Sonogashira-Hagihara Coupling Research Articles

Microwave‐Promoted Copper‐Free Sonogashira–Hagihara Couplings of Aryl Imidazolylsulfonates in Water

AbstractAryl imidazol‐1‐ylsulfonates have been efficiently cross‐coupled with aryl‐, alkyl‐, and silylacetylenes in neat water under copper‐free conditions at 110 °C assisted by microwave irradiation. Using 0.5 mol% of an oxime palladacycle as precatalyst, 2‐dicyclohexylphosphino‐2′,6′‐dimethoxybiphenyl (SPhos, 2 mol%) as ligand, hexadecyltrimethylammonium bromide (CTAB) as additive, and triethylamine (TEA) as base, a wide array of disubstituted alkynes has been prepared in good to high yields in only 30 min.

Synthesis and tuning of optical properties of conjugated polymers involving benzo[h]quinoline-based neutral pentacoordinate organosilicon complexes in the main chain

We present the synthesis and optical properties of a series of alternating polymers containing pentacoordinate silicon complexes in the main chain. By employing the benzo[h]quinoline ligand, the pentacoordinate silicon complexes were obtained. The polymers were prepared via the Sonogashira–Hagihara coupling reaction. From the series of measurements for optical properties of the synthesized polymers, new absorption bands and bathochromic shifts in emission spectra were observed. These data suggest that intramolecular charge transfer could occur after the excitation because of the elongation of π-conjugation via the polymer main chains. The modulation of the optical properties of the conjugated polymers involving the pentacoordinate silicon was accomplished.

ChemInform Abstract: Copper‐ and Amine‐Free Sonogashira—Hagihara Coupling Reaction Catalyzed by Pd(0) Nanoparticles Supported on Modified Crosslinked Polyacrylamide.

AbstractThe method requires tetrabutylammonium bromide which acts as base and phase‐transfer catalyst.

Stabilization of higher-order structure of poly(phenyleneethynylene)s by metathesis polymerization at the side chains

Novel poly(m-phenyleneethynlene-p-phenyleneethynylene)s bearing polymerizable diene or norbornene groups were synthesized by the Sonogashira–Hagihara coupling polymerization of the corresponding d-hydroxyphenylglycine-derived diiodo monomers with p-diethynylbenzene. These polymers exhibited strong Cotton effects derived from a predominantly one-handed helical conformation in CHCl3 and tetrahydrofuran, but exhibited weak or no Cotton effects in N,N-dimethylformamide. The metathesis polymerization of the diene and norbornene moieties was performed at the side chains of the polymers under diluted conditions in the presence of a chain-transfer agent, if necessary. The reaction took place intramolecularly, which was confirmed by size exclusion chromatography (SEC) measurements. The polymers exhibited stronger Cotton effects even in polar media after the intramolecular crosslinking, which indicated stabilization of the predominantly one-handed helical structures.

Synthesis and Characterization of [2.2]Paracyclophane-Containing Conjugated Microporous Polymers

Conjugated microporous polymers (CMPs) are prepared from disubstituted and tetrasubstituted [2.2]paracyclophane monomers by a Sonogashira–Hagihara coupling. The polymers obtained exhibit a type I nitrogen gas adsorption profile and H4-like hysteresis loops, indicating that the [2.2]paracyclophane-containing CMPs possess slit-like mesopores. Their Brunauer–Emmett–Teller surface areas are estimated to be above 500 m2 g−1. The step and stacked structure of the [2.2]paracyclophane unit affects the morphology of the polymers because of the contribution of two-dimensional expansion of the polymer network.

Palladium nano-particles supported on agarose as efficient catalyst and bioorganic ligand for C[sbnd]C bond formation via solventless Mizoroki–Heck reaction and Sonogashira–Hagihara reaction in polyethylene glycol (PEG 400)

In this study, abundant naturally occurring agarose has been used as a support and ligand for palladium nanoparticles. In the presence of this catalytic system, Mizoroki–Heck and Sonogashira–Hagihara coupling reactions were performed successfully. The catalyst exhibits high activity in Mizoroki–Heck reaction under phosphane and solvent-free conditions for the reaction of iodo- and bromoarenes with butyl acrylate and styrene. This catalytic system also showed high catalytic activity for Sonogashira–Hagihara coupling reaction of various aryl halides (I, Br, Cl) under copper and ligand-free conditions in polyethylene glycol (PEG 400) as an ecofriendly and non-poisonous media. The catalyst can be separated from the reaction mixture and reused for the similar batches of the reaction. High efficiency of the catalyst along with its recycling ability and the rather low Pd-loading which are demonstrated in both Mizoroki–Heck and Sonogashira–Hagihara reactions are the merits of the presented catalyst system.

Sonogashira–Hagihara Coupling towards Diaryl Alkynes Catalyzed by FeCl3⋅6 H2O/Cationic 2,2'‐Bipyridyl

AbstractEfficient and environmentally benign one‐pot Sonogashira–Hagihara coupling of aryl iodides with 4‐aryl‐2‐methylbut‐3‐yn‐2‐ols catalyzed by an FeCl3⋅6 H2O/cationic 2,2'‐bipyridyl system in water under air in the presence of zinc powder reductant was performed. Various aryl iodides and 4‐aryl‐2‐methylbut‐3‐yn‐2‐ols were used as reactants, which afforded moderate to high yields of cross‐coupled products. Although alkyl‐substituted 2‐methylbut‐3‐yn‐2‐ol could not be coupled with aryl iodides, the use of alkyl terminal alkynes under similar conditions provided the corresponding products in moderate yields. This reaction protocol was also used to synthesize both symmetric and asymmetric 1,4‐diarylbuta‐1,3‐diynes. This one‐pot iron‐catalyzed Sonogashira–Hagihara coupling reaction progressed without the use of an organic solvent, a copper cocatalyst, or an inert atmosphere, rendering it an environmentally friendly method with potential for practical applications.

Synthesis of π‐Conjugated Polymers Containing Aminoquinoline‐Borafluorene Complexes in the Main‐Chain

The regulation of electron transfer between a conjugated polymer and ligands orthogonally connected to the main-chain is reported. Poly(arylene-ethynylene)s containing aminoquinoline-borafluorene complexes in the main-chain are synthesized in good yields by a Sonogashira-Hagihara coupling. Single crystal X-ray analysis of a model compound has elucidated the complex's structure in which the aminoquinolate moiety and the borafluorene ring are connected directly and orthogonally. Moreover, the optical properties of the polymers are characterized by UV-vis absorption and photoluminescence spectra. Perfluorinated alkyl chain-containing polymers show strong emission, while hydrocarbon chain-containing ones exhibit only a slight emission. DFT calculation suggests that an electron transfer from the excited main-chain to the aminoquinolate ligand is suppressed because of the lowered LUMO level by introducing the electron withdrawing groups, resulting in the significant emission.

Synthesis of benzo[h]quinoline-based neutral pentacoordinate organosilicon complexes

Reactions of 10-benzo[h]quinolyllithium with a series of organosilanes led to the formation of neutral pentacoordinate complexes. The diethynyl-substituted complex was able to be converted to di(arylethynyl)-substituted ones by the Sonogashira-Hagihara coupling reaction. Electronegative substituents shortened N-Si distances and enhanced fluorescence intensity from the complexes.

Synthesis and characterization of optically active poly(phenylene-ethynylene)s containing chiral oxazoline derivatives

Novel optically active (S)-2-(3,5-diiodophenyl)oxazoline derivatives ((S)-DIPhROx)) (R=4-benzyl (1a), 4-phenyl (1b)) were synthesized and polymerized using the Sonogashira–Hagihara coupling reaction to obtain the poly(phenylene-ethynylene)s bearing oxazoline derivatives in the weight range from 1060 to 17 300 in 40–72% yields. The polymers were thermally stable up to 220 °C. All the polymers exhibited higher specific rotation values than the model compound did. Moreover, these polymers also showed intense circular dichroism (CD) signals in the transition region of the conjugated main chain, whereas almost no induced Cotton effect was observed for the model compound. The results of the specific rotation and CD and ultraviolet analyses indicate that the optical activities of the polymers arise not only from the configurational chirality of the optically active oxazoline pendant groups but also from elements of higher-order structure such as the helical conformation. Optically active 4-alkyl-2-(3,5-diiodophenyl)oxazoline was synthesized and polymerized by the Sonogashira–Hagihara coupling reaction to obtain the poly(phenylene-ethylnylene)s bearing oxazoline derivatives with number-average molecular weight ranging from 1060 to 17 300 in 40–72% yields. All the polymers exhibited higher values of specific rotation ([α]D=+41.6 to +83.7°) than the monomer ([α]D=−1.2 to −16.9°). On the basis of the results of specific rotation, circular dichroism and ultraviolet analyses, the optical activities of the polymers arise from not only the configurational chirality of the optically active oxazoline pendant groups but also the higher-order structure such as helical conformation.

Metallopolymers Featuring Boratabenzene Iron Complexes

Boratabenzene-derived metallocene analogues are introduced as versatile new building blocks for metallopolymers. Bis(borinato)iron(II) complexes of the type Fe(C(5)H(5)B-R)(2) (R: C≡CH, C≡CSiMe(3), 4-(1-benzyl-1,2,3-triazolyl) were synthesized and spectroscopically, structurally, and electrochemically characterized. Polymerization via Sonogashira-Hagihara coupling of the alkynyl-substituted derivative Fe(C(5)H(5)B-C≡CH)(2) with 2,5-bis(dodecyloxy)-1,4-diiodobenzene yields a film-forming polymer in 50-69% yield. Polymer batches were obtained with number-average molecular weights (M(n)) of 11.7 and 20.5 kDa and polydispersity indices (PDI) of 1.55 and 2.65, respectively, as determined by gel permeation chromatography relative to polystyrene standards. Click-type polymerization of Fe(C(5)H(5)B-C≡CH)(2) through azide-alkyne cycloaddition with 1,4-bis(4-azidobutoxy)benzene gives the corresponding metallopolymer with an M(n) of 5.7 kDa and a PDI of 2.29 in 87% yield.

Aromatic-ring-layered polymers composed of fluorene and xanthene

Aromatic-ring-layered polymers were synthesized by Sonogashira–Hagihara coupling reaction using xanthene as a scaffold. The polymers were characterized by various spectroscopic and electrochemical methods. The polymers emit brightly without excimer formation, despite the layered structure.

Synthesis and [2+2] Cycloaddition with Tetracyanoethylene of Ene–Diyne Scaffolds Bearing Ferrocenes at the Periphery

AbstractThe ene–diyne systems 1 and 2, possessing ferrocenyl groups at the periphery, were prepared by a simple one‐pot Sonogashira–Hagihara coupling reaction of ethynylferrocene with 9‐dibromomethylene‐9H‐fluorene (4) and 9,10‐bis(dibromomethylene)‐9,10‐dihydroanthracene (5). Ene–diyne 1 reacted with tetracyanoethylene (TCNE) in a formal [2+2] cycloaddition reaction, followed by ring opening of the initially formed [2+2] cycloadduct, cyclobutene, to afford the corresponding 1,1,4,4‐tetracyanobutadiene (TCBD) derivative 6 in good yield. The redox behavior of the ene–diyne compounds 1 and 2, and the TCBD derivative 6 was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their electrochemical oxidation properties with multi‐electron transfer depending on the number of ferrocene units in the molecule, in addition to the two‐electron reduction of the TCBD moiety in the case of TCBD derivative 6. Moreover, a significant color change was observed by visible spectroscopy under electrochemical oxidation conditions and under reduction conditions in the case of TCBD derivative 6.

Creation of Pd-nanoparticles within the pores of ring opening metathesis polymerization-derived polymeric monoliths for use in organometallic catalysis

Polymeric monolithic supports displaying micro-, meso- and macroporosity have been prepared via ring opening metathesis polymerization (ROMP) from (Z)-9-oxabicyclo[6.1.0]non-4-ene (OBN) and tris(cyclooct-4-en-1-yloxy)methylsilane (CL) by the use of the 2 nd -generation Grubbs-initiator RuCl2(Py)2(IMesH2)(CHPh) 1 in the presence of a phase separation-enforcing macroporogen, i.e. 2propanol, and a microporogen, i.e. toluene. The porous supports were then subject to pore sizeselective functionalization by hydrolyzing the epoxy-groups within pores >6 nm to the corresponding vic-diol with the aid of poly(styrenesulfonic acid) (PS-SO3H). The remaining epoxide moieties located within the small pores (diameter <6 nm) were then reacted with N,Ndipyrid-2-ylamine to yield the corresponding dipyrid-2-ylamin-functionalized monolithic supports. Typical loadings with functional monomer were in the range of 6-7 µmol/g. These chelating ligands located within the small pores were then used for the immobilization of Pd II . Quantitative metal loadings (approx. 1 mg/g) could be accomplished. Reduction of the Pd II with NaBH4 resulted in the formation of Pd nanoparticles <4 nm in diameter that were still exclusively located within the small pores. These Pd-loaded monoliths were used in a series of Sonogashira-Hagihara and Suzuki-type couplings. Scanning electron microscopy measurements on the metal loaded monoliths prior to the catalytic reactions revealed that the metal nanoparticles that formed were immobilized within the small pores. These findings are supported by the comparably low metal content in the coupling products. Thus, metal leaching was <0.13 %.

Copper- and amine-free Sonogashira–Hagihara coupling reaction catalyzed by Pd(0) nanoparticles supported on modified crosslinked polyacrylamide

Pd(0) nanoparticles supported on modified crosslinked polyacrylamide containing phosphinite ligand was prepared. The complex was a highly efficient catalyst for the Sonogashira– Hagihara coupling reaction in the absence of a copper cocatalyst and an amine base under aerobic condition. This protocol can be applied for different aryl halides including chloroarenes. The catalyst can be reused several times without any considerable decrease in its activity because of low leaching of palladium metal from the support. Transmission electron microscopy (TEM) analysis of the catalyst revealed the formation of stable and polydispersed Pd(0) nanoparticles.

A luminescent coordination polymer based on bisterpyridyl ligand containing o-carborane: two tunable emission modes

We designed a novel ditopic bisterpyridyl ligand containing o-carborane that can construct a coordination polymer by complexation with metal ions. Through the use of Sonogashira-Hagihara coupling, the desired ligand molecule was successfully synthesized. Addition of Zn(II) ions rapidly underwent the generation of a fluorescent coordination polymer, which was confirmed by (1)H NMR, UV-vis, and fluorescent titration experiments. Furthermore, the electronic structure of the bisterpyridyl ligand molecules was drastically changed upon the complexation with metal ions. The obtained coordination polymer showed light blue emission derived from the intraligand charge transfer (ILCT) state, whereas a bare ligand molecule exhibited yellowish-green aggregation-induced emission (AIE) in a poor solvent such as water, because of the variable C-C bond in o-carborane.

Gelatin as a bioorganic reductant, ligand and support for palladium nanoparticles. Application as a catalyst for ligand- and amine-free Sonogashira–Hagihara reaction

Palladium nanoparticles were deposited and reduced by gelatin as a safe edible, naturally occurring and cheap support. No extra reducing agents were used for the generation of Pd(0) nanoparticles from the Pd(II) salt. The nanoparticles of Pd supported on gelatin were characterized by SEM, TEM and AFM images, UV-Vis and XRD spectra and the amount of palladium entrapped in the gelatin was measured by ICP and atomic absorption analysis. The nanoparticles showed high catalytic activity for the Sonogashira-Hagihara coupling reaction of various aryl iodides, bromides and chlorides as well as heteroaryl halides and also β-bromo styrene with phenylacetylene under copper-, ligand- and amine-free conditions. The reactions were carried out at 100 °C in molten tetrabutylammonium bromide (TBAB) or polyethylene glycol (PEG400) in the presence of potassium acetate as a base in argon atmosphere. Dimerization of phenylacetylene applying similar conditions in air is also described.

Synthesis and Optical Properties of Molecular Rods Comprising a Central Core‐Substituted Naphthalenediimide Chromophore for Carbon Nanotube Junctions

AbstractThe synthesis of a series of molecular rods 1–5, designed to bridge the gap of a carbon nanotube junction in order to emit light as a characteristic signal of integrated molecules, is reported. The molecular rods consist of a central naphthalenediimide (NDI) core, which itself is substituted with benzylamino and benzylsulfanyl groups, providing distinct absorption and emission properties. The NDI core is embedded in an oligo(phenylene ethynylene) (OPE) system providing the rod‐like structure required to bridge gaps between nanoelectrodes. The number of repeating units of the OPE is varied to adjust the length of the target compounds between 2.3 and 6.6 nm. The OPE parts are terminally functionalized with polyaromatic hydrocarbon groups (naphthalene, phenanthrene, anthracene or pyrene), which possess affinity with the surface of the carbon nanotubes due to van der Waals interactions. Synthetic protocols based on Sonogashira–Hagihara couplings were developed to build up the OPE backbone. Bifunctional iodophenyl acetylene derivative 33 served as a key building block in a coupling–deprotecting–coupling sequence. The NDI building block was synthesized by an aromatic nucleophilic substitution reaction of 2,6‐dichloro‐1,4,5,8‐tetracarboxylic acid naphthalenediimide derivative 9 and the corresponding amine and sulfide (i.e., 11, 12), respectively. The convergent synthesis allows modular assembly of the NDI and OPE parts in a final Sonogashira–Hagihara coupling reaction. The target structures were fully characterized by NMR spectroscopy and mass spectrometry. Further, the optical properties of compounds 3–5 in solution, and on a graphene surface were qualitatively investigated. A Dexter‐type energy transfer from the OPE unit to the NDI unit was observed. The studies of target structures 3–5 revealed that diamino‐functionalized compound 3 is ideally suited for the envisaged single molecule electroluminescence experiments.

Synthesis of highly luminescent organoboron polymers connected by bifunctional 8‐aminoquinolate linkers

AbstractNew organoboron aminoquinolate‐based polymers linked by π‐conjugated bridge were prepared by Sonogashira–Hagihara coupling of organoboron aminoquinolate‐based bisiodo monomers bearing biphenyl or bithiophene moiety with 1,4‐diethynylbenzene derivatives. Tetracoordination states of boron atoms in the obtained polymers were confirmed by 11B NMR spectroscopy, and they were also characterized by 1H NMR and IR spectroscopies and size‐exclusion chromatography. Their optical properties were studied by UV–vis absorption and photoluminescence spectroscopies. In the region above 400 nm, the polymers prepared from 1,4‐diethynyl‐2,5‐dioctyloxybenzene showed bathochromic shifts when compared with those prepared from 1.4‐diethynyl‐2‐perfluorooctyl‐5‐trifluoromethylbenzene. The polymers with biphenyl moiety showed higher absolute fluorescence quantum yields (ϕF = 0.28 and 0.65), whereas those with bithiophene moiety led to decreasing of the low quantum yields (ϕF = 0.19 and 0.00). The density‐functional theory (DFT) and time‐dependent–DFT calculations of model compounds corresponding to the polymers were in good agreement with the results from UV–vis properties. The calculations revealed that the electronic structure of the polymer with bithiophene moiety is different from that with biphenyl moiety, and predicted the electron transfer from the bithiophene moiety to the π‐extended quinoline moiety in transition state. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3693–3701, 2010

Polymer reaction of poly(p-phenylene–ethynylene) by addition of decaborane: modulation of luminescence and heat resistance

Polymer reactions of poly(p-phenylene–ethynylene) (PPE) based on the addition reaction of decaborane to the carbon–carbon triple bond were successfully carried out. The platform polymer was synthesized through Sonogashira–Hagihara coupling polymerization. The effective introduction of the boron cluster, and thus the subsequent formation of o-carborane, was supported by 1H and 11B nuclear magnetic resonance spectroscopies. The introduction rate of decaborane to the polymer main chain was proportional to the feed ratio of decaborane. Ultraviolet-visible absorption and photoluminescence studies illustrate the shortening of the effective π-conjugation length caused by the introduction of carborane clusters. Furthermore, the introduction of the boron cluster by the polymer reaction efficiently enhanced the heat resistance of PPE.