Pd-catalyzed Suzuki Reaction Research Articles

Ultrafast Dynamics and Strong Two-Photon Absorption Properties of Nonplanar β-Functionalized “Push–Pull” Copper Corroles with a Mixed Substituent Pattern

A new series of nonplanar and unsymmetrically β-functionalized "push-pull" copper corroles, CuTPC(CHO)R7 [R = H, Br, Ph, Me, or 2-thienyl (Th)], were synthesized and characterized to elucidate the effect of β-functionalization and nonplanarity on the photophysical, redox, and nonlinear optical (NLO) properties on the corrole ring. The synthetic route to unsymmetrically β-octasubstituted copper corroles includes bromination of CuTPC(CHO) to get CuTPC(CHO)Br7 in 80% yield, which was further subjected to the Pd-catalyzed Suzuki reaction. CuTPC(CHO)Br7 exhibited a large red shift in the Soret band (Δλmax = 35-40 nm) and both the Q bands (Δλmax = 10-50 nm), as compared to CuTPC and CuTPC(CHO). CuTPC(CHO)Br7 was 510 and 290 mV anodically shifted in the first oxidation and the first reduction compared to CuTPC owing to the strong -I effect of CHO and Br groups. Density functional theory studies revealed that all the β-octasubstituted copper corroles exhibited highly nonplanar saddle-shape conformation of the corrole ring. Very high torsional saddling was observed for CuTPC(CHO)Th7 (79-83°) than that for CuTPC (49-53°), even larger than that for CuTPCBr8 (67-70°). Femtosecond laser-induced third-order NLO studies from these copper corroles showed strong two-photon absorption cross-sections (0.48-6.98 × 104 GM) and self-focusing-type positive nonlinear refraction behavior. The observed structure-dependent two-photon absorption coefficients (β) are in the range of ∼2.7-20.9 × 10-12 m/W, and the n2 values are in the range of ∼0.64-6.45 × 10-18 m2/W. The present results may facilitate a new window for these copper corroles in nonlinear optical devices, femtosecond optical limiters, and many other ultrafast photonic applications.

Synthesis of glucopyranoside benzimidazolium-based ionic liquids for Pd-catalyzed aqueous Suzuki reaction

Several novel benzimidazolium-based ionic liquids (BzIm ILs) with free and acetyl protected glucopyranoside unit were synthesized and used as ligand for Pd-catalyzed environment-friendly Suzuki reaction. The BzIm ILs with the acetyl protection shows the highest activity, probably because the sugar has a large steric hindrance and acetyl groups can coordinate with Pd. The nuclear magnetic resonance spectra of Pd(OAc)2/Glc-BzIm ILs free glucopyranoside indicate that Pd-C is formed. The Pd nanoparticles protected by ILs with a size of 5.3 (0.6) nm are considered to be real active species. A series of fluorene core arylfluorene derivatives were prepared with isolated yields above 90%.

The Stereochemical Course of Pd-Catalyzed Suzuki Reactions Using Primary Alkyltrifluoroborate Nucleophiles.

Using deuterium-labeled stereochemical probes, we show that primary alkyltrifluoroborate nucleophiles undergo transmetalation to palladium exclusively via a stereoretentive pathway and that the resulting stereospecificity is broadly independent of electronic and steric effects. This stands in stark contrast to the stereochemical course of transmetalation for secondary alkyltrifluoroborates, which varies between net stereoretention and net stereoinversion depending upon the electronic properties of the supporting phosphine ligand, the electronic properties of the aryl electrophile, and the steric properties of the alkylboron nucleophile. In this study, we additionally show that the stereochemical course of transmetalation for secondary alkylboron reagents can be under reagent steric control, while no such steric control exists for analogous primary alkylboron nucleophiles. The combined study reveals fundamental mechanistic differences between transmetalations of primary and secondary alkylboron reagents in Pd-catalyzed Suzuki reactions.

N,S-chelating triazole-thioether ligand for highly efficient palladium-catalyzed Suzuki reaction

1,2,3-Triazole-thioether compounds could serve as efficient ligands for Pd-catalyzed Suzuki reactions of various aryl iodides, bromides and chlorides. The reactions feature wide substrate scope and mild reaction conditions. Besides, shorter reaction time, lower catalyst loadings and quantitative yields with a turnover-frequency (TOF) value of up to 11,880 h−1 are other advantageous of this attractive protocol. The crystal structure analyses and computational studies revealed that the higher catalytic activity of the corresponding chelated palladium complex ascribed to the lower energy gap and the lower redox potential.

Synthesis of Nucleobase-Functionalized Morpholino Monomers.

Morpholino antisense oligonucleotides are used as routine tools in developmental biology to investigate gene function during early embryogenesis. These chemically modified oligos contain morpholine ring connected with phosphorodiamidate linkages as backbone but carry unmodified nucleobases. In this chapter, we describe the methods to further modify the nucleobases using palladium-catalyzed cross-coupling reactions. The key reactions used are halogenations of the nucleobases in suitable position and subsequent Pd-catalyzed Sonogashira and Suzuki reactions. The sequential synthetic steps are described in detail in this chapter, and the examples are shown in tables.

Green, Efficient and Reusable Bis(imidazolium) Ionic Liquids Promoted Pd-Catalyzed Aqueous Suzuki Reaction for Organic Functional Materials

Glucopyranoside-substituted asymmetric bis(imidazolium) ionic liquids were used to promote environmentally friendly, efficient and reusable Pd-catalyzed Suzuki reaction between arylboronic acids and 2-bromofluorene, 2,7-dibromo-9,9′-dialkylfluorene. Over 30 carbazole-based fluorene core potential organic functional materials were synthesized. In addition, recyclability of catalyst system was inspected on the Suzuki reaction observing nearly no loss in catalytic activity up to five cycles. Development of green, efficient and recycle glucopyranoside substituted bis(imidazolium) ILs promoted Pd-catalyzed aqueous Suzuki reaction for OFMs.

Deep red aggregation-induced CPL emission behavior of four-component tunable AIE-active chiral polymers via two FRET pairs mechanism

Two four-component chiral polymers with two Förster resonance energy transfer (FRET) pairs incorporating chiral 1,1′-binaphthyl, 4,7- di(thiophen-2-yl)-2,1,3-benzothiadiazole (DTBT), tetraphenylethene (TPE) and fluorene moieties were designed and synthesized via one-pot two-step of Pd-catalyzed Sonogashira reaction and Suzuki reaction by changing different ratios of DTBT chromophore and AIE-active TPE group. Both chiral polymers exhibit large Stokes shift (257 nm) and tunable red aggregation-induced emission (AIE) response behavior via two intramolecular FRET pairs by changing excitation wavelength. Interestingly, the chiral polymer with lower ratio of DTBT (P-1) shows obvious aggregation-induced circularly polarized luminescence (AICPL) emission signals in deep red region (around 650 nm) and higher glum, which can reach as high as ±2.0 × 10-3 in THF-H2O mixtures.

Electrochemiluminescent resonance energy transfer of polymer dots for aptasensing

This work designed a three-component polymer for the preparation of polymer dots (Pdots). The polymer contained 9-(diphenylmethylene)-9H-fluorene (DPF), 9,9-dioctyl-9H-fluorene (DOF) and 1,1′-binaphthyl moieties, and was synthesized via Pd-catalyzed Suzuki reaction. It exhibited obvious yellow-colored aggregation-induced emission (AIE) for fluorescence enhancement at 543nm via an intramolecular fluorescence resonance energy transfer from DOF moiety to DPF moiety. The Pdots prepared by nanoprecipitation could be conveniently cast on electrode surface and showed a stable anodic electrochemiluminescence (ECL) emission in the presence of triethylamine as a co-reactant. The ECL emission could be effectively quenched by rhodamine B via resonance energy transfer, which led to an “off-on” switch for the design of ECL sensing methodology. Using Pb2+ as a target model, an ECL aptasensor for the detection of trace Pb2+ was proposed, which showed a linear range of 100pM to 1.0μM with a detection limit down to 38.0pM This work demonstrated the first Pdots prepared with AIE-active polymer for highly efficient ECL sensing.

Sigma-spacer regulated thiophenyl triazine conjugates: synthesis and crystal, electronic and luminescent properties

Water-accelerated Pd-catalyzed Suzuki reaction for synthesis of TTCs. Sigma-spacer and position isomerism finely tuned the luminescent properties.

Synthesis of Chiral Imidazolium Salts from a Carbohydrate and Their Application in Pd-Catalyzed Suzuki–Miyaura Reaction

A series of chiral 1-(acetylated glucopyranosyl)-3-substituted-imidazolium salts [3-substitute = n-butyl (1a), 3-bromopropyl (1b), 2-chloromethyl benzyl (1c), and 4-chloromethyl benzyl (1d)] have been synthesized. Preliminary catalytic studies show that these imidazolinium salts are remarkably efficient in Pd-catalyzed Suzuki–Miyaura reaction. Functionalized aryl boronic acids reaction with aryl halides (including aryl iodides, aryl bromides and activated aryl chlorides) using environmentally friendly conditions (ethanol aqueous and ambient). The excellent isolate yields reveal that the bulky carbohydrate unit is promising for the construction of highly active transition-metal catalyst. Four C-1 bonded sugar-containing chiral imidazolium salts 1a–d were synthesized and they all exhibited excellent catalytic activity in Pd-catalyzed Suzuki reactions. Pd/1a is most effective for the coupling of functionalized arylboronic acids with arylhalides including activated arylchlorides in ethanol aqueous under air.

Synthesis of benzimidazo[2,1-b]benzothiazole derivatives through sequential Cu-catalyzed domino coupling and Pd-catalyzed Suzuki reaction

A variety of benzo[d]benzo[4,5]imidazo[2,1-b]thiazoles were efficiently and conveniently synthesized from the Cu-catalyzed domino coupling of o-dihaloarenes with 2-mercaptobenzimidazoles. The reaction is also applicable to a series of multi-functional substrates, affording the halo-containing products with excellent selectivity. The brominated products can further react with arylboronic acids under Pd catalysis to furnish the aryl-substituted benzimidazo[2,1-b]benzothiazole derivatives.

Pd-catalyzed ligand-free Suzuki reaction of β-substituted allylic halides with arylboronic acids in water

The combination of Pd(TFA)2 and KOH could efficiently catalyze the reaction of β-substituted allylic halides with arylboronic acids in water.

PEG-functionalized NHC ligands for efficient and recyclable palladium-catalyzed Suzuki reactions in water

We have used poly(ethylene glycol)-functionalized N-heterocyclic carbene ligands, 1-(methoxy PEG)-3-methylimidazolium iodides together with Pd(OAc)2 as efficient catalysts for the Suzuki reaction in water. The best catalytic system generated in situ from Pd(OAc)2, mPEG16MeImI, and K2CO3 is able to mediate the Suzuki coupling of a series of aryl boronic acids and aryl halides, except for deactivated aryl chlorides, in good to almost quantitative yields in water within 6 h. After extraction of the product, the catalyst containing mPEG n MeImI phase could be recycled for five times without significant loss of activity. Three PEG-modified NHC ligands with different PEG chain lengths (mPEGnMeImI, n = 7, 12, and 16) were used for Pd-catalyzed Suzuki reactions in water. The best catalytic system generated in situ from Pd(OAc)2, mPEG16MeImI, and K2CO3 is able to mediate the Suzuki coupling of a series of aryl boronic acids and aryl halides, except for deactivated aryl chlorides, in good to almost quantitative yields in water within 6 h. After extraction of the product, the catalyst containing mPEG n MeImI phase could be recycled for five times without significant loss of activity.

A highly active and stable imidazolidine-bridged N,O-donor ligand for efficient palladium catalyzed Suzuki–Miyaura reactions in water

We have used the sterically hindered N,O-donor ligand 1,4-bis(2-hydroxy-3,5-di-tert-butyl-benzyl)-imidazolidine with various Pd salts as a catalyst for the Suzuki reaction. This system exhibited excellent catalytic activity in Suzuki reactions of arylboronic acids with aryl halides, including aryl iodides, aryl bromides and activated aryl chlorides, using aqueous methanol as solvent under mild conditions. The catalytic system can be reused once without significant loss of activity. The sterically hindered imidazolidine-bridged mixed nitrogen, oxygen ligand 1 was efficient for Pd-catalyzed Suzuki reactions involving aryl iodides, aryl bromides and activated aryl chlorides with arylboronic acid in aqueous methanol with K2CO3 as a base the high catalytic activity and oxygen or moisture stable of palladium complexes maybe distribute to the bulky tert-butyl effect.

Novel syntheses and properties of meso-tetraaryl-octabromo-tetranaphtho[2,3]porphyrins (Ar4Br8TNPs)

o-Quinodimethane (o-QDM) generated from benzosultine was used to extend the pyrrole system for the preparation of octabromo-tetranaphtho[2,3]porphyrins via oxidative aromatization. The properties of these bromoporphyrins were presented and chemical transformation via Pd-catalyzed Suzuki reaction was also effectively achieved.

4‐Aryl‐Substituted 2,5‐Dimethoxyphenethylamines: Synthesis and Serotonin 5‐HT2A Receptor Affinities

A series of novel ligands for the serotonin 5-HT(2A/C) receptor subtype bearing the 2-phenylethylamine pharmacophore was synthesized and assayed for its 5-HT(2A) receptor binding affinity. As the 4'-aryl-substituted 2-(2,5-dimethoxyphenyl)ethylamines were previously unknown, an initial series of twelve compounds was chosen to obtain initial insight into their structure-activity relationships. The 4'-aryl moiety was introduced in moderate-to-high yield by a Pd-catalyzed Suzuki reaction of twelve arylboronic acids with N-Boc-protected 2-(2,5-dimethoxy-4-iodophenyl)ethylamine (8). N-Boc Deprotection then afforded the novel 2-phenylethylamines 5a-5l. Additionally, biphenyl compound 6 lacking the 5'-MeO substituent was prepared, starting from 2-methoxy-4-hydroxybenzaldehyde. Except for 5l, all of the compounds proved to be antagonists with generally low affinity at the rat 5-HT(2A) receptor. Substituents are generally not well tolerated on the 4'-aryl moiety, except in the 4''-position. Indeed, the relatively high affinity of the 4''-butyl-, 4''-phenyl-, and 4'-naphthyl-substituted compounds 5i, 5k, and 5e, respectively (K(i)=32, 33, and 41nM, resp.), attests a rather remarkable tolerance for bulk in this location.

Chemoselective three-component coupling via a tandem Pd-catalyzed boron-Heck and Suzuki reactions

A new approach is herein reported to prepare biaryl derivatives via a tandem Pd-catalyzed boron-Heck and Suzuki reactions. This one-pot tandem process avoided purification or addition of extra catalyst between steps. The resulting biaryl compounds can be prepared with substrate variability in good to moderate yields.

Asymmetric addition of phenylacetylene to aldehydes catalyzed by soluble optically active polybinaphthols ligand

A chiral polymer ligand was synthesized by the polymerization of ( S)-5,5′-dibromo-6,6′-dibutyl-2,2′-binaphthol ( S-M-1 ) with ( S)-2,2′-bishexyloxy-1,1′-binaphthyl-6,6′-boronic acid ( S-M-2 ) via Pd-catalyzed Suzuki reaction. The application of the chiral polymer ligand to the asymmetric addition of phenylethynyl zinc to various aldehydes has been studied. The results show that the soluble chiral polybinaphthols ligand in combination with Et 2Zn and Ti(O i Pr) 4 can exhibit excellent enantioselectivity for phenylacetylene addition to both aromatic and aliphatic aldehydes. The catalytically active center of the repeating unit S-1 used as a catalyst produced the opposite configuration of the propargylic alcohols to that of S-1 , on the contrary, the chiral polymer gave the same configuration as the optically active binaphthol moiety of the polybinaphthols ligand. Moreover, the chiral polymer ligand can be easily recovered and reused without loss of catalytic activity as well as enantioselectivity.

1,3-Dicarbonyl compounds as phosphine-free ligands for Pd-catalyzed Heck and Suzuki reactions

Some 1,3-dicarbonyl compounds (such as pentane-2,4-dione and 3-oxo- N-phenylbutanamide) were found to constitute highly efficient, yet low-priced and phosphine-free ligands for the Pd-catalyzed Heck and Suzuki reactions of aryl bromides and iodides with very high turnover numbers (ca. 10 3–10 4).

Low melting sugar–urea–salt mixtures as solvents for organic reactions—estimation of polarity and use in catalysis

Mixtures of sugars, sugar alcohols or citric acid with urea and inorganic salts form stable melts if heated to 70 °C. The polarity of the melts was estimated using solvatochromic dyes and found to be in the range of DMF or water, depending on the sensitivity of the dye for hydrogen bonds. To explore the use of the melts as solvents in catalysis, Rh-catalyzed hydrogenations and Pd-catalyzed Suzuki reactions were performed. The hydrogenation of a double bond is sensitive to the composition of the melt, and no effect of the chiral melts on the stereochemical outcome of the reaction was observed. The Suzuki coupling proceeds rapidly, cleanly and quantitatively in all examined melts. The results recommend the non-toxic sugar–urea–salt melts as more sustainable reaction media for chemical transformations.