synthesized that contain 3‐chloropyridine as an easily removable ligand and a triazolylidene as a strongly donating mesoionic spectator ligand. Catalytic tests in Suzuki–Miyaura cross‐coupling reactions revealed the activity of these complexes towards aryl bromides and aryl chlorides at moderate temperatures (50 °C). However, the impact of steric shielding was the inverse of that observed with related normal Nheterocyclic carbenes (imidazol‐2‐ylidenes) and sterically congested mesityl substituents induced lower activity than small alkyl groups. Mechanistic investigations, including mercury poisoning experiments, TEM analyses, and ESI mass spectrometry, provide evidence for ligand dissociation and the formation of nanoparticles as a catalyst resting state. These heterogeneous particles provide a reservoir for soluble palladium atoms or clusters as operationally homogeneous catalysts for the arylation of aryl halides. Clearly, the substitution of a normal N‐heterocyclic carbene for a more basic triazolylidene ligand in the precatalyst has a profound impact on the mode of action of the catalytic system.     

Palladium‐Catalyzed Chemoselective Allylic Substitution,Suzuki–Miyaura Cross‐Coupling,and Allene Formation of Bifunctional 2‐B(pin)‐Substituted Allylic Acetate Derivatives

A formidable challenge at the forefront of organic synthesis is the control of chemoselectivity to enable the selective formation of diverse structural motifs from a readily available substrate class. Presented herein is a detailed study of chemoselectivity with palladium‐based phosphane catalysts and readily available 2‐B(pin)‐substituted allylic acetates, benzoates, and carbonates. Depending on the choice of reagents, catalysts, and reaction conditions, 2‐B(pin)‐substituted allylic acetates and derivatives can be steered into one of three reaction manifolds: allylic substitution, Suzuki–Miyaura cross‐coupling, or elimination to form allenes, all with excellent chemoselectivity. Studies on the chemoselectivity of Pd catalysts in their reactivity with boron‐bearing allylic acetate derivatives led to the development of diverse and practical reactions with potential utility in synthetic organic chemistry.     

Ligand‐Promoted Oxidative Cross‐Coupling of Aryl Boronic Acids and Aryl Silanes by Palladium Catalysis

The first cross‐coupling reaction between aryl silanes and aryl boronic acids is described. This transformation represents one of the very few examples of coupling reactions between two nucleophilic organometallic reagents and provides a new method for the formation of biaryl compounds. The successful development of this reaction was enabled by the use of commercially available 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP) as the ligand. A small amount of BINAP (3 mol %) was sufficient to suppress the formation of the homocoupling products, and the reaction yielded the cross‐coupling products with high selectivity under mild conditions, even when the ratio of the two coupling partners was 1:1.     

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.

     

Palladium supported on silica–chitosan hybrid material (Pd‐CS@SiO2) for Suzuki–Miyaura and Mizoroki–Heck cross‐coupling reactions

Palladium supported on silica–chitosan hybrid material was prepared and characterized using thermogravimetric and differential thermogravimetric analyses, scanning electron microscopy, and Fourier transform infrared, energy‐dispersive X‐ray and X‐ray photoelectron spectroscopies. The prepared Pd‐CS@SiO₂ catalyst (1 mol%) was used for the Suzuki–Miyaura cross‐coupling reaction of various aryl halides and arylboronic acids in 95% ethanol at 80 °C and the Mizoroki–Heck reaction in dimethylformamide at 110 °C using K₂CO₃ as a base. The developed catalyst is well suitable for the 3R approach (recoverable, robust, recyclable) for cross‐coupling reactions without appreciable loss of its activity. Copyright © 2015 John Wiley & Sons, Ltd.     

A Retrospective on the Design and Synthesis of Novel Molecules through a Strategic Consideration of Metathesis and Suzuki–Miyaura Cross‐Coupling

Synergy in synthesis : Strategic consideration of metathesis and Suzuki–Miyaura (SM) cross‐coupling for C? C bond‐formation processes has opened up new and “green” synthetic routes to various complex targets. The use of this synergistic combination for the synthesis of supramolecular ligands, polyaromatic compounds, and complex natural products is covered in this Focus Review.

     

Arylhydrazones Derivatives Containing a Benzothiazole Moiety,Efficient Ligands in the Palladium‐Catalyzed Mizoroki–Heck and Suzuki–Miyaura Cross‐coupling Reactions under IR Irradiation

A simple arylhydrazone containing the benzothiazole moiety which may be used as an efficient ligand in the palladium‐catalyzed Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions, under infrared irradiation as an alternative source of energy, is presented. The reactions proceeded with extremely high efficiency under mild conditions and produced very good yields.     

Tripod Immobilization of Triphenylphosphane on a Silica‐Gel Surface to Enable Selective Mono‐Ligation to Palladium: Application to Suzuki–Miyaura Cross‐Coupling Reactions with Chloroarenes

A silica‐supported triphenylphosphane (Silica‐3p‐TPP) with a Ph₃P‐type core, immobilized on a silica surface, was synthesized and characterized by nitrogen‐absorption measurements and solid‐state NMR spectroscopy. The tripodal immobilization constrains the mobility of the phosphane molecule and causes the lone pair on the phosphorus atom to face in the direction perpendicular to the support, resulting in the selective formation of a 1:1 metal–phosphane species that is free from unfavorable steric repulsions caused by the silica surface. Heterogeneous Pd catalysts created in this manner enabled room‐temperature Suzuki–Miyaura cross‐coupling reactions with unactivated chloroarenes, despite the moderate electronic and steric nature of the Ph₃P‐based ligands. These catalysts also showed potential in reactions with more challenging substrates under mild conditions. Tripodally immobilized and well‐dispersed phosphanes on the silica surface were crucial for high catalytic activity.     

A Triptycene‐Based Microporous Organic Polymer Bearing Tridentate Ligands and Its Application in Suzuki–Miyaura Cross‐Coupling Reaction

A triptycene‐based microporous organic polymer (MOP) in which 2,6‐bis(benzimidazol‐2‐yl)pyridine (bbp) is incorporated as linkage and coordination site is designed and synthesized. Pd(II) ions are further immobilized in this MOP through the coordination interactions between Pd(II) ion and nitrogen atoms of bbp. The resulting material shows high stability and exhibits excellent heterogeneously catalytic activity for the Suzuki–Miyaura cross‐coupling reaction. Its high efficiency can be maintained after being reused for a number of cycles.