Non-Sonogashira-type palladium-catalyzed coupling reactions of terminal alkynes assisted by silver(I) oxide or tetrabutylammonium fluoride

Diastereoselective Self-Assembly of Low-Symmetry Pdn L2n Nanocages through Coordination-Sphere Engineering

Metal-organic cages (MOCs) are popular host architectures assembled from ligands and metal ions/nodes. Assembling structurally complex, low-symmetry MOCs with anisotropic cavities can be limited by the formation of statistical isomer libraries. We set out to investigate the use of primary coordination-sphere engineering (CSE) to bias isomer selectivity within homo- and heteroleptic Pdn L2n cages. Unexpected differences in selectivities between alternative donor groups led us to recognise the significant impact of the second coordination sphere on isomer stabilities. From this, molecular-level insight into the origins of selectivity between cis and trans diastereoisomers was gained, highlighting the importance of both host-guest and host-solvent interactions, in addition to ligand design. This detailed understanding allows precision engineering of low-symmetry MOC assemblies without wholesale redesign of the ligand framework, and fundamentally provides a theoretical scaffold for the development of stimuli-responsive, shape-shifting MOCs.

Efficient access to materials-oriented aromatic alkynes via the mechanochemical Sonogashira coupling of solid aryl halides with large polycyclic conjugated systems

Sonogashira coupling represents an indispensable tool for the preparation of organic materials that contain C(sp)-C(sp2) bonds. Improving the efficiency and generality of this methodology has long been an important research subject in materials science. Here, we show that a high-temperature ball-milling technique enables the highly efficient palladium-catalyzed Sonogashira coupling of solid aryl halides that bear large polyaromatic structures including sparingly soluble substrates and unactivated aryl chlorides. In fact, this new protocol provides various materials-oriented polyaromatic alkynes in excellent yield within short reaction times in the absence of bulk reaction solvents. Notably, we synthesized a new luminescent material via the mechanochemical Sonogashira coupling of poorly soluble Vat Red 1 in a much higher yield compared to those obtained using solution-based conditions. The utility of this method was further demonstrated by the rapid synthesis of a fluorescent metal-organic framework (MOF) precursor via two sequential mechanochemical Sonogashira cross-coupling reactions. The present study illustrates the great potential of Sonogashira coupling using ball milling for the preparation of materials-oriented alkynes and for the discovery of novel functional materials.

Saccharide-Functionalized Poly(Zn-salphen)-alt-(m- and p-phenyleneethynylene)s as Dynamic Helical Metallopolymers

The study of metallopolymers with controllable helical sense remains in its infancy. We report arabinose-functionalized (Zn-salphen)-based conjugated polymers that display mirror-image circular dichroism spectra for L- and D-sugar sidechains respectively, signifying ordered (helical) coiling of the polymer backbone with opposite screw-sense preferences. The observation of different spectroscopic behavior and Cotton effects for a variety of solvents (in a reversible manner) and temperatures, ascribed to changes in the extent of intrachain (Zn⋅⋅⋅O(salphen) and π-stacking) interactions between Zn-salphen moieties, thus indicate the flexible, responsive and dynamic nature of the folded helical conformation in these systems. An application study signifying that activity can be governed by the structure and helical sense of the polymer is described.

NHC-Mediated Synthesis of Tricyclic Spirocarbocycles via an Intramolecular Stetter Reaction of Cyclic Enal-Enones

A general and efficient method for the synthesis of tricyclic spirocarbocycles is described. Various cyclic enal-enones were reacted with an N-heterocyclic carbene, and an intramolecular Stetter reaction proceeded smoothly to give various tricyclic spiro-1,4-diketones in 31-72% yields. The ring size of the spiro compounds can be easily controlled using different cyclic enals and enones or by altering the length of the carbon tether.

Calcium carbide catalytically activated with tetra-n-butyl ammonium fluoride for Sonogashira cross coupling reactions

We report a novel method for the direct synthesis of mono- and bis-arylated alkynes utilizing catalytically activated CaC₂ as the alkyne component.

A dramatic enhancing effect of InBr3 towards the oxidative Sonogashira cross-coupling reaction of 2-ethynylanilines

The addition of InBr3 to the oxidative Sonogashira cross-coupling reaction of 2-ethynylaniline with (E)-trimethyl(3,3,3-trifluoroprop-1-enyl)silane led to a dramatic increase in the reactivity to afford the corresponding 1,3-enynes bearing a trifluoromethyl group on their terminal sp(2) carbon. The subsequent cyclization of these 1,3-enynes under palladium catalysis provides access to the corresponding indoles bearing a 3,3,3-trifluoroprop-1-enyl group at their 2-position.

Formal Gold-to-Gold Transmetalation of an Alkynyl Group Mediated by Palladium: A Bisalkynyl Gold Complex as a Ligand to Palladium

The reaction of [Au(C≡C-n-Bu)]n with [Pd(η(3) -allyl)Cl(PPh3 )] results in a ligand and alkynyl rearrangement, and leads to the heterometallic complex [Pd(η(3) -allyl){Au(C≡C-n-Bu)2 }]2 (3) with an unprecedented bridging bisalkynyl-gold ligand coordinated to palladium. This is a formal gold-to-gold transmetalation that occurs through reversible alkynyl transmetalations between gold and palladium.

A highly efficient copper and ligand free protocol for the room temperature Sonogashira reaction

A mild and efficient catalytic system based on PdCl₂ and Na₂SO₄ has been developed for the Sonogashira reaction of aryl iodides at room temperature.

A palladium salen complex: an efficient catalyst for the Sonogashira reaction at room temperature

A tetradentate Schiff base derived palladium complex works as an efficient catalyst for the room temperature Sonogashira reaction.

Silver salts and DBU cooperatively catalyzed nucleophilic addition/cyclization of propargylic alcohols with trifluoromethyl ketones

A general and efficient synthesis of trifluoromethyl substituted 5-alkylidene-1,3-dioxolane using a silver salt and DBU cooperatively catalyzed nucleophilic addition/cyclization of propargylic alcohols and trifluoromethyl ketones is described.

π-Extension of a 4-ethoxy-1,3-thiazole via aryl alkyne cross coupling: synthesis and exploration of the electronic structure

π-Extension of 4-ethoxy-1,3-thiazolesviaaryl coupling resulted in a twofold increase of molar extinction coefficients and larger Stokes’ shifts.

Palladium-catalyzed oxidative deacetonative coupling of 4-aryl-2-methyl-3-butyn-2-ols with H-phosphonates

A new and generally practical synthesis of alkynylphosphonates through a palladium-catalyzed consecutive Sonogashira/deacetonative process using aryl bromides, 2-methyl-3-butyn-2-ol and H-phosphonates is developed.

An organo-NHC catalyzed domino addition approach for the selective synthesis of 5-butynylisoxazoles and subsequent Sonogashira coupling

An organo-NHC catalysed domino addition approach for the selective synthesis of 5-butynylisoxazoles and the subsequent Sonogashira cross-coupling for the selective synthesis of corresponding internal alkynes is described.

Molecular stirrers in action

A series of first-generation light-driven molecular motors with rigid substituents of varying length was synthesized to act as "molecular stirrers". Their rotary motion was studied by (1)H NMR and UV-vis absorption spectroscopy in a variety of solvents with different polarity and viscosity. Quantitative analyses of kinetic and thermodynamic parameters show that the rotary speed is affected by the rigidity of the substituents and the length of the rigid substituents and that the differences in speed are governed by entropy effects. Most pronounced is the effect of solvent viscosity on the rotary motion when long, rigid substituents are present. The α values obtained by the free volume model, supported by DFT calculations, demonstrate that during the rotary process of the motor, as the rigid substituent becomes longer, an increased rearranging volume is needed, which leads to enhanced solvent displacement and retardation of the motor.

Bursting photosynthesis: designing ad-hoc fluorophores to complement the light harvesting capability of the photosynthetic reaction center

The covalent functionalization of photosynthetic proteins with properly tailored organic molecular antennas represents a powerful approach to build a new generation of hybrid systems capable of exploiting solar energy. In this paper the strategy for the synthesis of the tailored aryleneethynylene organic fluorophore (AE) properly designed to act as light harvesting antenna is presented along with its successful bioconjugation to the photosynthetic reaction center RC from the bacterium Rhodobacter sphaeroides .

Silver-mediated palladium-catalyzed direct C-H arylation of 3-bromoisothiazole-4-carbonitrile

Silver(I) fluoride-mediated Pd-catalyzed C-H direct arylation/heteroarylation of 3-bromoisothiazole-4-carbonitrile (1a) gives twenty-four 5-aryl/heteroaryl-3-bromoisothiazole-4-carbonitriles. The reaction was partially optimized with respect to catalyst, ligand, and base. During this study 3,3'-dibromo-5,5'-biisothiazole-4,4'-dicarbonitrile (3a) was isolated as a byproduct and subsequently prepared via the silver-mediated Pd-catalyzed oxidative dimerization of 3-bromoisothiazole-4-carbonitrile in 67% yield. The analogous phenylation and oxidative dimerization of 3-chloroisothiazole-4-carbonitrile (1b) gave 3-chloro-5-phenylisothiazole-4-carbonitrile (4) and 3,3'-dichloro-5,5'-biisothiazole-4,4'-dicarbonitrile (3b) in 96% and 69% yields, respectively.

Acetylene-based materials in organic photovoltaics

Fossil fuel alternatives, such as solar energy, are moving to the forefront in a variety of research fields. Organic photovoltaic systems hold the promise of a lightweight, flexible, cost-effective solar energy conversion platform, which could benefit from simple solution-processing of the active layer. The discovery of semiconductive polyacetylene by Heeger et al. in the late 1970s was a milestone towards the use of organic materials in electronics; the development of efficient protocols for the palladium catalyzed alkynylation reactions and the new conception of steric and conformational advantages of acetylenes have been recently focused the attention on conjugated triple-bond containing systems as a promising class of semiconductors for OPVs applications. We review here the most important and representative (poly)arylacetylenes that have been used in the field. A general introduction to (poly)arylacetylenes, and the most common synthetic approaches directed toward making these materials will be firstly given. After a brief discussion on working principles and critical parameters of OPVs, we will focus on molecular arylacetylenes, (co)polymers containing triple bonds, and metallopolyyne polymers as p-type semiconductor materials. The last section will deal with hybrids in which oligomeric/polymeric structures incorporating acetylenic linkages such as phenylene ethynylenes have been attached onto C₆₀, and their use as the active materials in photovoltaic devices.