Structure, dynamics and catalytic activity of palladium(II) complexes with imidazole ligands

The Influence of Ligands on the Pd-Catalyzed Diarylation of Vinyl Esters

The impact of ligands on the palladium-catalyzed 1,2-diarylation reaction course is presented. The application of Pd-dmpzc as a catalyst provides an efficient, chemoselective and sustainable protocol for the synthesis of valuable 1,2-diphenylethyl acetates. The reaction is conducted in water under mild conditions. Reaction products can be easily separated from the reaction mixture and catalyst by simple extraction. What is more, the rational choice of catalyst significantly reduces the leaching of the metal into the product and its contamination (0.1 ppm). Efficient phase separation and ultralow Pd leaching enable the reuse of the water medium containing the Pd-dmpzc catalyst several times without a significant loss of activity and with even higher selectivity (from 95% to 100% in the third cycle). The recyclability of both the catalyst and the reaction medium together with high chemoselectivity and low palladium leaching reduces the amount of waste and the cost of the process, exhibiting an example of a sustainable and green methodology.

Evidence for a Cooperative Mechanism Involving Two Palladium(0) Centers in the Oxidative Addition of Iodoarenes

Oxidative addition of iodoarenes (ArI) to Pd⁰ ligated by 1-methyl-1H-imidazole (mim) in polar solvents leads to cationic arylpalladium(II) complexes [ArPd(mim)₃ ]⁺ . Kinetic analyses evidence that this reaction is second order with respect to the concentration of Pd⁰ , and a mechanism involving the cooperative intervention of two Pd⁰ centers has been postulated to explain this finding. This unusual behavior is also observed with other nitrogen-containing ligands and it is general for iodobenzenes substituted with electron-donating or weakly electron-withdrawing groups. In contrast, bromoarenes and electron-poor iodoarenes display first-order kinetics with respect to Pd⁰ . Theoretical calculations performed at the density functional theory (DFT) level suggest the existence of mim-ligated ArI-Pd⁰ complexes, in which the iodoarene is bound to the metal in a halogen-bond-like fashion. Coordination weakens the C-I bond and facilitates the oxidative insertion of another Pd⁰ center across this C-I bond. This conceptually novel mechanism, involving the cooperative participation of two distinct metal centers, allows a full explanation of the experimentally observed kinetics.

Regioselective C–H alkenylation of imidazoles and its application to the synthesis of unsymmetrically substituted benzimidazoles

A palladium-catalyzed C5-selective alkenylation of imidazoles has been developed and applied to the synthesis of alkenyl imidazoles and multi-substituted benzimidazoles.

Palladium nanoparticles generated in situ used as catalysts in carbonylative cross-coupling in aqueous medium

Pd NPs, obtained in situ from imidazole complexes Pd(im)₂Cl₂ (im = methylimidazole, butylimidazole), efficiently catalyze the carbonylative Suzuki coupling in water at 80 °C and 1 atm of CO.

PdCl2(1-methylimidazole)2-catalysed Suzuki–Miyaura and Mizoroki–Heck Reactions Performed in Neat Water

PdCl2(1-methylimidazole)2 was an effective catalyst in neat water for the Suzuki–Miyaura and Mizoroki–Heck reactions of aryl bromides and iodides with, respectively, arylboronic acids and acrylic acid. Under optimal conditions, the products, variously substituted biphenyls and monosubstituted trans-cinnamic acids, respectively, were formed in good to almost quantitative yields.

FT-IR and Raman spectroscopic and quantum chemical investigations of some metal halide complexes of 1-phenylpiperazine

New metal halide complexes in the form of M(pp)(2)Cl(2) (where pp=1-phenylpiperazine and M=Pd or Hg) have been prepared for the first time and their FT-IR and FT-Raman spectra are reported in the region of 4000-10 cm(-1) and 4000-50 cm(-1), respectively. The optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of the present compounds are theoretically examined by means of B3LYP hybrid density functional theory (DFT) method together with Lanl2dz basis set. Furthermore, reliable vibrational assignments made on the basis of potential energy distribution (PED) were calculated and the thermodynamics functions, the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO) of these compounds have been predicted. According to the results, theoretical values have been successfully compared against experimental data.

Highly selective reactions of unbiased alkenyl halides and alkylzinc halides: Negishi-Plus couplings

High yielding stereo- and chemoselective Pd-catalyzed cross-couplings in THF at room temperature of alkenyl iodides and bromides with primary and secondary alkyl zinc iodides have been developed with the aid of N-methyimidazole as the key additive.