NHC-Ligand Effectiveness in the Fluorine-Free Hiyama Reaction of Aryl Halides

1-Benzyl-3-(2-hydroxy-2-phenylethyl)imidazolium chloride (5), which is a precursor of an N-heterocyclic carbene ligand, in combination with palladium acetate, has been employed as an effective catalyst for the fluorine-free Hiyama reaction. A systematic study of the catalytic mixture, by a 32 factorial design, has revealed that both the amount of palladium and the Pd/NHC precursor ratio are important factors for obtaining good yields of the coupling products, indicating an interaction between them. The best catalytic system involves mixing 0.1 mol-% palladium acetate in a 1:5 ratio (Pd/salt 5), which allows the effective coupling of a range of aryl bromides and chlorides with trimethoxy(phenyl)silane. The Hiyama reactions are carried out in NaOH solution (50 % H2O w/w), at 120 °C under microwave irradiation during 60 min.

Palladium(II) complexes with a phosphino-oxime ligand: synthesis, structure and applications to the catalytic rearrangement and dehydration of aldoximes

The treatment of [PdCl2(COD)] (COD = 1,5-cyclooctadiene) with 1 and 2 equivalents of 2-(diphenylphosphino)benzaldehyde oxime in dichloromethane at room temperature led to the selective formation of [PdCl2{κ2-(P,N)-2-Ph2PC6H4CH[double bond, length as m-dash]NOH}] (1) and [Pd{κ2-(P,N)-2-Ph2PC6H4CH[double bond, length as m-dash]NOH}2][Cl]2 (2), respectively, which represent the first examples of Pd(II) complexes containing a phosphino-oxime ligand. These compounds, whose structures were fully confirmed by X-ray diffraction methods, were active in the catalytic rearrangement of aldoximes. In particular, using 5 mol% complex 1, a large variety of aldoximes could be cleanly converted into the corresponding primary amides at 100 °C, employing water as solvent and without the assistance of any cocatalyst. Palladium nanoparticles are the active species in the rearrangement process. In addition, when the same reactions were performed employing acetonitrile as solvent, selective dehydration of the aldoximes to form the respective nitriles was observed. For comparative purposes, the catalytic behaviour of an oxime-derived palladacyclic complex has also been briefly evaluated.

Gold Nanoparticles Supported on Polyacrylamide Containing a Phosphorus Ligand as an Efficient Heterogeneous Catalyst for Three-Component Synthesis of Propargylamines in Water

Gold nanoparticles supported on a polyacrylamide containing a phosphinite ligand have been synthesized and characterized using different techniques such as TEM, SEM, EDX, XPS, and solid UV analyses. The new material was successfully applied as a heterogeneous catalyst for the three-component A3 coupling of amines, aldehydes, and alkynes to give propargylamines. Reactions are performed in neat water at 80 °C with only 0.05 mol% catalyst loading. The heterogeneous catalyst is recyclable during seven consecutive runs with small decrease in activity.

Ligand-Free Palladium-Catalyzed Oxyarylation of Dihydronaphthal­enes and Chromenequinone with o-Iodophenols and 3-Iodolawsone in PEG-400: An Efficient Synthesis of 5-Carbapterocarpans and Pterocarpanquinones

Dihydronaphthalenes were oxyarylated with o-iodophenols, in PEG-400 at 140 or 170 °C, leading regio- and stereoselectively to 5-carbapterocarpans. By using Pd(OAc)2 (5–10 mol%) as precatalyst and Ag2CO3 (1.1 equiv) as base (conditions A), products were obtained in good to excellent chemical yields, in 5–30 minutes, irrespective of the pattern of substitution the starting materials. Alternatively, when p-hydroxyacetophenone oxime derived palladacycle (1 mol%) was used as precatalyst, and dicyclohexylamine (2 equiv) was used as base (silver-free, conditions B), the corresponding adducts were obtained in moderate to good yields, in 0.5 to 4 hours. Finally, the oxyarylation of dihydronaphthalenes­ and chromenquinone with o-iodophenols and 3-iodolawsone in PEG-400 under conditions A led regio- and stereoselectively to the formation of carbapterocarpanquinones and pterocarpanquinones in moderate yield.