Synthesis, characterization and X-ray structures of N-heterocyclic carbene palladium complexes based on calix[4]arenes: highly efficient catalysts towards Suzuki–Miyaura cross-coupling reactions

Narrowly-Distributed Conjugated Polymers Synthesized through Suzuki Polymerization with Palladium(II) N-Heterocyclic Carbene Complex Confined in Dendritic Mesoporous Silica Nanoparticles

A catalytic heterogenous Suzuki polymerization method was developed by confining the Pd(II)-catalyzed cross coupling reactions to take place exclusively in the nanochannels of dendritic mesoporous silica nanoparticles. Conjugated polymers with various monomer combinations, including donor-acceptor structures, were obtained in high yields. The molecular weights of the obtained polymers were well controlled with narrow molecular weight distributions (PDI value down to 1.13). All the polymeric products were highly soluble in common organic solvents, granting them with high processability. All the features of this confined Suzuki polymerization method endow the conjugated polymers great potential in optoelectronic applications.

Efficient in situ N-heterocyclic carbene palladium(ii) generated from Pd(OAc)2 catalysts for carbonylative Suzuki coupling reactions of arylboronic acids with 2-bromopyridine under inert conditions leading to unsymmetrical arylpyridine ketones: synthesis, characterization and cytotoxic activities

N,N-Substituted benzimidazole salts were successfully synthesized and characterized by 1H-NMR, 13C {1H} NMR and IR techniques, which support the proposed structures. Catalysts generated in situ were efficiently used for the carbonylative cross-coupling reaction of 2 bromopyridine with various boronic acids. The reaction was carried out in THF at 110 °C in the presence of K2CO3 under inert conditions and yields unsymmetrical arylpyridine ketones. All N,N-substituted benzimidazole salts 2a-i and 4a-i studied in this work were screened for their cytotoxic activities against human cancer cell lines such us MDA-MB-231, MCF-7 and T47D. The N,N-substituted benzimidazoles 2e and 2f exhibited the most cytotoxic effect with promising cytotoxic activity with IC50 values of 4.45 μg mL-1 against MDA-MB-231 and 4.85 μg mL-1 against MCF7 respectively.

Coordination chemistry of a calix[4]arene-based NHC ligand: dinuclear complexes and comparison to I(i)Pr2Me2

The preparation and coordination chemistry of 5,17-bis(3-methyl-1-imidazol-2-ylidene)-25,26,27,28-tetrapropoxycalix[4]arene (1) is described. Starting from the bis(imidazolium) pro-ligand 1·2HI, the free carbene 1 was readily generated in solution through deprotonation using K[O(t)Bu] and its reactivity with rhodium(i) dimers [Rh(COD)Cl]2 (COD = 1,5-cyclooctadiene) and [Rh(CO)2Cl]2 investigated. Dinuclear complexes were isolated in both cases, where the calix[4]arene-based NHC ligand adopts a bridging μ(2)-coordination mode, and in one case characterised in the solid-state by X-ray diffraction. Using instead an isolated and well-defined (mononuclear) silver transfer agent, generated by reaction of 1·2HI with Ag2O in the presence of a halide extractor, reactions with [Rh(COD)Cl]2 and [Rh(CO)2Cl]2 produced cationic dinuclear complexes bearing μ(2)-1 and μ(2)-Cl bridging ligands. The structural formulation of the novel dinuclear adducts of 1 was aided through spectroscopic congruence with model complexes, containing monodentate 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (I(i)Pr2Me2).

Structures of potassium calix[4]arene crown ether inclusion complexes and application in polymerization of rac-lactide

Reaction of 1,3-dipropoxy-p-tert-butyl-calix[4]arene (L(1)H2) with KN(SiMe3)2 afforded a one-dimensional (1D) chain complex [K2L(1)]n (1). Upon reaction with 1 equivalent 18-crown-6, complex 1 can convert to complex [K2(18-crown-6)L(1)] (2) which possesses a sandwich structure. Treatment of two calix[4]arene-crown ligands of 1,3-dihydroxy-p-tert-butyl-calix[4]arene-crown-5 (L(2)H2) and 1,2-dihydroxy-p-tert-butyl-calix[4]arene-crown-5 (L(3)H2) with KN(SiMe3)2 gave the dinuclear complex [K2L(2)] (3) and the mononuclear complex [K(THF)L(3)H] (4), respectively. Complexes 1-4 were all characterized by single-crystal X-ray diffraction techniques. The variable temperature (1)H NMR spectrum indicates there is a quick rotation equilibrium of the two phenoxy groups in complex 3. In addition, complexes 1-4 have been tested for the ring-opening polymerization (ROP) of rac-lactide and the results showed that complexes 2 and 3 are highly active for the ROP of rac-lactide. The obtained polymers displayed low dispersity values (Đ) and the molecular weights are close to the calculated ones. Furthermore, complexes 2 and 3 show moderate isoselectivities of Pm = 0.67 and Pm = 0.73, respectively.

Copper complexes bearing an NHC–calixarene unit: synthesis and application in click chemistry

Novel N-heterocyclic carbene (NHC) copper complexes supported by calix[4]arene were synthesized and showed good catalytic activity when applied in click chemistry.

Palladium(0)-mediated C–H bond activation of N-(naphthyl)salicylaldimine and related ligands: utilization of the resulting organopalladium complexes in catalytic C–C and C–N coupling reactions

Aldimine ligands undergo palladium(0) mediated C–H bond activation to afford cyclopalladated complexes, which efficiently catalyze C–C and C–N coupling.