Studies on Suzuki‐Miyaura Reactions Catalyzed by Ferrocenyl or Cobaltocenyl Phosphines Ligated Palladium Complexes

DFT studies on several dppf ‐ and dppc ‐derived bidentate phosphines ligated palladium complexes catalyzed Suzuki‐Miyaura coupling reactions were pursued. The catalytic reactions employing ligands, having two phosphine biting sites on different cyclpentadienyl or cyclobutadiene rings, such as 1,1'‐dmpf or 1,1' ‐dmpc, have been verified to be energetically more favorable than those on the same ring provided that tetra‐coordinated palladium conformations for all transition states and intermediates are maintained. Apart from the purpose of storage, the application of phosphinous acid (R₂P(OH)) in Suzuki‐Miyaura reaction is inferior to tertiary phosphine (R₃P).     

1‐(α‐Aminobenzyl)‐2‐naphthol as phosphine‐free ligand for Pd‐catalyzed Suzuki and one‐pot Wittig‐Suzuki reaction

Air stable and easily accessible, 1‐(α‐aminobenzyl)‐2‐naphthols are used as efficient phosphine‐free ligands in palladium‐catalyzed Suzuki reaction for a variety of substrates under conventional heating as well as ultrasonic conditions. Multi‐brominated aromatic substrates were successfully converted to corresponding arylated moieties with good conversion and selectivity. A novel one‐pot two‐step cascade reaction strategy involving Wittig and Suzuki reactions is developed for efficient synthesis of 4‐styryl biphenyls (C₆‐C₂‐C₆‐C₆ unit). Copyright © 2012 John Wiley & Sons, Ltd.     

Immobilized Pd on (S)‐methyl histidinate‐modified multi‐walled carbon nanotubes: a powerful and recyclable catalyst for Mizoroki–Heck and Suzuki–Miyaura C–C cross‐coupling reactions in green solvents and under mild conditions

A stable and powerful heterogeneous palladium catalyst was synthesized using immobilized palladium on (S)‐methyl histidinate bonded onto the surface of multi‐walled carbon nanotubes. The catalyst was characterized using a combination of Fourier transform infrared and X‐ray photoelectron spectroscopies, transmission electron microscopy, X‐ray powder diffraction and inductively coupled plasma, thermogravimetric and elemental analyses. This new air‐ and moisture‐stable phosphine‐free palladium catalyst was found to be highly active and reusable in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions in poly(ethylene glycol) and aqueous ethanol as green solvents using an extremely small amount of palladium under mild conditions. Copyright © 2016 John Wiley & Sons, Ltd.     

Enantiospecific Synthesis of ortho‐Substituted 1,1‐Diarylalkanes by a 1,2‐Metalate Rearrangement/anti‐SN2′ Elimination/Rearomatizing Allylic Suzuki–Miyaura Reaction Sequence

The one‐pot sequential coupling of benzylamines, boronic esters, and aryl iodides has been investigated. In the presence of an N‐activator, the boronate complex formed from an ortho‐lithiated benzylamine and a boronic ester undergoes stereospecific 1,2‐metalate rearrangement/anti‐S_N2′ elimination to form a dearomatized tertiary boronic ester. Treatment with an aryl iodide under palladium catalysis leads to rearomatizing γ‐selective allylic Suzuki–Miyaura cross‐coupling to generate 1,1‐diarylalkanes. When enantioenriched α‐substituted benzylamines are employed, the corresponding 1,1‐diarylalkanes are formed with high stereospecificity.     

The Development of Bulky Palladium NHC Complexes for the Most-Challenging Cross-Coupling Reactions

Palladium‐catalyzed cross‐coupling reactions enable organic chemists to form C? C bonds in targeted positions and under mild conditions. Although phosphine ligands have been intensively researched, in the search for even better cross‐coupling catalysts attention has recently turned to the use of N‐heterocyclic carbene (NHC) ligands, which form a strong bond to the palladium center. PEPPSI (pyridine‐enhanced precatalyst preparation, stabilization, and initiation) palladium precatalysts with bulky NHC ligands have established themselves as successful alternatives to palladium phosphine complexes. This Review shows the success of these species in Suzuki–Miyaura, Negishi, and Stille–Migita cross‐couplings as well as in amination and sulfination reactions.     

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.     

Chemoselective one‐pot synthesis of terphenyl derivatives by sequential directed C―H functionalization–Suzuki coupling

A simple and efficient route for the preparation of terphenyl derivatives via palladium‐catalyzed sequential directed C―H arylation/Suzuki–Miyaura cross‐coupling in ‘one‐pot’ has been developed. 4,4′‐(Cyclohexane‐1,1‐diyl)diphenol is an essential ligand. This reaction can tolerate a series of functional groups and provides the terphenyl derivatives in moderate to good yield. Copyright © 2014 John Wiley & Sons, Ltd.     

Tris[tri(2‐thienyl)phosphine]palladium as the catalyst precursor for thiophene‐based Suzuki‐Miyaura crosscoupling and polycondensation

Zero‐valent palladium complex, Pd(PTh₃)₃, with three tri(2‐thienyl)phosphine ligands was prepared and characterized. Pd(PTh₃)₃ is superior to Pd(PPh₃)₄ in catalyzing Suzuki‐Miyaura coupling and polymerization of thiophene‐based derivatives. The Suzuki polycondensation of 3‐hexyl‐5‐iodothiophene‐2‐boronic pinacol ester with Pd(PTh₃)₃ as the catalyst precursor afforded high‐molecular‐weight P3HT with high regularity and yield. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4556–4563, 2008     

An improved preparation of mesoporous silica‐supported Pd as sustainable catalysts for phosphine‐free Suzuki–Miyaura and Heck coupling reactions

An improved and eco‐friendly procedure has been developed to generate mesoporous silica‐supported palladium nanoparticles (SiO₂@PdNP) that could be used as a sustainable heterogeneous Pd catalyst for phosphine‐free Suzuki–Miyaura and Heck coupling reactions with excellent turnover number and turnover frequency. The presence of Pd on the silica surface was detected by X‐ray diffraction and the structural morphology of SiO₂@PdNP was obtained by transmission electron microscopy. The heterogeneous catalytic system is recyclable and leaching of the metal after the reaction is not apparently observed. Copyright © 2013 John Wiley & Sons, Ltd.     

Imidazolin‐2‐ylidenaminophosphines as Highly Electron‐Rich Ligands for Transition‐Metal Catalysts

A variety of chemical transformations benefit from the use of strong electron‐donating ancillary ligands, such as alkylphosphines or N‐heterocyclic carbenes when electron‐rich metal centers are required. Herein, we describe a facile and highly modular access to monodentate and bidentate imidazolin‐2‐ylidenamino‐substituted phosphines. Evaluation of the phosphine’s electronic properties substantiate that the formal replacement of alkyl or aryl groups by imidazolin‐2‐ylidenamino groups dramatically enhance their donor ability beyond that of alkylphosphines and even N‐heterocyclic carbenes. The new phosphines have been coordinated onto palladium(II) centers, and the beneficial effect of the novel substitution patterns has been explored by using the corresponding complexes in the palladium‐catalyzed Suzuki–Miyaura cross‐coupling reaction of non‐activated aryl chloride substrates.     

Preparations of Saturated N‐P‐N Type Secondary Phosphine Oxides and their Applications in Cross‐Coupling Reactions

A series of cyclohexane‐1,2‐diamine ( 3a – 3d ) and benzene‐1,2‐diamine derivatives ( 3e – 3h ) were pre‐ pared. Followed by hydrolysis, the reaction of 3a – 3c with PCl₃ successfully led to the formation of cor‐ responding metastable saturated heteroatom‐substituted secondary phosphine oxides (HASPO 4a – 4c ), a tautomer of the saturated heteroatom‐substituted phosphinous acid (HAPA). Whereas ambient‐stable diamine‐coordinated palladium complexes were obtained, HAPA‐coordinated palladium complexes were not successfully synthesized. The molecular structures of HASPO 4c , Pd(OAc)₂(3a) , PdBr₂(3b) and Pd(OAc)₂(3c) and [Cu(NO₃)(3d)⁺][NO₃ ^? ] were determined by single‐crystal X‐ray diffraction method. Catalysis of in‐situ Suzuki‐Miyaura cross‐coupling reactions for aryl bromides and phenylboronic acid using diamine 3a as ancillary ligand showed that the optimized reaction condition at 60 °C is the combination of 2 mmol % 3a /3.0 mmol KOH/1.0 mL 1,4‐dioxane/1 mmol % Pd(OAc)₂. Moreover, moderate reactivity was observed when using aryl chlorides as substrates (supporting infor‐ mation). When diamine 3d was employed in Heck reaction, good tolerance of functional groups of aryl bromides were observed while using 4‐bromoanisole and styrene as substrates. The optimized condi‐ tion for Heck reaction at 100 °C is 3 mmol % 3d /3.0 mmol CsF/1.0 mL toluene/3 mmol % Pd(OAc)₂. In general, cyclohexane‐1,2‐diamine derivatives exhibited better catalytic properties than those of benzene‐1,2‐diamines.     

Preparation of Phosphinated Polymer‐Incarcerated Palladium and Its Application to C?N and C?C Bond‐Forming Reactions

Phosphinated polymer‐incarcerated (PI) Pd catalysts were prepared by immobilization of palladium with phosphinated polymers by using the PI method. The phosphinated PI Pd catalysts showed good catalytic activity without externally added phosphine ligands in the amination of aryl halides for C N bond‐forming reactions, as well as in Suzuki–Miyaura and Sonogashira coupling. No leaching of palladium from the immobilized Pd was observed by fluorescence X‐ray analysis. Furthermore, it was found that immobilization of Pd by the PI process facilitated the suppression of poisoning of the metal by amines. These effects can be ascribed to stabilization of the catalyst by both the phosphine moieties and the benzene rings in the swollen polymer support. The phosphinated PI Pd catalysts could also be recovered by simple filtration and reused several times without leaching of palladium in both the amination and Suzuki–Miyaura coupling reactions.     

A highly selective synthesis of 1‐substituted (E)‐buta‐1,3‐dienes with 4,4,5,5‐tetramethyl‐2‐vinyl‐1,3,2‐dioxaborolane as building block

Highly selective synthesis of 1‐substituted (E)‐buta‐1,3‐dienes via palladium‐catalyzed Suzuki–Miyaura cross‐coupling of (E)‐alkenyl iodides with 4,4,5,5‐tetramethyl‐2‐vinyl‐1,3,2‐dioxaborolane ( 1 ) is reported. The vinylboronate pinacol ester ( 1 ) acts as a vinyl building block to show high chemoselectivity for the Suzuki–Miyaura pathway versus Heck coupling in the presence of biphasic conditions (Pd(PPh₃)₄, aqueous K₂CO₃, toluene and ethanol). Copyright © 2014 John Wiley & Sons, Ltd.     

Carboxymethylcellulose‐supported palladium nanoparticles generated in situ from palladium(II) carboxymethylcellulose as an efficient and reusable catalyst for ligand‐ and base‐free Heck–Matsuda and Suzuki–Miyaura couplings

A novel palladium(II) carboxymethylcellulose (CMC‐Pd^II) was prepared by direct metathesis from sodium carboxymethylcellulose and PdCl₂ in aqueous solution. Its catalytic activities were explored for Heck–Matsuda reactions of aryldiazonium tetrafluoroborate with olefins, and Suzuki–Miyaura couplings of aryldiazonium tetrafluoroborate with arylboronic acid. Both reactions proceeded at room temperature in water or aqueous ethanol media without the presence of any ligand or base, to provide the corresponding cross‐coupling products in good to excellent yields under atmospheric conditions. The CMC‐Pd^II and carboxymethylcellulose‐supported palladium nanoparticles (CMC‐Pd⁰) formed in situ in the reactions were characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, inductively coupled plasma atomic emission spectrometry, and scanning and transmission electron microscopies. The homogeneous nature of the CMC‐Pd⁰ catalyst was confirmed via Hg(0) and CS₂ poisoning tests. Moreover, the CMC‐Pd⁰ catalyst could be conveniently recovered by simple filtration and reused for at least ten cycles in Suzuki–Miyaura reactions without apparently losing its catalytic activity. The catalytic system not only overcomes the basic drawbacks of homogeneous catalyst recovery and reuse but also avoids the need to fabricate palladium nanoparticles in advance. Copyright © 2015 John Wiley & Sons, Ltd.     

Alcoholic solvent‐assisted ligand‐free room temperature Suzuki–Miyaura cross‐coupling reaction

We have observed the enhancing effect of alcoholic solvents in palladium‐catalysed ligand‐free Suzuki–Miyaura reactions. No extra additives or ligands are required for the Suzuki–Miyaura reaction of aryl bromides with arylboronic acids when we carried out the reaction in alcoholic or aqueous alcoholic solvents. Moreover, ethanol or aqueous ethanol is found to be a very good solvent for the Suzuki–Miyaura reaction involving electronically diverse aryl bromides and arylboronic acids under mild and ligand‐free conditions with low catalyst loading. It is observed from Hg(0) poisoning tests that the in situ generated palladium(0) species is the actual catalytic species for the reaction. Copyright © 2015 John Wiley & Sons, Ltd.     

Catalytic activities of NHC‐PdCl2 species based on functionalized tetradentate imidazolium salt in three types of C‐C coupling reactions

A functionalized tetradentate imidazolium salt 9,10‐bis{di[2′‐(N‐ethylimidazolium‐1‐yl)ethyl]aminomethyl}anthracene tetrakis(hexafluorophosphate) ( 1 ) has been synthesized and characterized. The catalytic activity of the NHC‐PdCl₂ species formed by compound 1 and PdCl₂ was tested in Suzuki‐Miyaura, Heck‐Mizoroki and Sonogashira reactions. The results showed that this catalytic system was effective for above three types of C‐C coupling reactions.     

Magnetically‐recoverable Schiff Base Complex of Pd (II) Immobilized on Fe3O4@SiO2 Nanoparticles: An Efficient Catalyst for Mizoroki‐Heck and Suzuki‐Miyaura Coupling Reactions

The activity of Pd(II)‐Schiff base complex molecules grafted on the surface of Fe₃O₄@SiO₂ particles were investigated in the palladium‐catalyzed coupling reactions of aryl halides with alkenes (Mizoroki‐Heck reaction) and phenylboronic acids (Suzuki‐Miyaura reaction) in the absence of phosphorous ligands. This method shows notable advantages such as heterogeneous nature of the catalyst, excellent yields, short reaction times, easy preparation, simplicity of operation, and cleaner reaction profiles. The catalyst can be separated from the reaction mixture by applying a permanent magnet externally and can be reused for several times without significant loss of activity. Also, the amount of palladium leaching has been determined by ICP analysis.     

Room temperature suzuki cross‐coupling polymerizations of aryl dihalides and aryldiboronic acid/acid esters with t‐Bu3P‐coordinated 2‐phenylaniline‐based palladacycle complex as the precatalyst

Room temperature Suzuki cross‐coupling polymerization of aryl dibromides/diiodides with aryldiboronic acids/acid esters with t‐Bu₃P‐coordinated 2‐phenylaniline‐based palladacycle complex, [2′‐(amino‐kN)[1,1′‐biphenyl]‐2‐yl‐kC]chloro(tri‐t‐butylphosphine)palladium, as a general precatalyst is described. Such room temperature Suzuki cross‐coupling polymerization is achieved by employing six equivalents or more of the base and affords polymers within an hour, with the yields and the molecular weights in general comparable to or higher than reported results that required higher reaction temperature and/or longer polymerization time. Our study provides a general catalyst system for the room temperature Suzuki cross‐coupling polymerization of aryl dibromides/diiodides with aryldiboronic acids/acid esters and paves the road for the investigation of employing other monodentate ligand‐coordinated palladacycle complexes including other electron‐rich monophosphine‐coordinated ones for room temperature cross‐coupling polymerizations. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1606–1611     

Robust and Electron‐Rich cis‐Palladium(II) Complexes with Phosphine and Carbene Ligands as Catalytic Precursors in Suzuki Coupling Reactions

A new imidazolinium ligand precursor [L²H]Cl ( 2 ) was prepared in 86 % yield. Compared with its imidazolium counterpart, [L¹H]Cl ( 1 ), 2 is very sensitive to moisture and can undergo ring‐opening reactions very readily. Palladium complexes with the ring‐opened products from imidazolinium salts were isolated and characterized by X‐ray crystallography. Theoretical studies confirmed that the imidazolinium salt has a higher propensity for the ring‐opening reaction than the imidazolium counterpart. New mixed phosphine/carbene palladium complexes, cis‐[PdCl₂(L)(PR₃)] (L=L¹ and L²; R=Ph, Cy), were successfully prepared. These complexes are highly robust as revealed by variable‐temperature NMR spectroscopic studies and thermal gravimetric analysis. The structural and electronic properties of the new complexes on varying the carbene group (imidazol‐2‐ylidene group (unsaturated carbene) vs. imidazolin‐2‐ylidene (saturated carbene)) and the phosphine group (PPh₃ vs. PCy₃) were studied in detail by X‐ray crystallography, X‐ray photoelectron spectroscopy, and theoretical calculations. The catalytic study reveals that cis‐[PdCl₂(L²)(PCy₃)] is a competent Pd^II precatalyst for Suzuki coupling reactions, in which unreactive aryl chlorides can be applied as substrates.     

双功能手性联萘酚配体在炔基锌对醛的不对称加成反应选择性能研究

单体2-溴吡啶, 2-溴-5-甲基吡啶, 2-氯-4-氟吡啶, 2-氯-3-三氟甲基吡啶分别与( R )-3,3′-二硼酸-2,2′-二甲氧基-1,1′-联萘 [( R )-2]在钯催化下, 通过Suzuki交叉耦合反应合成得到四个类似手性化合物( R )-3a-d。将它们应用到炔基锌对醛的不对称催化加成反应中,结果表明( R )-3a和( R )-3b的催化效果不好, 而( R )-3d只对脂肪醛有很好的催化效果,( R )-3c则对这类不对称催化反应均有很好的催化效果, 能给出高达95%的收率和99%的选择性结果。结果还表明所产生相应炔丙醇异构体构型为S,这与手性催化剂构型相反。