Palladium Pyridine Research Articles

Zwitterionic Palladium Complexes: Room-Temperature Suzuki–Miyaura Cross-Coupling of Sterically Hindered Substrates in an Aqueous Medium

A series of new imidazolium chlorides were straightforwardly prepared from the reactions between chloroacetone and imidazole derivatives. Deprotonation of the methylene proton next to the ketone group in these salts by pyridine led to the formation of a monodentate ligand that coordinated to palladium, readily forming zwitterionic anionic palladium pyridine complexes bearing a formal positive charge on the ligand ancillary. The pyridine ligand in the zwitterionic complexes can be facilely replaced by phosphine ligands. Seven of these new complexes were successfully characterized by X-ray crystallography. The zwitterionic phosphine complexes were highly efficient in catalyzing room-temperature Suzuki–Miyaura reactions between sterically hindered aryl chlorides and arylboronic acids in an aqueous medium.

Suzuki cross-coupling reaction over a palladium–pyridine complex immobilized on hydrotalcite

A catalyst consisting of a Pd(II) complex immobilized on the surface of a layered double hydroxide (LDH) was prepared. The Pd–LDH complex proved effective in the Suzuki cross-coupling reaction under very mild conditions (viz. a temperature of 55 °C and atmospheric pressure); in fact, it provided conversion and selectivity results surpassing those of existing heterogeneous phase catalysts and most homogeneous phase catalysts for the same purpose. The support and the active phase of the catalyst were characterized by using various instrumental techniques including X-ray diffraction and NMR spectroscopy. Of the inorganic bases used in combination with the catalyst, potassium carbonate was found to provide the best results in the reaction.

ChemInform Abstract: Enantioselective Diene Cyclization/Hydrosilylation Catalyzed by Optically Active Palladium Bisoxazoline and Pyridine-Oxazoline Complexes.

A 1:1 mixture of (N−N)Pd(Me)Cl [N−N = (S,S)-4,4‘-dibenzyl-4,5,4‘,5‘-tetrahydro-2,2‘-bisoxazoline] (S,S-4a) and NaBAr4 [Ar = 3,5-C6H3(CF3)2] (5 mol %) catalyzed the asymmetric cyclization/hydrosilylation of dimethyl diallylmalonate (2) and triethylsilane at −30 °C for 48 h to form an 8.1:1 mixture of the silylated carbocycle (S,S)-trans-1,1-dicarbomethoxy-4-methyl-3-[(triethylsilyl)methyl]cyclopentane (S,S-3) (95% de, 72% ee) and dimethyl 3,4-dimethylcyclopentane-1,1-dicarboxylate (S,S-6) in 64% combined yield. In comparison, a 1:1 mixture of the palladium pyridine−oxazoline complex (N−N)Pd(Me)Cl [N−N = (R)-(+)-4-isopropyl-2-(2-pyridinyl)-2-oxazoline] (R-5b) and NaBAr4 (5 mol %) catalyzed the asymmetric cyclization/hydrosilylation of 2 and triethylsilane at −32 °C for 24 h to form carbocycle S,S-3 in 82% yield (>95% de, 87% ee) as the exclusive product. Asymmetric diene cyclization catalyzed by complex R-5b was compatible with a range of functional groups and produced carbocycles with up to 91% ee. The pro...

Enantioselective diene Cyclization/Hydrosilylation catalyzed by optically active palladium bisoxazoline and pyridine-oxazoline complexes.

A 1:1 mixture of (N-N)Pd(Me)Cl ¿N-N = (S,S)-4,4'-dibenzyl-4,5,4', 5'-tetrahydro-2,2'-bisoxazoline (S,S-4a) and NaBAr(4) ¿Ar = 3, 5-C(6)H(3)(CF(3))(2) (5 mol %) catalyzed the asymmetric cyclization/hydrosilylation of dimethyl diallylmalonate (2) and triethylsilane at -30 degrees C for 48 h to form an 8.1:1 mixture of the silylated carbocycle (S,S)-trans-1, 1-dicarbomethoxy-4-methyl-3-¿(triethylsilyl)methylcyclop ent ane (S, S-3) (95% de, 72% ee) and dimethyl 3,4-dimethylcyclopentane-1, 1-dicarboxylate (S,S-6) in 64% combined yield. In comparison, a 1:1 mixture of the palladium pyridine-oxazoline complex (N-N)Pd(Me)Cl ¿N-N = (R)-(+)-4-isopropyl-2-(2-pyridinyl)-2-oxazoline (R-5b) and NaBAr(4) (5 mol %) catalyzed the asymmetric cyclization/hydrosilylation of 2 and triethylsilane at -32 degrees C for 24 h to form carbocycle S,S-3 in 82% yield (>95% de, 87% ee) as the exclusive product. Asymmetric diene cyclization catalyzed by complex R-5b was compatible with a range of functional groups and produced carbocycles with up to 91% ee. The procedure also tolerated substitution at a terminal olefinic position and at the allylic position of the diene.

Asymmetric Cyclization/Hydrosilylation of Functionalized 1,6-Dienes Catalyzed by Enantiomerically Pure Palladium Pyridine−Oxazoline Complexes

Asymmetric Cyclization/Hydrosilylation of Functionalized 1,6-Dienes Catalyzed by Enantiomerically Pure Palladium Pyridine−Oxazoline Complexes

Gravimetric, volumetric and conductometric determination of palladium with pyridine

Palladium has been determined gravimetrically as palladium pyridine iodide complex, volumetrically as palladium pyridine iodide and palladium pyridine thiocyanate complex and conductometrically as palladium pyridine iodide, thiocyanate, azide and dichromate. Advantages of the different methods and interferences of various ions have been discussed in each case. Determination is possible in the presence of Pt, Rh, Ru, Ir and Os.