Dicationic Palladium Research Articles

Acid‐Free Intermolecular Hydroarylation of Acetylene Catalyzed by Dicationic Palladium(II) and Platinum(II) Ethylene Complexes

AbstractFour dicationic palladium and platinum ethylene complexes of the type [M(PNP)(C2H4)]X2 (M=Pd, Pt; X=BF4, SbF6, PNP=2,6‐bis(diphenylphosphinomethyl)pyridine) were studied as pre‐catalysts for the intermolecular hydroarylation of acetylene under acid‐free conditions. The palladium complex [Pd(PNP)(C2H4)](SbF6)2 was found to be the most active catalyst for the addition of pentamethylbenzene to acetylene at room temperature. In a 31P NMR spectroscopic study the impact of the counter anion on the rate determining step was demonstrated. Various reaction parameters were screened to optimize the catalytic efficiency. The presence of small amounts of water were beneficial and increased the reaction rate. Water acts as co‐catalyst assisting in proton transfer during the catalytic reaction. After optimization of the reaction conditions, a benchmark for the palladium(II) catalyzed hydroarylation of acetylene was achieved with TON 200 at room temperature in 24 h under acid‐free conditions. However, this catalytic system has a very limited substrate scope.

Electron-poor hemilabile dicationic palladium NHC complexes - synthesis, structure and catalytic activity.

We present a new class of dicationic palladium NHC complexes with two carbene ligands bearing different aryl substituents and a hemilabile pyrimidyl group. They can either be synthesized from the imidazolium salts via the silver transmetalation route to a halide-free palladium(ii) precursor or by direct deprotonation by palladium acetate. For four complexes we could determine their solid-state structures by X-ray diffraction experiments. Insight gained by NMR spectroscopy and DFT calculations revealed that in solution the two potentially bidentate ligands interchange between chelating and non-chelating coordination modes. The preference of these coordination modes is governed by the steric influence of the different ligands. The complexes were shown to be active catalysts for the hydroarylation of alkynes, and their performance was rationalized by DFT calculations.

Bi- and Multilayered Assembly of Amphiphilic Pd(II) and Pt(II) Complexes with N-Alkyl-4,4′-bipyridinium Ligands

Abstract Alternating transition metal-organic bi- and multilayers composed of dicationic (ethylenediamine)palladium(II) and platinum(II) complexes and N-alkyl-4,4′-bipyridinium, [(η3–C3H5)Pd{4,4′-bpy-N-(CH2)12OC6H3-3,5-(OMe)2}(OAc)]NO3 and [M{4,4′-bpy-N-(CH2)12OC6H3-3,5-(OMe)2}2(en)](NO3)4 (M = Pd, Pt, en = 1,2-ethylenediamine), were synthesized on mica surface by simple casting method from aqueous solution.

Novel Palladium(II) and Platinum(II) Complexes with a Fluoropiperazinyl Based Ligand Exhibiting High Cytotoxicity and Anticancer ActivityIn Vitro

cis-Dichloro-palladium(II) andcis-dichloro-platinum(II) complexes (2,4) of the general formula [M(N-N)Cl2] (M=Pd(II) and Pt(II), N-N= 1,2-diamino-4-fluoro-5-(4-methyl-1-piperazinyl) benzene, (DFMPB)) and the dicationic palladium(II) complex [Pd(N-N)(CH3CN)2](BF4)2(3) have been prepared and characterized by elemental analysis,1H-NMR-, mass spectroscopy, and IR spectroscopy. The cytotoxic effect of these complexes against MDA-231 and MCF-7 human breast cancer cell lines and K562 human leukemia cell line has been studied. The influence was dose dependent and varies with cell type. The palladium(II) complex (2) showed superior cytotoxic effect compared with the corresponding platinum(II) complex and the standard, cisplatin, when tested against all the above cell lines.

ジカチオン性パラジウム錯体を用いたフルオロアルキル化合物の触媒的不斉合成

ジカチオン性パラジウム錯体を用いたフルオロアルキル化合物の触媒的不斉合成

Anchoring sulfonic acid on silica surface through Si[sbnd]C bond for immobilization of catalyst for polyketone synthesis

Sulfonic acid groups were anchored on a silica surface through robust SiC bonds. The successive treatment of dehydroxylated silica with benzylmagnesium chloride and H2SO4 resulted in the surface tethering of CH2C6H4SO3H groups at a high coverage rate (0.50-CH2C6H4SO3H/nm2). The pore structure of the silica remained unchanged during this surface-modification process. Next, the CH2C6H4SO3H groups on the surface were successfully used for preparing a supported catalyst for CO/ethylene copolymerization; the ≡SiCH2C6H4SO3H groups on the surface were reacted with [1,3-bis(di(2-methoxyphenyl)phosphino)propane]Pd(OAc)2 to generate dicationic palladium species, which were anchored on the silica surface through ionic interactions with the sulfonate anions generated on the surface. The supported catalyst prepared in this way exhibited a high activity (up to 43kg/g-Pd or 0.61kg/g-cat) with respect to CO/ethylene copolymerization. The morphology of the obtained polymer particles replicated that of the silica particles. Thus, a polymer powder that exhibited a high bulk density (0.30g/mL) could be obtained while causing minimal reactor fouling.

Lewis Acid Catalyzed Asymmetric Three-Component Coupling Reaction: Facile Synthesis of α-Fluoromethylated Tertiary Alcohols.

A chiral dicationic palladium complex is found to be an efficient Lewis acid catalyst for the synthesis of α-fluoromethyl-substituted tertiary alcohols using a three-component coupling reaction. The reaction transforms three simple and readily available components (terminal alkyne, arene, and fluoromethylpyruvate) to valuable chiral organofluorine compounds. This strategy is completely atom-economical and results in perfect regioselectivities and high enantioselectivities of the corresponding tertiary allylic alcohols in good to excellent yields.

Catalytic Asymmetric Synthesis of Tertiary Alcohols and Oxetenes Bearing a Difluoromethyl Group.

The catalytic asymmetric ene reaction with difluoropyruvate as an electrophile in the presence of a dicationic palladium complex is shown. This is the reliable and practical catalytic asymmetric synthesis for various α-CF2H tertiary alcohols in high yields and enantioselectivities. The reaction with isobutene can be catalyzed efficiently under solvent-free conditions with low catalyst loading (up to S/C 2000). Furthermore, difluoropyruvate is applicable to the [2 + 2] cycloaddition reaction in high yields and enantioselectivities.

Chiral Pd-catalyzed trifluoropyruvate-ene reactions with steroidal side chains for late-stage fluoromethyl-functionalization: remarkably high agonist activities of ene products even in low VDR binding affinity

The highly enantioselective trifluoropyruvate-ene reactions of chiral steroid side chain olefins were achieved by dicationic palladium complexes as chiral Lewis acid catalysts to give steroidal ene-products in high diastereoselectivity. The ene products exhibited remarkably high agonist activities for human osteocalcin even in low vitamin D receptor binding affinity for human vitamin D hormone receptor.

ChemInform Abstract: Catalytic and Highly Enantioselective Friedel—Crafts Type Reactions of Heteroaromatic Compounds with Trifluoropyruvate and Glyoxylate by a Dicationic Palladium Complex.

AbstractThis asymmetric Friedel‐Crafts type reaction yields substituted furan, thiophene, and pyrrole derivatives with high enantioselectivity.

Catalytic and highly enantioselective Friedel–Crafts type reactions of heteroaromatic compounds with trifluoropyruvate and glyoxylate by a dicationic palladium complex

The highly enantioselective Friedel–Crafts alkylation of furan and thiophene derivatives with trifluoropyruvate, which have never provided the high level of asymmetric induction and yield until now, was achieved by using dicationic palladium complexes as Lewis acid catalysts. Moreover, glyoxylate instead of trifluoropyruvate as an electrophile led to complete change of regioselectivity with 2-trimethylsilylated furan, thiophene, and pyrrole derivatives to give the corresponding heteroarylated products in high yields and enantioselectivities. The respective products with trifluoropyruvate and glyoxylate could also be obtained via sequential catalytic reaction; intramolecular cyclization of alkynyldiols using cationic Au catalyst followed by Friedel–Crafts type reactions using dicationic Pd catalyst.

ChemInform Abstract: PdII‐Catalyzed Conjugate Addition of Boronic Acids to Ketoglutaconic Esters Toward the Synthesis of Functionalized Pyridazin‐3(2H)‐ones with Neuroprotective Activity.

AbstractThe dicationic palladium catalyst is found to be efficient for the regioselective conjugate addition of boronic acids to ketoglutaconic esters.

Aerobic oxidative Heck/dehydrogenation reactions of cyclohexenones: efficient access to meta-substituted phenols.

Jockeying for the (meta)position: A new dicationic palladium(II) catalyst, employing a 6,6′-dimethyl-2,2′-bipyridine ligand, promotes both the aerobic oxidative Heck coupling and dehydrogenation reactions of cyclohexenones. These reactions may be combined in a one-pot sequence to enable the straightforward synthesis of meta-substituted phenols (see scheme). As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Fluxional interconversion of divalent palladium complexes having NSNSN ligands between flexible SNS and rigid NNN-coordinated structures

Mono- and dicationic divalent palladium complexes having 2,6-bis(N-heteroarylsulfanylmethyl)pyridine ligands (NSNSN ligands) were synthesized and characterized. The NSNSN ligands were fixed in a rac-SNS tridentate coordination mode in the solid state, while the equilibria among meso-SNS, rac-SNS, and NNN isomers were observed in solution. The equilibrium between the SNS and NNN isomers could be modulated by temperature, as well as by the steric and electronic factors of the NSNSN and monodentate ligands. Lowering the temperature tended to make NNN isomers more predominant compared with SNS isomers. On the other hand, the steric demand between the ligands in the complexes shifted the equilibrium from NNN to SNS isomers. Introduction of pyridyl groups instead of pyrimidyl groups as N-heteroarenes also shifted the equilibrium to SNS isomers. DFT calculation indicated rapid ring inversion of the metallacycle moieties and relatively slow S-inversion in the SNS isomers, a result that was in good agreement with the experimentally observed dynamic behaviors. Both the experimental and theoretical results revealed that the SNS isomers had flexible structures in solution, whereas the NNN isomers were rigid and less dynamic. The mechanistic pathways for interconversion between SNS and NNN isomers were also calculated. Such calculations indicated that a pathway featuring a relatively unstable, distorted ax-SNN intermediate was plausible. The intermediate had an N-heteroarene on the coordinated sulfur atom at an axial position.

ChemInform Abstract: Catalytic Enantioselective Chlorination of Cyclic β‐Keto Esters in the Presence of Chiral Pd(II) Complexes.

AbstractAn efficient enantioselective electrophilic α‐chlorination of various cyclic β‐keto esters in the presence of a dicationic palladium complex is developed.

Preparation of dicationic palladium catalysts for asymmetric catalytic reactions

The synthesis of Pd(OTf)(2)·2H(2)O is described. This was used to generate two different types of chiral dicationic palladium complexes for highly enantioselective addition of aromatic amines to α, β-unsaturated conjugate alkenes ([(R-BINAP)Pd(OH(2))(2)][OTf](2) and [(R-BINAP)Pd(μ-OH)](2)[OTf](2)). The resulting optically active N-arylated β-amino acid derivatives are valuable synthetic intermediates for the synthesis of biologically active molecules and peptidomimetics. The reaction of (2E)-but-2-enoylcarbamate and aniline is shown as an example of the use of these catalysts for enantioselective aza-Michael addition. For the preparation of palladium(II) triflate, the time scale is 20 h 50 min, plus 5 h 15 min for the monomeric complex and plus 6 h 45 min for the dimeric complex.

ChemInform Abstract: Highly Enantioselective Friedel—Crafts Alkylation of Indole and Pyrrole with β,γ‐Unsaturated α‐Ketoester Catalyzed by Chiral Dicationic Palladium Complex.

AbstractThe reaction is efficiently catalyzed by sterically demanding complexes (I).

Simple Silver Salts and Palladium Bis(N-heterocyclic carbene) Complexes As Complementary Catalysts for the Nazarov Cyclization

Simple silver salts and dicationic palladium bis(N-heterocyclic carbene) complexes were found to be effective and complementary catalysts for Nazarov cyclizations of divinyl β-keto esters. A sterically hindered palladium bis(NHC) catalyst provided remarkable endo:exo selectivity in cyclizations of cyclohexenyl β-keto esters, whereas AgSbF6 gave improved yields with electron-deficient substrates. The high activities observed with silver salts are significant, given their widespread use as additives in catalytic Nazarov reactions.

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.

Dicationic Palladium(II) Complexes as Active Lewis Acid Catalysts for Polarized Nazarov Cyclization

Two new bidentate phosphonamidite ligands − 1,2-bis((3αS)-3,3-diphenyltetrahydro-2-oxa-6α-aza-1-phosphapentaleno)ethane, L1, and 1,2-bis((3αS)-3,3-diphenyltetrahydro-2-oxa-6α-aza-1-phosphapentaleno)benzene, L2 − were prepared from (S)-α,α-diphenylprolinol and either 1,2-bis(dichlorophosphino)ethane or 1,2-bis(dichlorophosphino)benzene, respectively. Reactions of L1 and L2 with one equivalent of Pd(PhCN)2Cl2 in dichloromethane result in the formation of the neutral complexes Pd(L1-P,P)Cl2, 2, and Pd(L2-P,P)Cl2, 3, in good yields (85% and 92%, respectively). Complexes 2 and 3 were fully characterized by NMR spectroscopy, elemental analyses, and X-ray crystallography. Chloride abstraction from 1 and 2 using two equivalents of AgSbF6 in the presence of excess diethylisopropylidene malonate (DIM) leads to the formation of the respective dicationic palladium complexes [Pd(L1-P,P)(DIM)][SbF6]2, 4, and [Pd(L2-P,P)(DIM)][SbF6]2, 5. As a result of the cationic nature of 4 and 5 and the labile coordination of DIM, t...