Pd-catalyzed Sonogashira Cross-coupling Reaction Research Articles

Aryl-substituted symmetrical and unsymmetrical benzothiadiazoles

The incorporation of a planar anthracene unit lowers the HOMO–LUMO gap and improves the thermal stability of donor–acceptor benzothiadiazoles.

Colorimetric and fluorimetric detection of fluoride and cyanide ions using tri and tetra coordinated boron containing chromophores.

Two organoboron based fluorophores pyrazabole and BODIPY have been designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction and successfully employed for fluoride and cyanide ion sensing. Pyrazabole acts as a fluorimetric sensor, whereas BODIPY acts as a fluorimetric as well as colorimetric sensor for fluoride and cyanide ions with ratiometric response. The photophysical properties of pyrazabole and BODIPY exhibit good electronic communication between triarylborane and pyrazabole/BODIPY. The single crystal X-ray structure of the pyrazabole shows a chair conformation for the pyrazabole core. The packing in pyrazabole and BODIPY shows interesting supramolecular structures. The computational studies show good agreement with the experimental results.

Star shaped ferrocenyl truxenes: synthesis, structure and properties

This article reports the design and synthesis of star shaped, C3-symmetric ferrocenyl substituted truxenes by the Pd-catalyzed Sonogashira cross-coupling and cycloaddition reaction. The single photon absorption and electrochemical properties indicate significant electronic interaction between ferrocene and truxene core. The bathochromic shift in the absorption spectra of truxenes 4a-4c and 5a is a function of enhanced conjugation. The incorporation of tetracyanoethylene (TCNE) results in a strong charge transfer band in truxene 5a. The single crystal structure of truxene 4a is presented, which shows interesting supramolecular interactions.

The quenching of fluorescence as an indicator of donor-strength in meso arylethynyl BODIPYs

A series of meso arylethynyl BODIPYs (2a-2h) were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. The effects of the donor on the photophysical properties of the BODIPYs were explored. The DFT optimized structures and crystal structures show the planar orientation of the donor group with respect to the acceptor BODIPY, which favors a high degree of conjugation and induces strong donor-acceptor interactions. The quenching of fluorescence was correlated with the electron donating strength of the donor. The anthracene, pyrene and triphenylamine were found to have a stronger electron donating ability than the p-methoxyphenyl, phenanthrene, 1-naphthalene, biphenyl, and 2-naphthalene moieties. This was further supported by computational calculations and electrochemical analysis. The single crystal structures of BODIPYs 2d and 2e are reported, which show marvellous supramolecular structures.

Synthesis, photophysical and electrochemical characterization of terpyridine-functionalized dendritic oligothiophenes and their Ru(II) complexes

Pd-catalyzed Sonogashira cross-coupling reactions were used to synthesize novel π-conjugated oligothienylene-ethynylene dendrons and their corresponding terpyridine-based ligands. Their complexation with Ru(II) led to interesting novel metallodendrimers with rich spectroscopic properties. All new compounds were fully characterized by 1H and 13C NMR, as well as MALDI–TOF mass spectra. Density functional theory (DFT) calculations performed on these complexes gave more insight into the molecular orbital distributions. Photophysical and electrochemical studies were carried out in order to elucidate structure–property relationships and the effect of the dendritic structure on the metal complexes. Photophysical studies of the complexes revealed broad absorption spectra covering from 250 to 600 nm and high molar extinction coefficients. The MLCT emission of these complexes were significantly red-shifted (up to 115 nm) compared to the parent [Ru(tpy)2]2+ complex.

Ferrocenyl substituted calixarenes: synthesis, structure and properties

A set of ferrocenyl substituted calix[4]arenes were designed and synthesized by the Pd-catalyzed Sonogashira cross coupling reaction. The photophysical and electrochemical data show a substantial electronic interaction between the ferrocene unit and the calixarene core. Calixarenes 5a–5c are non-emissive in nature and the absorption maxima of 5a–5c exhibit a red shifted absorption. The calixarene core exhibits a cone conformation, which was confirmed by 1H NMR and X-ray crystallography. The crystal packing of 5a exhibits a C–H–π bonded 2-D network.

β-Substituted ferrocenyl porphyrins: synthesis, structure, and properties

β-Substituted ferrocenyl porphyrins were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. The UV-vis absorption, emission, and cyclic voltammetric results indicate strong electronic communication between ferrocene and porphyrin. The porphyrin 4a is non-emissive in nature, while 4b and 4c show reduced fluorescence quantum yield. The single crystal X-ray structure of 4b is reported, which shows extensive C-H-π interactions.

Light-Harvesting Cross-Linked Polymers for Efficient Heterogeneous Photocatalysis

Nonporous, phosphorescent cross-linked polymers (Ru-CP and Ir-CP) were synthesized via Pd-catalyzed Sonogashira cross-coupling reactions between tetra(p-ethynylphenyl)methane and dibrominated Ru(bpy)(3)(2+) or Ir(ppy)(2)(bpy)(+), respectively. The resultant particulate cross-linked polymer (CP) materials have very high catalyst loadings (76.3 wt % for Ru-CP and 71.6 wt % for Ir-CP), and are nonporous with negligibly small surface areas (2.9 m(2)/g for Ru-CP and 2.7 m(2)/g for Ir-CP). Despite their nonporous nature, the insoluble CP materials serve as highly active and recyclable heterogeneous photocatalysts for a range of organic transformations such as aza-Henry reaction, aerobic amine coupling, and dehalogenation of benzyl bromoacetate. An efficient light-harvesting mechanism, which involves collection of photons by exciting the (3)MLCT states of the phosphors and migration of the excited states to the particle surface, is proposed to account for the very high catalytic activities of these nonporous CPs. Steady-state and time-resolved emission data, as well as the reduced catalytic activity of Os(bpy)(3)(2+)-doped Ru-CPs supports efficient excited state migration for the CP frameworks. This work uncovers a new strategy in designing highly efficient photocatalysts based on light-harvesting cross-linked polymers.

Controlling hydrogen-bond preferences in bipyridines with competing binding sites

The design and synthesis of a family of supramolecular reagents (SRs) based on ethynyl-spaced substituted bipyridines are described, and their potential use as molecular ‘hubs’ for the predictable construction of binary and ternary co-crystals is explored. Each SR was synthesized in good yields through consecutive Pd-catalyzed Sonogashira cross-coupling reactions. Crystal structures of three binary co-crystals are presented with each structure clearly illustrating how accurate supramolecular assembly control can be achieved by increasing/decreasing the strength of the participating hydrogen-bond interactions.

Conjugated Polymer Gels with Dendritic Hydrophilic Side Chains

This paper reports the synthesis and optical properties of poly(p-phenylene ethynylene) gels that features hydrophilic dendritic groups. The conjugated polymer gel particles with hydrophilic side chains have been prepared by a synthetic route that involves initial preparation of an analogue polymer gel having triester side chains through the modified Pd-catalyzed Sonogashira cross-coupling reaction in aqueous emulsion, and the following conversion of ester groups with tris(hydroxymethyl)aminomethane (Tris). The size distribution of the water-swollen particles is relatively narrow with an average diameter of 900 nm. The synthesized particles showed fluorescence and volume changes in response to various solvent compositions.

Poly(p‐phenylene ethynylene)s with Facially Amphiphilic Pendant Groups: Solvatochromism and Supramolecular Assemblies

Novel functionalized poly(p-phenylene ethynylene)s (PPEs) bearing facially amphiphilic cholic and deoxycholic acid units are synthesized by a Pd-catalyzed Sonogashira cross-coupling reaction. Some interesting properties, particularly their optical and self-assembly characteristics, are unraveled. The PPEs that carry bile acid substituents exhibit remarkable solvatochromism in a wide range of solvent systems, and judicious choice of the solvents can adjust the size and morphology of the formed nanoscale supramolecular aggregates. The incorporation of these naturally occurring building blocks can also impart biocompatibility to the conjugated system and stimulate the growth of living cells.

A novel and stereoselective synthesis of 7α-alkynylestra-1,3,5(10)-triene-3,17β-estradiol

Different stereoselective synthetic routes for the preparation of 7α/β-substituted estradiol derivatives, that is, 7α-alkynylestra-1,3,5(10)-triene-3,17β-estradiol (13) and its 17β-acetate derivative (14), are explored. These steroids are key starting materials for Pd-catalyzed Sonogashira cross-coupling reactions to yield potential estrogen receptor (ER) antagonists, ER-based imaging ligands and other multi-functional agents. Initial preparation of 7α-alkynyl nortestosterone derivatives followed by various approaches to aromatize the A-ring, failed. Instead, stereoselective 7α-cyanation before A-ring aromatization, followed by 7α-cyano reduction to the 7α-aldehyde, dibromomethylenation and dehydrobromination of the aldehyde, gave the desired 7α-alkynyl derivatives 13 and 14 in good yield.