Chiral Palladium Complexes Research Articles

ChemInform Abstract: Chiral Pd‐Catalyzed Enantioselective Friedel—Crafts Reaction of Indoles with γ,δ‐Unsaturated β‐Keto Phosphonates.

Abstract The catalytic enantioselective Friedel–Crafts alkylation reaction promoted by chiral palladium complexes is described. The treatment of indoles with γ,δ-unsaturated β-keto phosphonates under the mild reaction conditions afforded the corresponding Friedel–Crafts alkylation adducts with excellent enantioselectivities (up to 99% ee).

Highly enantioselective Friedel–Crafts alkylation of indole and pyrrole with β,γ-unsaturated α-ketoester catalyzed by chiral dicationic palladium complex

The chiral dicationic Pd complexes, bearing sterically demanding diphosphine ligands as Lewis acid catalysts, are shown to catalyze the asymmetric Friedel–Crafts (F–C) alkylations of indoles and pyrroles with β,γ-unsaturated α-ketoesters, to provide the F–C alkylation products with benzylic stereocenters in high yields and enantioselectivities. The reactive chelated structure, formed by the chiral dicationic Pd complex and the electrophile, would be important to gain a high level of asymmetric induction in the F–C alkylation. The F–C products can be readily functionalized to give α-hydroxy esters via catalytic asymmetric ene sequences.

ChemInform Abstract: Catalytic Enantioselective Friedel—Crafts Alkylation of Indoles with β,γ‐Unsaturated α‐Keto Phosphonates in the Presence of Chiral Palladium Complexes.

AbstractOptimized conditions using an air‐ and moisture‐stable chiral Pd‐catalyst are developed for the title reaction.

Friedel-Crafts Alkylation of Indoles Catalyzed by a Chiral Palladium Complex

Friedel-Crafts Alkylation of Indoles Catalyzed by a Chiral Palladium Complex

Fused Indolines by Palladium‐Catalyzed Asymmetric CC Coupling Involving an Unactivated Methylene Group

Selectivity at high temperatures: Bulky, thermally stable, chiral palladium complexes generated from N-heterocyclic carbenes (NHCs; see picture) were successfully applied to the synthesis of highly enantioenriched trans-fused indolines. Remarkably, this reaction occurs at elevated temperatures with excellent asymmetric recognition of an enantiotopic C-H bond in an unactivated methylene unit.

ChemInform Abstract: Catalytic Asymmetric Mannich‐Type Reactions of Fluorinated Ketoesters with N‐Boc Aldimines in the Presence of Chiral Palladium Complexes.

AbstractThe reaction in the presence of BIP allows the access to various biologically interesting synthons with good to excellent enantioselectivity.

Unsymmetrical Chiral PCN Pincer Palladium(II) and Nickel(II) Complexes with Aryl-Based Aminophosphine–Imidazoline Ligands: Synthesis via Aryl C–H Activation and Asymmetric Addition of Diarylphosphines to Enones

Chiral 3-(2′-imidazolinyl)anilines 3a–c were easily synthesized by converting the carboxyl and nitro groups in commercially available 3-nitrobenzoic acid to chiral imidazoline and amine, respectively. The one-pot phosphorylation/metalation reaction of 3-(2′-imidazolinyl)anilines 3a–c, where the amino group in 3a–c was first phosphorylated by reaction with PPh2Cl, followed by metalation with PdCl2 or anhydrous NiCl2 in situ, afforded the three unsymmetrical chiral PCN pincer Pd(II) complexes 4a–c and the Ni(II) complex 5a with aryl-based aminophosphine–imidazoline ligands via aryl C–H bond activation of the related ligands. All of the new compounds were characterized by elemental analysis (HRMS for ligand precursors), 1H and 13C NMR, 31P{1H} NMR (for pincer complexes), and IR spectra. The molecular structures of Pd complexes 4a,c and that of Ni complex 5a have been determined by X-ray single-crystal diffraction. Each complex adopts a typical distorted-square-planar geometry. The potential of the obtained chiral pincers in the asymmetric addition of diarylphosphines to β-substituted enones or trans-β-nitrostyrene was investigated. The Pd pincer 4c, the chirality of which originated from l-phenylglycinol, was found to be an effective catalyst for the asymmetric addition of diphenylphosphine to a series of β-aryl enones with high enantioselectivities (12 examples, 51–94% ee's). In particular, excellent yields and enantioselectivities (>90% yields and ≥90% ee's) were obtained when β-aryl groups in the enones bore an electron-withdrawing group such as p-NO2.

Chiral Pd-catalyzed enantioselective Friedel–Crafts reaction of indoles with γ,δ-unsaturated β-keto phosphonates

The catalytic enantioselective Friedel–Crafts alkylation reaction promoted by chiral palladium complexes is described. The treatment of indoles with γ,δ-unsaturated β-keto phosphonates under the mild reaction conditions afforded the corresponding Friedel–Crafts alkylation adducts with excellent enantioselectivities (up to 99% ee).

Catalytic Enantioselective Friedel-Crafts Alkylation of Indoles with β,γ-Unsaturated α-Keto Phosphonates in the Presence of Chiral Palladium Complexes

The catalytic enantioselective Friedel-Crafts alkylation reaction promoted by chiral palladium complexes is described. The treatment of indoles with β,γ-unsaturated α-keto phosphonates under the mild reaction conditions afforded the corresponding Friedel-Crafts alkylation adducts with excellent enantioselectivities (up to 99% ee).

Synthesis and structural studies of (1R,2R,5R)-chloro{o-[β-(2-hydroxy-2,6,6-trimethylbicyclo[3.1.1]hept-3-ylidenamino)ethyliminomethyl]phenoxy-O,N,N}palladium(II)

The reaction of (1R,2R,5R)-3-[{2-[(2-hydroxybenzylidene)amino]ethyl}imino]-2,6,6-trimethylbicyclo[3.1.1]heptan-2-ol with lithium tetrachloropalladate was studied. A chiral palladium(II) complex was thus obtained and its structure was confirmed by NMR spectroscopy and X-ray diffraction analysis.

Catalytic asymmetric Mannich-type reactions of fluorinated ketoesters with N-Boc aldimines in the presence of chiral palladium complexes

The catalytic enantioselective Mannich reaction promoted by chiral palladium complexes is described. The treatment of α-fluoro-β-ketoesters with N-Boc-aldimines under mild reaction conditions afforded the corresponding β-aminated α-fluoro-β-ketoesters with excellent enantioselectivities (up to 99% ee).

Diphenylprolinol-Derived Symmetrical and Unsymmetrical Chiral Pincer Palladium(II) and Nickel(II) Complexes: Synthesis via One-Pot Phosphorylation/Metalation Reaction and C−H Activation

The symmetrical P-stereogenic bis-phosphoramidite PCP pincer Pd(II) complexes 1 and 2 were easily prepared by a “four-component, one-pot phosphorylation/palladation” procedure via C−H bond activation of the related ligands. In this synthetic procedure, (S)-diphenyl(pyrrolidin-2-yl)methanol was first phosphonated with PCl3 to afford the expected phosphorochloridate adduct, which then reacted in situ with resorcinol or disubstituted resorcinol, followed by treatment with PdCl2. The first examples of the unsymmetrical P-stereogenic phosphoramidite- and imidazoline-containing PCN pincer Pd(II) complex 3 and Ni(II) complex 4 could be obtained in a similar manner by using a chiral imidazoline-containing m-phenol derivative instead of resorcinol as a backbone. 31P NMR of the complexes confirmed the formation of a single diastereoisomer concerning the P-stereogenic center, and its absolute configuration was determined by an X-ray crystal structure determination. Preliminary investigations on the use of these comp...

Metal Effects on the Asymmetric Synthesis of a New Heterobidentate As/P=S Ligand

AbstractThe cycloaddition reaction between 3,4‐dimethyl‐1‐phenylarsole and diphenylvinylphosphane sulfide was promoted by chiral palladium and platinum complexes containingortho‐metalated (S)‐[1‐(dimethylamino)ethyl]naphthalene. They exhibited similar stereoselectivity; the palladium cycloadducts could not be separated via column chromatography and fractional crystallization, however, the corresponding platinum complexes could be successfully converted into their enantiomerically pure counterpart. A formal arsanylidene elimination reaction was observed on the liberated free As/P=S bidentate ligand.

Isolation and Characterization of a Chiral η1-Allyl Palladium DIPPAM Complex: Application to the Enantioselective Pd-Catalyzed Allylic Alkylation

In the presence of [Cl(C3H5)Pd]2, diphenylphosphinoazomethinylate salt (DIPPAM) 1a forms an original chiral η1-allyl palladium complex, 2. Precatalyst 2/MgBr2 is an efficient catalyst for asymmetric allylic alkylation, giving good yields and ee’s in the reactions of rac-4-acetoxy-2-pentene or rac-3-acetoxy-1,3-diphenyl-1-propene and dimethyl malonate (respectively 77% and 96% yield; 66% and 96% ee). Preliminary mechanistic studies have highlighted the key role of the η1-coordination mode of the allyl fragment.

Chiral palladium complexes based on derivatives of benzylamine and 2α-hydroxypinan-3-one

Synthesized and characterized new chiral palladium complexes, some of which contain asymmetric donor nitrogen atom. Nitrogen-containing derivatives (+) - and (-)-2α-hydroxypinan-3-one- (1R,2R,5R)-3-(benzylimino)-2,6,6-trimethylbicy- clo[3.1.1]heptane-2-ol (HL1), (1S,2S,3S,5S)-3- (benzylamino)-2,6, 6-trimethylbicyclo[3.1.1]- heptane-2-ol (HL2), (1R,2R,5R)-3-((S)-α-methyl- benzylimino)-2,6,6-trimethylbicyclo[3.1.1]- heptane-2-ol (HL3), (1R,2R,3R,5R)-3-((S)-α-methyl- benzylamino)-2,6,6-trimethylbicyclo[3.1.1]- heptane-2-ol (HL4) -were studied as optically active ligands.

Synthesis of chiral β-aminoalcohol palladium complexes exhibiting cytotoxic properties

Original palladium complexes involving (-)-ephedrine, (-)-norephedrine, L-prolinol, L-valinol and L-isoleucinol have been rapidly prepared in neutral or basic medium and simply purified. They have been fully characterized by classical analytical methods and four of them were characterized by X-Ray analysis. In parallel with the experimental work, HF-DFT(B3LYP/PCM) computations were performed to obtain additional structural information. Their antiproliferative properties have been evaluated and some complexes showed small activities especially towards HT29 human cancer cells.

Asymmetric Synthesis of Functionalized 1,3-Diphosphines via Chiral Palladium Complex Promoted Hydrophosphination of Activated Olefins

Aldehyde, ester- and keto-functionalized monophosphine palladium complexes containing the ortho-metalated (R)-(1-(dimethylamino)ethyl)naphthalene as the chiral auxiliary and reaction promoter were synthesized via hydrophosphination of acrolein and the subsequent Wittig reactions in a one-pot process. Under very mild conditions, the second-stage hydrophosphination of the monophosphine substrates gave the corresponding ester-, keto-, and hydroxyl-functionalized chiral 1,3-bis(diphenylphosphino)propane palladium complexes with good yields and stereoselectivities. The coordination properties and absolute configurations of the novel 1,3-diphosphine complexes were established by single crystal X-ray crystallography. The enantiomerically pure functionalized diphosphine ligands with ester and keto functionalities could be subsequently liberated stereospecifically by treatment of the corresponding dichloro palladium complexes with aqueous potassium cyanide in high yields.

ChemInform Abstract: Enantioselective Fluorination of β‐Keto Phosphonates and β‐Ketoesters Catalyzed by Chiral Palladium Complexes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Palladium complexes with abnormal N-heterocyclic carbene ligands derived from 1,2,3-triazolium ions and their application in Suzuki coupling

Chiral and achiral pincer type palladium complexes bearing abnormal N-heterocyclic carbene ligands derived from 1,2,3-triazole are reported. Both complexes are effective as catalysts for non-asymmetric Suzuki coupling reaction for the synthesis of biphenyl derivatives. However, both the complexes failed to catalyze the formation of binaphthyl derivatives, by the asymmetric Suzuki coupling in case of the chiral complex and the non-asymmetric version in case of the achiral pincer complex. Instead deboronation of arylboronic acid occurred very efficiently leaving the aryl bromide intact.

Asymmetric Synthesis of Diphosphine Ligands Containing Phosphorus and Carbon Stereogenic Centers by Means of a Chiral Palladium Complex Promoted Hydrophosphination Reaction

An organopalladium complex containing ortho-metalated (R)-(1-(dimethylamino) ethyl)naphthalene as the chiral auxiliary has been used to promote the asymmetric hydrophosphination reaction between diphenylphosphine and phenyldi[(Z)-prop-1-enyl]phosphine in high regio- and stereoselectivity under mild conditions. The hydrophosphination reaction generated only two diastereomers in a ratio of 1:1. The two hydrophosphination products contained both phosphorus and carbon stereogenic centers and were subsequently isolated by fractional crystallization. Their absolute stereochemistries were analyzed by X-ray crystallography. The naphthylamine auxiliary could be removed chemoselectively from the template products by treatment with concentrated hydrochloric acid to form the corresponding optically pure neutral dichloro complexes. Subsequently, the dichloro complexes underwent ligand displacement with aqueous cyanide to generate the optically pure diphosphine ligands in high yields.