Search results for "Palladium"

Studien zum Vorgang der Wasserstoffübertragung, 57 Einige Beispiele zur diastereoselektiven Hydrierung von Verbindungen mit prochiralen CC-Bindungen

1979

(1R,2S)-N,N-Dimethylephedriniumchlorid, (1S,2S)-N,N-Dimethylpseudoephedriniumchlorid, (1R,2S)-N-Methylephedrin, (1S,2S)-N-Methylpseudoephedrin und [(2S)-2-Hydroxy-2-phenyl-ethyl]trimethylammoniumchlorid werden mit α- und β-Methylzimtsaure zu 1–4 und 7 verestert und an Raney-Nickel, Palladium, Platin und einer Reihe von Edelmetalltragerkatalysatoren hydriert. Die hydrierten Ester werden verseift und die optische Ausbeute der α- bzw. β-Methyldihydrozimtsaure bestimmt. Die optischen Ausbeuten bewegen sich in Abhangigkeit von der optisch aktiven Hilfskomponente zwischen 68 und 4%. Bei optischen Ausbeuten uber 10% wird die absolute Konfiguration der α- oder β-Methyldihydrozimtsaure von der Konfi…

Palladium-Catalyzed C-C Ring Closure in α-Chloromethylimines: Synthesis of 1H -Indoles

2018

A Cation-Captured Palladium(0) Anion: Synthesis, Structure, and Bonding of [PdBr(PPh3)2]− Ligated by an N-Heterocyclic Phosphenium Cation

2009

Unsaturated N-heterocyclic phosphenium cations (uNHP) stabilize the [Pd0(PR3)2X]− anion proposed over the past decade to be the crucial but elusive intermediate in palladium-catalyzed cross-coupling reactions (X = halide). Insertion of metal into the P−Br bond of the precursor mesityl-substituted bromophosphine gives the structurally characterized Pd(0)-phosphenium complex (uNHPMes)Pd(PPh3)2Br, which features a long Pd−Br bond (2.7240(9) A) and the shortest known Pd−P bond (2.1166(17) A). The reaction is proposed to proceed by an associative pathway involving a Pd-bromophosphine complex that undergoes P-to-Pd bromide transfer.

Optical, Electrochemical, and Catalytic Properties of the Unsaturated Host Pd3(dppm)3(CO)2+and Pd4(dppm)4(H)2+2Clusters: An Overview

2004

This paper presents an overview of the optical, photophysical, and photochemical properties including UV-visible and luminescence spectra in solution at 298 and 77 K, along with electrochemical, and catalytic behavior under reduction conditions (for both thermally and electrochemically assisted systems) of the tri- and tetranuclear Pd3(dppm)3(CO)2+ and Pd4(dppm)4(H)2+ 2 clusters (dppm=bis(diphenylphosphino)methane). This review is also complemented with relevant information about their syntheses, molecular and electronic structures supported from computer modeling, EHMO and DFT calculations, and their host-guest behavior with anions and neutral molecules, in relation with their observed rea…

Heterogeneous vs Homogeneous Palladium Catalysts for Cross-Coupling Reactions

2012

A large number of immobilized-Pd-catalysts for cross-coupling reactions have been introduced in the last decade. Are the observed catalyzed reactions truly heterogeneous or are they homogeneous due to leached palladium? This account critically addresses the leaching issue by selectively referring to some of the newly developed catalytic systems in an attempt to evaluate said systems based on uniform criteria. The report is concluded by identifying the relevant chemical and structural challenges in the field.

Synthesis, solution behaviour and potential anticancer activity of new trinuclear organometallic palladium(II) complex of S-1-phenylethyl dithiooxami…

2019

Abstract Addition of H2R2DTO (R = {S}-1-phenylethyl and DTO = dithiooxamide) to the bis(benzonitrile)palladium(II) chloride complex in chloroform afforded the mononuclear Pd(DTO)2·2HCl complex. The complex treated with NaHCO3 for removing of HCl and then reacted with [Pd(ƞ3-allyl)(µ-Cl)]2 for preparation of a new trimetallic organopalladium(II) complex. The molecular structure of the trimetallic complex was determined by X-ray diffraction indicating a planar geometry around each palladium center. Also, variable temperature spectroscopy for this complex was performed in CDCl3 in the range 298–390 K, and simulations of the dynamic spectra were performed using the gNMR program. A comparison be…

Improved synthesis of Bn5CpRu(CO)2Cl and its application as racemization catalyst in preparative-scale metalloenzymatic dynamic kinetic resolution of…

2010

An improved gram-scale synthesis of Bn5CpRu(CO)2Cl is reported based on heating of pentabenzylcyclopentadiene with Ru3(CO)12 at 160 °C under argon atmosphere in mesitylene followed by addition of chloroform, continued heating, and evaporation of the solvents. Subsequent washing of unreacted ligand precursor with hexane provided pure title compound in 77 % yield. In combination with Candida antarctica lipase B (CAL-B) (Novozym 435), this complex forms a highly active racemization catalyst for metallo-enzymatic dynamic kinetic resolution (DKR) of secondary alcohols as demonstrated in the present work by converting 100 g of racemic 1-phenylethanol to (R)-1-phenylethanol in >99 % ee and 93 %…

Biogenic synthesis of palladium nanoparticles using Pulicaria glutinosa extract and their catalytic activity towards the Suzuki coupling reaction.

2014

Green synthesis of nanomaterials finds the edge over chemical methods due to its environmental compatibility. Herein, we report a facile and eco-friendly method for the synthesis of palladium (Pd) nanoparticles (NPs) using an aqueous solution of Pulicaria glutinosa, a plant widely found in a large region of Saudi Arabia, as a bioreductant. The as-prepared Pd NPs were characterized using ultraviolet-visible (UV-vis) spectroscopy, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transform-infrared spectroscopy (FT-IR). The hydroxyl groups of the plant extract (PE) molecules were found mainly responsible for the red…

Preparation of Pd coated anodic alumina membranes for gas separation media

2007

Different procedures of Pd electroless deposition onto anodic alumina membranes were investigated to form a dense metal layer covering pores. The main difficulty was related to the amorphous nature of anodic alumina membranes, determining low chemical stability in solutions at pH > 9, where Pd plating works more efficiently. As a consequence, it was necessary to find the operative conditions allowing Pd deposition without damaging the membrane: to reduce alumina dissolution, the plating bath was buffered at pH 8.5 by addition of either NaHCO 3 or Na 2 B 4 O 7 ·H 2 O. Acceptable conversion of Pd was found after a deposition time of 3 min. Single and multiple deposition steps (each lasting 3 …

Chiral self-sorting behaviour of [2.2]paracyclophane-based bis(pyridine) ligands

2019

Two constitutionally isomeric chiral bis(pyridine) ligands based on planar chiral 4,15-difunctionalized [2.2]paracyclophanes were synthesized, the respective enantiomers were separated via HPLC on a chiral stationary phase, and their self-assembly behaviour upon coordination to palladium(ii) ions was studied with regard to chiral self-sorting effects. As proven by NMR spectroscopy, mass spectrometry, CD spectroscopy, UV-Vis spectroscopy and X-ray crystallography both ligands form the expected dinuclear complexes upon coordination to cis-protected di- or tetravalent palladium(ii) ions, respectively, however, with distinct differences concerning their chiral self-sorting ability. peerReviewed