Well‐Defined N‐Heterocyclic Carbene‐Palladium Complexes as Efficient Catalysts for Domino Sonogashira Coupling/Cyclization Reaction and C‐H bond Arylation of Benzothiazole

Well‐defined and air‐stable PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed palladium bis‐N‐heterocyclic carbene complexes have been developed for the domino Sonogashira coupling/cyclization reaction of 2‐iodophenol with a variety of terminal alkynes and C‐H bond arylation of benzothiazole with aryl iodides. The PEPPSI themed palladium complexes, 2a and 2b were synthesized in good yields from the reaction of corresponding imidazolium salts with PdCl₂ and K₂CO₃ in pyridine. The new air‐stable palladium‐NHC complexes were characterized by NMR spectroscopy, X‐ray crystallography, elemental analysis, and mass spectroscopy studies. The PEPPSI themed palladium(II) bis‐N‐heterocyclic carbene complexes 2a and 2b exhibited excellent catalytic activities for domino Sonogashira coupling/cyclization reaction of 2‐iodophenol with terminal alkynes yielding benzofuran derivatives. In addition, the palladium complexes, 2a and 2b successfully catalyzed the direct C‐H bond arylation of benzothiazole with aryl iodides as coupling partners in presence of CuI as co‐catalyst.     

Novel (N‐heterocyclic carbene)Pd(pyridine)Br2 complexes for carbonylative Sonogashira coupling reactions: Catalytic efficiency and scope for arylalkynes,alkylalkynes and dialkynes

New N,N′‐substituted imidazolium salts and their corresponding dibromidopyridine–palladium(II) complexes were successfully synthesized and characterized. Reactions of palladium bromide with the newly synthesized N,N′‐substituted imidazolium bromides ( 2a and 2b ) in pyridine afforded the corresponding new N‐heterocyclic carbene pyridine palladium(II) complexes ( 3a and 3b ) in high yields. Their single‐crystal X‐ray structures show a distorted square planar geometry with the carbene and pyridine ligands in trans position. Both complexes show a high catalytic activity in carbonylative Sonogashira coupling reactions of aryl iodides and aryl diiodides with arylalkynes, alkylalkynes and dialkynes.     

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.     

Pincer-type bis(carbene)-derived complexes of nickel(II): Synthesis, structure, and catalytic activity

Air- and moisture-stable NHC (N-heterocyclic carbene)-derived CNC-type pincer complexes of nickel(II) 4a-d were successfully synthesized, and their structures were fully characterized using X-ray crystallography and analytical and spectroscopic methods. These complexes exhibit a high catalytic activity for the Suzuki-Miyaura coupling reaction of aryl bromides and chlorides with aryl- and alkenylboronic acids, providing an array of biphenyls and stilbenes generally in high yields.     

A nickel precatalyst for efficient cross-coupling reactions of aryl tosylates with arylboronic acids: vital role of dppf

An air-stable and easy-to-handle nickel precatalyst, (9-phenanthrenyl)Ni(II)(PPh₃)₂Cl, was examined for the cross-coupling reactions of aryl tosylates with arylboronic acids. Under the optimized reaction conditions, the catalytic system tolerates a wide range of activated, neutral and deactivated substrates. The selectivity of this cross-coupling reaction towards aryl tosylates and arylboronic acids has been investigated. It is proposed that ligand 1,1′-bis(diphenylphosphino)ferrocene (dppf) plays a key role in the coupling by enforcing a cis geometry in key intermediates and the active Ni(0) species.     

Modified (NHC)Pd(allyl)Cl (NHC = N-heterocyclic carbene) complexes for room-temperature Suzuki-Miyaura and Buchwald-Hartwig reactions

A series of (NHC)Pd(R-allyl)Cl complexes [NHC: IPr = N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, SIPr = N,N'-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene; R = H, Me, gem-Me2, Ph] have been synthesized and fully characterized. When compared to (NHC)Pd(allyl)Cl, substitution at the terminal position of the allyl scaffold favors a more facile activation step. This translates into higher catalytic activity in the Suzuki-Miyaura and Buchwald-Hartwig reactions, allowing for the coupling of unactivated aryl chlorides at room temperature in minutes. In the Suzuki-Miyaura reaction, aryl triflates, bromides, and chlorides react with boronic acids using very low catalyst loading. In the N-aryl amination reaction, a wide range of substrates has been coupled efficiently; primary-, secondary-, alkyl-, or aryl-amines react in high yields with unactivated, neutral, and activated aryl chlorides and bromides. In both reactions, extremely hindered substrates such as tri-ortho-substituted biaryls and tetra-ortho-substituted diarylamines can be produced without loss of activity. Finally, the present catalytic system has proven to be efficient with as low as 10 parts-per-million (ppm) of precatalyst in the Buchwald-Hartwig reaction and 50 ppm in the Suzuki-Miyaura reaction.     

Highly active Pd(II) catalysts with trans-bidentate pyridine ligands for the Heck reaction

[reaction: see text] The air-, water-, and heat-stable palladium(II) complexes 2a and 2b are prepared by the reaction of palladium(II) salts with the new trans-bidentate nitrogen ligands, 1,2-bis(2-pyridylethynyl)benzenes. The structure of complex 2a has been confirmed by X-ray structure analysis. The complexes efficiently catalyze the Heck olefination of aryl iodides and provide a good yield under phosphine-free conditions. The reaction is very sensitive to the nature of the chelating ligand.     

Non-symmetrically substituted di-N-heterocyclic carbene palladium(II) complexes: Synthesis,structure and catalytic activity

The synthesis and characterization of non-symmetric di-N-heterocyclic carbene (diNHC) silver(I) and palladium(II) complexes are described. The activity of the Pd(II) complexes in the Suzuki–Miyaura coupling reaction of bulky substrates was investigated. This synthetic route represents a possible general pathway into a wide variety of non-symmetrically substituted diNHC ligands.     

Intramolecular cyanoboration of alkynes via activation of boron-cyanide bonds by transition metal catalysts

Cyano(dialkylamino)boryl ethers of homopropargylic alcohols undergo intramolecular addition of a B-CN bond across their carbon-carbon triple bonds (cyanoboration) in the presence of palladium and nickel catalysts, furnishing five-membered cyclic boryl ethers regioselectively in good yields via 5-exo cyclization. The products were transformed into highly substituted α,β-unsaturated nitriles via Suzuki-Miyaura coupling to aryl iodides, rhodium-catalyzed conjugative addition to methyl vinyl ketone, and rhodium-catalyzed protodeborylation.     

Suzuki–Miyaura coupling reactions of aryl chlorides catalyzed by a new nickel(II) σ‐aryl complex

A new nickel(II) σ‐aryl complex, trans‐chloro(9‐phenanthrenyl)bis(triphenylphosphine)nickel(II), was used as a precatalyst for the Suzuki–Miyaura coupling reactions of aryl chlorides. The catalytic conditions were optimized by investigating the cross‐coupling of p‐chloroanisole with phenylboronic acid. The results show that this complex is efficient for both electron‐rich and electron‐deficient aryl chlorides, though it gives better yields for activated arylboronic acids than deactivated ones. All isolated cross‐coupled biaryl products have been characterized by ¹H and ¹³C NMR, and their spectral data are consistent with those reported. Side products from the coupling of arylboronic acid with the precatalyst complex have also been isolated and characterized, which is helpful for understanding the coupling mechanism. Copyright © 2013 John Wiley & Sons, Ltd.     

An inexpensive and highly stable ligand 1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)piperazine for Mizoroki-Heck and room temperature Suzuki-Miyaura cross-coupling reactions

A bulky, inexpensive and simple bidentate ligand 1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)piperazine (1) has been synthesized and characterized. The palladium catalyst was formed by combination of 1 with [Cl₂Pd(COD)] in a ratio of 1:1, tested in the Suzuki-Miyaura and Mizoroki-Heck cross-coupling reactions. Coupling of a variety of aryl bromides with phenylboronic acid using methanol as solvent at room temperature, or at 60 °C, gave generally high yields of coupled products. Coupling of aryl chlorides with organoboron reagent at 110 °C in DMF afforded good yields of biaryls under aerobic conditions. This non-phosphorus, air and moisture stable catalyst also displays good activity for Mizoroki-Heck coupling reaction in methanol at 60 °C with various aryl chlorides and bromides.     

Practical preparation method of polymer-incarcerated (PI) palladium catalysts using Pd(II) salts

[reaction: see text]. Polymer-incarcerated (PI) palladium catalyst was practically prepared from inexpensive Pd(II) salts and a polystyrene-based copolymer under reducing conditions. Remarkable effects of alkali metal salts on the palladium loading were observed. PI Pd thus prepared showed high catalytic activity in Mizoroki-Heck reactions and Suzuki-Miyaura couplings with a range of substrates including an aryl chloride. In all cases, the Pd catalyst was recovered quantitatively without leaching, and reused several times without significant loss of activity.     

有机-无机杂化材料负载的钯催化剂: 一种新型有效而可循环的无铜Sonogashira偶联反应

本文报道了有机-无机杂化材料固载的钯催化的无铜Sonogashira偶联反应。在3-[N,N-双（二苯基膦）氨基）]丙基功能化的硅胶固载的钯催化下,末端炔烃和碘代芳烃、溴代芳烃的偶联反应生成高产率相应的偶联产物。反应条件包括使用乙二醇为溶剂,三乙胺为碱。而且硅胶负载的膦钯催化剂和溶剂乙二醇经简单处理,可循环使用6次不降低活性。     

Highly efficient copper(0)-catalyzed Suzuki-Miyaura cross-coupling reactions in reusable PEG-400

Readily available copper powder with K₂CO₃ as the base was extremely effective catalyst for Suzuki-Miyaura coupling reaction performed in PEG-400, which afforded almost quantitative coupling products of aryl iodides. Using iodine as additive, coupling products of aryl bromides or chlorides could be obtained with moderate to good yields.     

Palladium‐Catalyzed Fluorosulfonylvinylation of Organic Iodides

A palladium‐catalyzed fluorosulfonylvinylation reaction of organic iodides is described. Catalytic Pd(OAc)₂ with a stoichiometric amount of silver(I) trifluoroacetate enables the coupling process between either an (hetero)aryl or alkenyl iodide with ethenesulfonyl fluoride (ESF). The method is demonstrated in the successful syntheses of eighty‐eight otherwise difficult to access compounds, in up to 99 % yields, including the unprecedented 2‐heteroarylethenesulfonyl fluorides and 1,3‐dienylsulfonyl fluorides.     

Monodentate phosphorus-coordinated palladium(Ⅱ)complexes as new catalyst for Mizoroki-Heck reaction of aryl halides with electron-deficient olefins

Four novel monodentate phosphorus-coordinated palladium(Ⅱ) complexes derived from 3,5-disubstituted-1H-1,2,4-diazaphospholes were developed as efficient catalyst for Mizoroki-Heck reactions of aryl halides with electron-deficient olefins. The role of these monophosphine ligands in catalysis was illustrated by control experiments using Pd salt and ligands as combined catalyst.     

New efficient approach to 2,2-diaryl-1,1-difluoro-1-alkenes and 1,1-difluoro-2-aryl-1,3-dienes via Suzuki coupling of alpha-halo-beta,beta-difluorostyrenes

[reaction: see text] Alpha-halo-beta,beta-difluorostyrenes [ArCX = CF2; X = Br, I; Ar = aryl, heteroaryl; synthesized by the Pd(0)-catalyzed coupling reaction of the corresponding alpha-halo-beta,beta-difluoroethenylzinc reagents (CF2=CXZnCl, X = Br, I) with aryl iodides] were functionalized at the halogen site with arylboronic acids under Pd(0)-catalyzed Suzuki-Miyaura coupling reaction conditions to obtain 2,2-diaryl-1,1-difluoro-1-alkenes (ArAr'C=CF2, Ar' = aryl, heteroaryl) in 51-91% isolated yield. The corresponding reaction with alkenylboronic acids produced 1,1-difluoro-2-aryl-1,3-dienes in 53-80% isolated yield. Alternatively, 2,2-disubstituted-1,1-difluoro-1-alkenes were synthesized in moderate yield by a zinc-insertion reaction at the halogen site of the alpha-halo-beta,beta-difluorostyrenes, followed by Pd(0)-catalyzed cross-coupling of the zinc reagent with aryl or alkenyl iodides.     

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.     

Organometallic chemistry of azuliporphyrins: synthesis, spectroscopy, electrochemistry, and structural characterization of nickel(II), palladium(II), and platinum(II) complexes of azuliporphyrins

Four azuliporphyrins, two meso-unsubstituted and two meso-tetraaryl substituted, were investigated in the synthesis of novel organometallic compounds. The meso-unsubstituted or "etio" series azuliporphyrins 8 reacted with nickel(II) acetate, palladium(II) acetate, and platinum(II) chloride in DMF to give the corresponding chelates 14-16, where the metal cation lies within the macrocyclic cavity and binds to all three nitrogens and the internal carbon atom. The newly available meso-tetraarylazuliporphyrins 13 similarly afforded the corresponding nickel(II), palladium(II), and platinum(II) complexes, 17-19, respectively. The new organometallic complexes are stable nonpolar compounds and were fully characterized spectroscopically and by mass spectrometry. The UV-vis data indicate that these complexes, in common with the parent azuliporphyrin system 8, do not possess porphyrin-type aromaticity. However, electron donation from the azulene unit can give rise to dipolar resonance contributors that provide a degree of carbaporphyrin-type aromatic character. The platinum(II) azuliporphyrins 16 gave noteworthy proton NMR spectra where the meso-protons showed satellite peaks due to transannular coupling to platinum-195. The pyrrolic protons of the platinum(II) meso-tetraarylazuliporphyrin 19b also showed similar satellite peaks due to coupling from the platinum-195 isotope. The electrochemistry of free base tetraphenylazuliporphyrin 13a and the related nickel(II) and palladium(II) complexes was investigated using cyclic voltammetry, and these data indicate that metal coordination improves the reversibility of the ligand-based oxidations. Nickel(II) azuliporphyrin 14a and palladium(II) tetrakis(4-chlorophenyl)azuliporphyrin 18b were also structurally characterized by X-ray crystallography. The macrocyclic core of the palladium(II) complex 18b was significantly more planar than the nickel(II) derivative 14b, and this difference was attributed to the better size match between the azuliporphyrin cavity and the larger palladium(II) ion. The straightforward synthesis of metalloazuliporphyrins under mild conditions, and their interesting spectroscopic, electrochemical, and structural features, demonstrates that the azuliporphyrin system holds great promise as a platform for organometallic chemistry.     

Tributyltin Aryl Selenides as Efficient Arylselenating Agents. Synthesis of Diaryl and Aryl Organyl Selenides

Tributyltin aryl selenides are highly efficient arylselenating agents in reactions with aryl iodides and aryl triflates under catalysis with Pd and Ni complexes respectively. They also may be used as efficient source of active arylselenolate anion in the presence of fluoride ions in reaction of arylselenation of alkyl halides and activated aryl fluorides.