Η3-allyl Palladium Complexes Research Articles

Synthesis, Characterization and Photophysical Properties of Mixed Ligand (η3-Allyl)palladium(II) Complexes with N,N’Aromatic Diimines

Palladium(II) complexes of the general formula [Pd(η3-C3H5)(L)](PF6), where L is 4,7-diphenyl-1,10-phenanthroline (1), 2,9-dimethyl-1,10-phenanthroline (2), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (3), 5-methyl-1,10-phenanthroline (4), 3,4,7,8-tetramethyl-1,10-phenanthroline (5), and 2-(2′-pyridyl) quinoxaline (6), were synthesized and characterized using high-resolution ESI-MS, NMR techniques and, in the case of (6), single-crystal X-ray diffraction methods. In addition, their photophysical properties were investigated. Complexes (1)–(6) were emitted in the greenish-blue region, with those containing methyl-substituted phenanthrolines having the higher quantum yield (≈14%) in the solid state.

η3-allyl-Pd(II) complexes of 2-, 3- and 4-pyridylmethyl-coumarin esters

A series of 2-, 3- and 4-pyridylmethyl-coumarin esters ligands (1–3) and their η3-allyl palladium complexes (1-Pd–3-Pd) have been designed, synthetized, and characterized. NMR analysis of compounds 1-Pd–3-Pd indicated the presence of the allyl fragment. The molecular structures of 2, 3 and 1-Pd were determined by X-ray crystallographic analysis. The molecular structure of 1-Pd reveals that coumarin ligand (2) is coordinated to the palladium center via a monodentate fashion through the nitrogen atom of the pyridinyl fragment while, the allyl group is binding via a η3 fashion in an overall square-planar geometry completed with a chloride atom. The crystal packing is stabilized by a variety of weak intermolecular conventional and non-conventional interactions involving C–H–O/N hydrogen bonds, π–π and C–H–π interactions, which have been analyzed by Hirshfeld surface and non-covalent interactions analysis. The intermolecular interaction energies were explored using an energy framework analysis, which revealed that π–π and C–H–π interactions serve as the primary building blocks in these crystal packing.Graphical abstract

Palladium-catalyzed Dehydrogenative [3+3] Aromatization of Propyl Ketones and Allyl Carbonates

Abstract A Pd-catalyzed dehydrogenative [3+3] aromatization of 3-phenylpropyl ketones and allyl carbonates has been developed. The reaction gives various di- or tri-substituted aromatic ketones. The reaction consisting of five steps efficiently proceeded in a one-batch, one-manipulation setup. The postulated active species, η3-allyl palladium complex, works as a catalyst for triple dehydrogenations and mono allylation with high substrate controls.

Synthesis and Structural Study of Η3-Allyl Palladium(Ii) Complexes Supported by Coumarin Decorated with a Methyl-Pyridine Group Ligand

Synthesis and Structural Study of Η3-Allyl Palladium(Ii) Complexes Supported by Coumarin Decorated with a Methyl-Pyridine Group Ligand

Η3-Allyl Palladium Complexes Supported by Coumarin Decorated with a Methyl-Pyridine Group Ligands

Η3-Allyl Palladium Complexes Supported by Coumarin Decorated with a Methyl-Pyridine Group Ligands

Synthesis and comparative study of the anticancer activity of η3-allyl palladium(II) complexes bearing N-heterocyclic carbenes as ancillary ligands

In this paper we report the synthesis and characterization (NMR, IR, elemental analysis and XRD) of fifteen new Pd(II) allyl complexes containing at least one N-heterocyclic carbene ligand.The synthesized compounds and others previously published by our research group, have been tested against the six tumor lines OVCAR5, A2780, A2780cis (ovarian cancer), DLD1 (colon cancer), A549 (lung cancer) and A375 (malignant melanoma).This comparative study, involving also complexes coordinating NS and NP heteroditopic ligands, shows that most of the tested compounds exhibit a much powerful antitumor activity than cisplatin on all tumor cell lines examined.In many cases, the antiproliferative activity on the A2780 (cisplatin-sensitive) and A2780cis (cisplatin-resistant) lines is comparable, suggesting a different mechanism of action of this class of molecules as compared to cisplatin and its derivatives.Moreover, a selected number of compounds among those reported are particularly promising since exhibit a markedly lower activity toward normal cells than to cancer cells.

Activity and selectivity of carbon supported palladium catalysts prepared from bis(η3-allyl)palladium complexes in phenylacetylene hydrogenation

Liquid phase hydrogenation of phenylacetylene was investigated on a series of 9.1 wt% Pd/C catalysts prepared from bis(η3-allyl)palladium complexes, as well as commercial Russian Pd/C catalyst (GIPKH-108). Pd/C catalysts were characterized by oxygen absorption and SEM. All prepared Pd/C catalysts demonstrated very high selectivity to styrene. The reduction temperature of palladium precursor has a significant effect on the palladium dispersity, but the substituent near terminal carbon atom of allyl ligand affects the dispersity more essentially than reduction temperature. Pd/C catalyst prepared from bis[(η3-allyl)palladium acetate] showed highest metal dispersity, activity and selectivity in the hydrogenation of phenylacetylene to styrene.

D3h -Symmetric Porphyrin-Based Rigid Macrocyclic Ligands for Multicofacial Multinuclear Complexes in a One-Nanometer-Sized Cavity.

The one-step synthesis of D3h -symmetric cyclic porphyrin trimers 1 composed of three 2,2'-[4,4'-bis(methoxycarbonyl)]bipyridyl moieties and three porphyrinatozinc moieties was achieved from a nickel-mediated reductive coupling of meso-5,15-bis(6-chloro-4-methoxycarbonylpyrid-2-yl)porphyrinatozinc. Although cyclic trimers 1 were obtained as a mixture that included other cyclic and acyclic porphyrin oligomers, an extremely specific separation was observed only for cyclic trimers 1 when using columns of silica gel modified with pyrenylethyl, cyanopropyl, and other groups. Structural analysis of cyclic trimers 1 was carried out by means of NMR spectroscopy and X-ray crystallography. Treatment of an η(3) -allylpalladium complex with a cyclic trimer gave a tris(palladium) complex containing three η(3) -allylpalladium groups inside the space, which indicated that the bipyridyl moieties inside the ring could work as bidentate metalloligands.

Mechanistic Investigation of the Palladium-Catalyzed Synthesis of Allylic Silanes and Boronates from Allylic Alcohols

The mechanism of the palladium-catalyzed synthesis of allylic silanes and boronates from allylic alcohols was investigated. (1)H, (29)Si, (19)F, and (11)B NMR spectroscopy was used to reveal key intermediates and byproducts of the silylation reaction. The tetrafluoroborate counterion of the palladium catalyst is proposed to play an important role in both catalyst activation as well as the transmetalation step. We propose that BF(3) is generated in both processes and is responsible for the activation of the substrate hydroxyl group. An (η(3)-allyl)palladium complex has been identified as the catalyst resting state, and the formation of (η(3)-allyl)palladium complexes directly from allylic alcohols has been studied. Kinetic analysis provides evidence that the turnover limiting step is the transmetalation, and insights into notable similarities between the borylation and the silylation reaction mechanisms enabled us to considerably improve the stereoselectivity of the borylation.

Synthesis, characterization and low temperature self assembling of (η3-allyl)palladium complexes with 2-pyridyl-1,2,3-triazole bidentate ligands. Study of the catalytic activity in Suzuki–Miyaura reaction

The cationic complexes [Pd(η3-C3H5)(2-((4-propyl-1H-1,2,3-triazol-1-yl)methyl)pyridine)](X) (2: X = BF4−, 3: X = ClO4−), and [Pd(η3-2-CH3-C3H4)(2-((4-propyl-1H-1,2,3-triazol-1-yl)methyl)-pyridine)](BF4−) (4) have been synthesized by reacting the appropriate palladium-allyl precursor with 2-((4-propyl-1H-1,2,3-triazol-1-yl)methyl)pyridine in the presence of AgBF4 or AgClO4. The solid-state structure of 2 has been determined by single-crystal X-ray diffraction analysis. According to 1H NMR spectroscopy the allyl protons undergo syn–syn, anti–anti exchange. 1H NMR spectroscopy reveals that in acetone at temperatures lower than 223 K these complexes form aggregates the stability of which is attributed to solvophobic interactions. Complex 2 is an active catalyst for the S–M coupling of aryl bromides with phenylboronic acid; good reaction rates are obtained only with activated substrates, whereas with deactivated substrates catalyst decomposition to palladium black occurs.

Synthesis and Characterization of η3-Allyl Palladium(II) Complexes with Tetraalkyldiphosphine Disulfides, R2P(S)P(S)R2 (R=Me, Et, nPr, nBu, Ph)

New allyl-palladium tetraalkyl(phenyl)diphosphine disulfide complexes, [(η3-CH2CMeCH2)Pd(tmps)]Cl, [(η3-CH2CMeCH2) Pd(teps)]Cl, [(η3-CH2CMeCH2)Pd(tpps)]Cl, [(η3-CH2CMeCH2) Pd(tbps)]Cl, [(η3-CH2CMeCH2)Pd(tPhps)]Cl, and [(R2P(S)P(S) R2) R=Me, (tmps); Et, (teps); nPr, (tpps); nBu, (tbps); Ph, (tPhps)] have been prepared from the addition of tetraalkyl (phenyl)diphosphine disulfide to [(η3-CH2CMeCH2)Pd(μ-Cl)]2. All the complexes have been characterized by elemental analysis, Fourier-transform infrared (FT-IR), nuclear magnetic resonance (1H-NMR and 31P-{1H}-NMR) spectroscopy, and fast atom bombardment (FAB) mass spectrometry. The spectroscopic studies suggest that ligands are cis-chelate bidentate coordination, forming five-membered Pd-S=P-P=S palladacycles, with the η3-allyl group completing the coordination sphere.

ChemInform Abstract: Palladium-Complex-Catalyzed Cyanation of Allylic Carbonates and Acetates Using Trimethylsilyl Cyanide.

Allylic carbonates are cyanated in high yields to β,γ-unsaturated carbonitriles using trimethylsilyl cyanide in the presence of a catalytic amount (5 mol %) of Pd(PPh3)4 in THF under reflux. In the reaction, cinnnamyl methyl carbonate affords cinnamyl cyanide in 98% yield. Allylic acetates also provide the corresponding carbonitriles, but often in lower yields. The cyanations of several cis- and trans-alicyclic substrates proceed cleanly (stereoselectivity > 99%) with overall retention. Characterization and reaction of palladium complexes relevant to the present catalysis indicate that transmetalation of an η3-allyl palladium complex with trimethylsilyl cyanide is facile, while the resulting cyano(η3-allyl)palladium complexes afford the corresponding allylic cyanides only when excess trimethylsilyl cyanide is present. Stereochemistry of the product indicates that the CN attacks the η3-allyl moieties from the palladium side.

Effects of substituents in the cationic and anionic η3-allylpalladium complexes according to data from 13C NMR spectroscopy and quantum chemical calculations

A linear correlation of chemical shifts (δ) of signals in the 13C NMR spectra of the unsubstituted terminal carbon atom of the allyl ligand in [(1-R-η3-C3H4)Pd]NO3 (R = Me, CH2OMe, CO2Me, COMe, CHO) with the substituent constants σ+ and σs- in acetone solutions was found. A considerable deviation from linearity was observed for R = Ph. The 13C nuclear magnetic screening constants were calculated by the DFT method in the GIAO approximation for equilibrium geometries of the cations [(1-R-η3-C3H4)Pd(Me2C=0)2]+ and anions [(1-R-η3-C3H4)PdCl2]s-. In the latter case, the theoretical and experimental δ values are consistent. The influence of the substituent R on the geometric parameters and charges on atoms in the neutral, anionic, and cationic η3-allylpalladium complexes is discussed.

Preparation, coordination and catalytic use of planar-chiral monocarboxylated dppf analogues

A novel polar dppf derivative possessing only planar chirality, 1′,2-bis(diphenylphosphino)-ferrocene-1-carboxylic acid (Hdpc), has been synthesised in racemic form and resolved into enantiomers via esters with D-glucose diacetonide ((Rp)- and (Sp)-3). (Rp)-Hdpc was further converted to a series of N-substituted amides that were studied as ligands for Pd-catalysed enantioselective allylic alkylation of racemic (E)-1,3-diphenylprop-2-en-1-yl acetate or ethyl carbonate with malonate esters, showing high activity and good enantioselectivity (er up to 10 : 90). The catalytic results were correlated with the structural data (X-ray diffraction and solution NMR) for (η3-allyl)palladium(II) complex (Rp)-[Pd(η3-1,3-Ph2C3H3){Fe(η5-C5H3-1-(C(O)NHCH2Ph)-2-(PPh2-κP))(η5-C5H4PPh2-κP)}]ClO4 (16) as a model of the plausible reaction intermediate. A further study into the coordination properties of Hdpc led to isolation of chelate complex [PdCl2(Hdpc-κ2P,P′)] (12). The crystal structures of rac-Hdpc, methyl ester of (Rp)-Hdpc, glycoside (Rp)-3, and 12·Me2CO suggested a close structural relationship between dppf and Hdpc.

New Picropodophyllin Analogs via Palladium-Catalyzed Allylic Alkylation−Hiyama Cross-Coupling Sequences

Unsaturated malonyl esters underwent Pd-catalyzed intramolecular allylic alkylation to give 4-vinyl-substituted gamma-lactones. In contrast to the formerly studied cyclization of malonamides, this reaction could be achieved only with a substrate incorporating a suitably positioned silicon moiety, which directs the ionization toward the desired eta(3)-allylpalladium complex. The resulting 4-[dimethyl-(2-thienyl)silylvinyl]lactone could be subsequently engaged into Hiyama couplings with various iodoarenes, to give the corresponding 4-(alpha-styryl)-gamma-lactones. The use of a specifically substituted iodoarene generated an advanced tetracyclic lactone intermediate incorporating rings A-D of lignans belonging to the podophyllotoxin family. Subsequent electrophilic aromatic substitution with a variety of electron-rich arenes afforded the target picropodophyllin analogs.

Enantioselecitve Elimination of Pd–H from η3-Allylpalladium–Tol BINAP Complexes. Evidence of Syn Elimination Pathway

Abstract The palladium-catalyzed elimination of the bicyclic cis-acetate 1b using Pd catalyst and (R)-p-Tol BINAP gave the (S)-diene 2 with 58% ee. Bicyclic η3-allylpalladium complex 3a with (R)-p-Tol BINAP, considered as an intermediate in the catalytic reaction from 1b, was prepared. Enantioselectivity in decomposition of 3a is dependent on the reaction conditions. The thermal decomposition of 3a without base gave the (S)-2 with 70% ee. However, the decomposition of 3a in the presence of excess base gave (R)-2 with 58% ee. Syn elimination from 3a was found to proceed preferentially from the decomposition results of the deuterium-labeled complexes.

Preparation of Chiral Phosphinoferrocene Carboxamide Ligands and Their Application to Palladium-Catalyzed Asymmetric Allylic Alkylation

A series of phosphinoferrocene carboxamides bearing achiral (benzyl) and chiral [(R)- and (S)-1-phenylethyl] substituents at the amide nitrogen have been prepared from 1‘-(diphenylphosphino)ferrocenecarboxylic (Hdpf) and (Sp)-2-(diphenylphosphino)ferrocenecarboxylic ((Sp)-1) acids and tested as ligands for enantioselective allylic alkylation of 1,3-diphenylallyl acetate with dimethyl malonate. At room temperature, the alkylation reactions proceeded with complete conversions and ee's up to 90%, the most efficient being the planar-only chiral ligand (Sp)-2-(diphenylphosphino)-1-(N-benzylcarbamoyl)ferrocene ((Sp)-2). The crystal structures of (Sp)-2 and the cationic (η3-allyl)palladium(II) complex [Pd(η3-1,3-Ph2C3H3){(Sp)-2-κ2O,P}]ClO4 ((Sp)-8) have been determined by single-crystal X-ray diffraction and solution NMR data were obtained to provide an insight into the mechanism of chiral discrimination.

Relative Rates for the Amination of η3-Allyl and η3-Benzyl Complexes of Palladium

Reactions of nucleophiles with metal-bound hydrocarbyl pi-ligands bound in an eta3-fashion are key steps in a variety of carbon-carbon and carbon-heteroatom bond-forming reactions. To reveal factors that control the rates of reaction of nucleophiles with this type of ligand, the rates of reactions of an aromatic and an aliphatic amine with a series of eta3-allyl, eta3-benzyl, and eta3-phenethyl palladium complexes ligated by the bisphosphine (R)-BINAP to form allylic and benzylic amines were measured. These data showed that the less common addition to an eta3-benzyl complex is faster than the more common addition to an eta3-allyl complex. The relative rates of reaction followed the trend naphthylmethyl > naphthylethyl > benzyl > 1,1-dimethylallyl > allyl. Computational studies suggest that there is a correlation between the amount of positive charge at the site of nucleophilic attack and the rate of C-N bond formation.

Allyl(Acetylacetonato)Palladium (II) Complexes: Versatile Precursors for the Synthesis of Dimeric Allylpalladium (II) Complexes

The facile synthesis and characterisation of several new dimeric (η3-allyl)palladium (II) complexes of the type, [Pd(μ-L)2(η3-C3H4R)2] [R = H or Me; LH = 4-CH3C6H4SH; 3,5-R'2pzH (R’ = But or Ph]; ArNNNHAr (Ar = 4-FC6H4); PhNC(Ph)NHPh] are reported.

Synthesis and characterization of η3-allyl palladium(II) complexes, [(η3-allyl)Pd(S2X)] (X = CNMe2, CNEt2, COEt, PPh2)

The complexes [(η3-C6H9)Pd(η2-S2CNR2)] (R = Me, 1; Et, 2), [(η3-Me2CCMeCH2)Pd (η2-S2COEt)] 3 and [(η3-Me2CCMeCH2)Pd(η2-S2PPh2)] 4 have been synthesized by reaction of [(η3-allyl)Pd(μ-Cl)]2 with NaS2CNR2 (R = Me, Et), KS2COEt and NaS2PPh2. They have been characterized by elemental analysis, FTIR, 1H NMR and FAB mass spectrometry. Spectroscopic studies suggest that sulfur donor ligands are bidentate, forming Pd–S–C–S and Pd–S–P–S palladacycles, an η3-allyl group completing the coordination sphere.