Carbonyl allylation of aldehydes and ketones with allylic chlorides catalyzed by immobilization of palladium in MCM-41

The heterogeneous carbonyl allylation of aldehydes and ketones with allylic chlorides was achieved in DMF using SnCl₂ as reducing agent at 25-40 °C in the presence of a 3-(2-aminoethylamino)propyl-functionalized MCM-41-immobilized palladium(II) complex [MCM-41-2N-Pd(II)], yielding a variety of homoallylic alcohols in good to high yields. This heterogeneous palladium catalyst exhibited higher activity than (N-propylethylenediamine)PdCl₂ and can be recovered and recycled by a simple filtration of the reaction solution and used for at least 5 consecutive trials without any decreases in activity.     

MCM-41-supported bidentate phosphine palladium(0) complex as an efficient catalyst for the heterogeneous Stille reaction

A Stille coupling reaction of organostannanes with organic halides has been developed in the presence of a catalytic amount of MCM-41-supported bidentate phosphine palladium(0) complex (0.5 mol %) in DMF/H₂O (9:1) under air atmosphere in high yields. This polymeric palladium catalyst exhibits higher activity than Pd(PPh₃)₄ and can be reused at least 10 times without any decrease in activity.     

N-alkylpyridinium quaternization combined with liquid chromatography–electrospray ionization-tandem mass spectrometry: A highly sensitive method to quantify fatty alcohols in thyroid tissues

A highly sensitive method was developed for the identification and quantification of fatty alcohols in biological tissues. In the presence of pyridine-d₀ and triflic anhydride (Tf₂O), fatty alcohols were converted into permanently charged N-alkylpyridinium ions. Stable isotope-labeled derivatives were generated by pyridine-d₅ and added as internal standard (IS). The mixture was analyzed by liquid chromatography coupled to positive electrospray ionization tandem mass spectrometry (LC–ESI-MS/MS). This method was optimized and validated in terms of reaction time, derivatization efficiency, stability, desalting, and ion suppression effect. Besides, fatty alcohols exhibited good linear relationship (r² > 0.993) over the concentration range of 10 ng mL⁻¹–1 μg mL⁻¹. The limits of detection (LODs) were lowered from previously reported 0.1 ng mL⁻¹ to 0.25 pg mL⁻¹. Precision (RSD% < 15.6%), accuracy (93.0–107.2%), matrix effect, and recovery (in thyroid tissues) were validated as well. Finally, this method was applied for the analysis of ten even carbon-numbered fatty alcohols (C₈–C₂₄) in human thyroid carcinoma and para-carcinoma tissues, revealing a significant decrease of fatty alcohols (free and esterified) in thyroid carcinoma tissues (p < 0.05).     

Propylene oxidation by palladium nitro and nitrato complexes: in situ NMR and IR studies

The mechanism of the propylene oxidation by Pd(NO_n)Cl_2 − m(CH₃CN)₂ complexes (n = 2, 3; m = 0, 1, 2) in chloroform solutions has been studied by ¹H NMR and IR spectroscopy. The main reaction products are acetone and 2-nitropropylene, with their ratio depending on the equilibrium existing in the reaction solutions between palladium complexes containing NO_n ligands bonded to a palladium atom via either an oxygen or a nitrogen atom. Reactivities of the oxygen bonded nitrato and nitrito complexes are significantly higher than that of the nitrogen bonded nitro complex. Various new organopalladium intermediates have been observed and monitored in situ. A reversible insertion of the coordinated propylene into the Pd-O or Pd-N bonds results in nitrato-, nitrito- and nitropalladation intermediates, which then decompose via a β-hydrogen elimination. Two isomers of the nitritopalladation intermediate have been detected, i.e., a palladium metallacycle and an open ring complex, with the latter being much more reactive towards the β-hydrogen elimination than the former. The decomposition of the nitrato- and nitritopalladation intermediates results in the organometallic precursor of acetone, i.e., an acetonylpalladium complex, and then in acetone itself. On the other hand, the nitropalladation intermediate originates 2-nitropropylene. In the presence of dioxygen, which re-oxidizes the nitrosyl groups, the acetone formation becomes a catalytic reaction with respect to both palladium and nitrogen.     

Determination of palladium in various samples by atomic absorption spectrometry after preconcentration with dimethylglyoxime on silica gel

A preconcentration method based on the adsorption of palladium-dimethylglyoxime (DMG) complex on silica gel for the determination of palladium at trace levels by atomic absorption spectrometry (AAS) has been developed. The retained palladium as Pd(DMG)₂ complex was eluted with 1 mol l⁻¹ HCl in acetone. The effect of some analytical parameters such as pH, amount of reagent and the sample volume on the recovery of palladium was examined in synthetic solutions containing street dust matrix. The influence of some matrix ions on the recovery of palladium was investigated by using the developed method when the elements were present both individually and together. The results showed that 2500 μg ml⁻¹ Na⁺, K⁺, Mg²⁺, Al³⁺ and Fe³⁺; 5000 μg ml⁻¹ Ca²⁺ ; 500 μg ml⁻¹ Pb²⁺; 125 μg ml⁻¹ Zn²⁺; 50 μg ml⁻¹ Cu²⁺ and 25 μg ml⁻¹ Ni²⁺ did not interfere with the palladium signal. At the optimum conditions determined experimentally, the recovery for palladium was found to be 95.3±1.2% at the 95% confidence level. The relative standard deviation and limit of detection (3s/b) of the method were found to be 1.7% and 1.2 μg l⁻¹, respectively. In order to determine the adsorption behaviour of silica gel, the adsorption isotherm of palladium was studied and the binding equilibrium constant and adsorption capacity were calculated to be 0.38 l mg⁻¹ and 4.06 mg g⁻¹, respectively. The determination of palladium in various samples was performed by using both flame AAS and graphite furnace AAS. The proposed method was successfully applied for the determination of palladium in the street dust, anode slime, rock and catalytic converter samples.     

Iridium-catalyzed oxidative esterification reaction of aliphatic aldehydes and olefinic alcohols with precoordination of the double bond of alcohols to iridium

A novel iridium-catalyzed oxidative esterification reaction of aliphatic aldehydes and olefinic alcohols in toluene was found under mild conditions of [IrCl(cod)]₂ (5 mol %) in combination with K₂CO₃ (10 mol %) at rt.     

Dicationic ((−)-sparteine)palladium-catalyzed enantioselective aldol reaction of aldehydes with 1-phenyl-1-trimethylsilyloxyethene, proceeding via a palladium enolate

A dicationic ((−)-sparteine)palladium complex underwent a superior catalytic enantioselective aldol reaction of aldehydes with 1-phenyl-1-trimethylsilyloxyethene performing satisfactorily, starting with ((−)-sparteine)PdCl₂ and AgSbF₆ as catalyst precursors (1 mol % loading) in the presence of 3 Å molecular sieves over the reaction.     

Rhodium-catalyzed carbonyl allylations by allylic alcohols with tin(II) chloride

Rhodium complexes such as [RhCl(cod)]₂, [Rh(cod)₂]BF₄, and [Rh(cod)(CH₃CN)₂]BF₄ function as catalysts for carbonyl allylations by allylic alcohols with 1 equimolar amount of tin(II) chloride to each allylic alcohol and aldehyde in THF at 50 °C to produce the corresponding homoallylic alcohols.     

Synthesis and polymerization of novel fluorinated acrylates and methacrylates bearing alkoxyl groups derived from radical addition reaction of perfluoroisopropenyl ester

Radical addition of 2-benzoxypentafluoropropene [CF₂C(CF₃)OCOC₆H₅] (BPFP) with alcohols such as ethanol and 2-propanol was investigated to afford fluorinated alcohols. Radical addition of BPFP with cyclic ethers such as tetrahydrofuran, 1,3-dioxolane and tetrahydropyran was also achieved to afford addition products followed by hydrolysis to yield fluorinated alcohols possessing cyclic structures. Novel fluoroalkyl acrylates and methacrylates were synthesized from the fluorinated alcohols with (meth)acryloyl chlorides. Radical polymerization of the fluoroalkyl (meth)acrylates yielded polymers of 1.2 × 10⁵ as the highest molecular weight.     

Steric and electronic effects in stabilizing allyl-palladium complexes of “P-N-P” ligands, X2PN(Me)PX2 (X = OC6H5 or OC6H3Me2-2,6)

The chemistry of η³-allyl palladium complexes of the diphosphazane ligands, X₂PN(Me)PX₂ [X = OC₆H₅ (1) or OC₆H₃Me₂-2,6 (2)] has been investigated.The reactions of the phenoxy derivative, (PhO)₂PN(Me)P(OPh)₂ with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = H or Me; R′ = H, R″ = Me) give exclusively the palladium dimer, [Pd₂{μ-(PhO)₂PN(Me)P(OPh)₂}₂Cl₂] (3); however, the analogous reaction with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = Ph) gives the palladium dimer and the allyl palladium complex [Pd(η³-1,3-R′,R″-C₃H₃)(1)](PF₆) (R′ = R″ = Ph) (4). On the other hand, the 2,6-dimethylphenoxy substituted derivative 2 reacts with (allyl) palladium chloro dimers to give stable allyl palladium complexes, [Pd(η³-1,3-R′,R″-C₃H₃)(2)](PF₆) [R′ = R″ = H (5), Me (7) or Ph (8); R′ = H, R″ = Me (6)].Detailed NMR studies reveal that the complexes 6 and 7 exist as a mixture of isomers in solution; the relatively less favourable isomer, anti-[Pd(η³-1-Me-C₃H₄)(2)](PF₆) (6b) and syn/anti-[Pd(η³-1,3-Me₂-C₃H₃)(2)](PF₆) (7b) are present to the extent of 25% and 40%, respectively. This result can be explained on the basis of the steric congestion around the donor phosphorus atoms in 2. The structures of four complexes (4, 5, 7a and 8) have been determined by X-ray crystallography; only one isomer is observed in the solid state in each case.     

An efficient protocol for copper-free palladium-catalyzed Sonogashira cross-coupling in aqueous media at low temperatures

A thorough study on copper-free Sonogashira cross-couplings in water was carried out using the palladacycle, [{Pd(μ-Cl){κ²-P,C-P(ⁱPr)₂(OC₆H₃-2-Ph)}}₂] as pre-catalyst with different bases and palladium concentrations. The highly active pre-catalyst imparts good to near quantitative yields using a concentration of 0.25 mol % at 40 °C. This broadly applicable protocol exhibits high tolerance of functional groups and substitution patterns.     

Pyridinium chlorochromate catalyzed oxidation of alcohols to aldehydes and ketones with periodic acid

A facile pyridinium chlorochromate (PCC) catalyzed (2 mol %) oxidation of alcohols to ketones and aldehydes using 1.05 equiv of H₅IO₆ in acetonitrile is described here.     

A convenient procedure for palladium catalyzed cyanation using a unique bidentate phosphorus ligand

A palladium complex bearing 1,2-diphenyl-3,4-diphosphinidenecyclobutene ligand (DPCB) has been used to facilitate the catalytic cyanation of aryl bromides. A series of substituted benzonitriles was prepared in good to high yields by the treatment of the corresponding aryl bromides with Zn(CN)₂ in N-methyl-2-pyrrolidone in the presence of 2-4 mol % catalyst at 100 °C for 16 h.     

Palladium-catalyzed oxidation of cyclohexanones to conjugated enones using molecular oxygen

Oxidation of cyclohexanones into conjugated enones with molecular oxygen as oxidant was achieved by palladium catalysts. A catalyst system consists of 1 mol % Pd(OCOCF₃)₂ and 5,5′-dimethyl-2,2′-bipyridine accomplished maximum 84% yield for the oxidation of cyclohexanone and 51-78% yields for 4-substituted-cyclohexanones.     

Palladium-benzimidazolium salt catalyst systems for Suzuki coupling: development of a practical and highly active palladium catalyst system for coupling of aromatic halides with arylboronic acids

Palladium-benzimidazolium salt catalyst systems have been studied for the Suzuki coupling. A different substitutent effect has been uncovered with respect to nitrogen substituents in the benzimidazolium salts from the palladium-imidazolium salt analogs. A practical and highly active palladium catalyst system, PdCl₂/N,N′-dibenzylbenzimidazolium chloride 2, has been identified for the Suzuki coupling of aromatic halides with arylboronic acids. The coupling of a wide array of aromatic halides with arylboronic acids with the PdCl₂-2 catalyst system gave good to excellent yields. The effective palladium loading could be as low as 0.0001 mol% and 0.01-0.1 mol% for iodide and bromide substrates, respectively. The coupling of unactivated aromatic chlorides with arylboronic acids also gave good results using Cs₂CO₃ as base with a 2 mol% palladium loading. The electronic factors from aromatic halides exert a significant influence on the Suzuki coupling catalyzed by the PdCl₂-2 system while the electronic effect from the arylboronic counterparts is negligible. The aromatic halides with modest steric hindrance could also couple smoothly with phenylboronic acids using the PdCl₂-2 catalyst system.     

Synthesis,characterization and antitumor activity of palladium(II) complexes of monoethyl 8-quinolylmethylphosphonate

The complex-forming properties of monoethyl 8-quinolylmethylphosphonate (8-Hmqmp) towards palladium(II) ion have been investigated by reactions of the hydrochloride, 8-Hmqmp · HCl · H₂O, and sodium salt, Na(8-mqmp) · 2H₂O, of this monoester with palladium(II) halide compounds in aqueous solution over a wide pH range. Depending on pH and initial quinolinium and palladium salts, four types of complexes have been formed. Under acidic solution the ion-pair salt complexes [8-H₂mqmp]₂[PdX₄] (1 and 2, pH < 3) and [8-H₂mqmp]₂[Pd₂X₆] (3 and 4, pH ∼ 3), with protonated quinoline ligand as cation and tetrahalopalladate or hexahalodipalladate complex as anion (X = Cl, Br), were isolated. By heating in methanol the chloro complexes 1 and 3 as well as bromo complexes 2 and 4 were converted into the quinolinium salt complexes, [8-H₂mqmp][Pd(8-Hmqmp)X₃], 5 and 6, respectively, containing as anion the quinoliniummethylphosphonatetrihalopalladate complex with palladium bonded at the phosphonic acid moiety. The chelate complex 7, [Pd(8-mqmp)₂], with ligand bonded through the quinoline nitrogen and the deprotonated phosphonic acid oxygen and forming two seven-membered {N,O} chelate rings, was obtained in neutral and basic media. The complexes were identified and characterized by elemental analysis, magnetic and conductance measurements, spectroscopic studies (IR, ¹H NMR, UV–Vis, positive/negative ion FAB MS) and thermal analysis (TG, DTA). As a preliminary screening for their biological activity, complexes were investigated for their ability to inhibit the cancer growth in vitro in the human KB and murine L1210 cell lines. The results obtained were compared with those obtained for the complexes of diethyl 8-quinolylmethylphosphonate (8-dqmp) and monoethyl 2-quinolylmethylphosphonate (2-Hmqmp), and structural factors that determine the complex activity were discussed.     

Synthesis of palladium nanoparticles on organically modified silica: Application to design of a solid-state electrochemiluminescence sensor for highly sensitive determination of imipramine

Organically modified silica substrate containing amine and vinyl functional groups were used for reduction and stabilization of palladium nanoparticles. Uniform spherical nanoparticles of palladium with average diameter of 10 nm were formed on silica substrate by direct contact of the substrate with an aqueous solution of palladium precursor, without the addition of any chemical reducer. Moreover, a sensitive and selective solid state electrochemiluminescence sensor was fabricated for the determination of imipramine, based on Ru(bpy)₃²⁺-palladium nanoparticles doped carbon ionic liquid electrode. In this process, imipramine acts as a co-reactant for Ru(bpy)₃²⁺. It is believed that the enhancement of the electrochemiluminescence signal in the presence of palladium nanoparticles in the composite is due to palladium catalytic effect on electrochemical and also chemical process involved in formation of Ru(byp)₃²⁺*. In addition, the results confirmed that, the rigid composite electrode shows the characteristic of microelectrode arrays. The proposed method was applied to the determination of imipramine in tablets and urine samples. The electrochemiluminescence intensity showed good linearity with the imipramine concentration from 1–100 pM, with a detection limit of 0.1 pM.     

Synthesis, structures and photoluminescence behavior of some group 10 metal alkynyl complexes derived from 3-(N-carbazolyl)-1-propyne

A new class of luminescent and thermally stable mononuclear group 10 platinum(II) and palladium(II) acetylides trans-[Pt(PR₃)₂(L)₂] (R = Bu, Et) and trans-[Pd(PBu₃)₂(L)₂] (LH = 3-(N-carbazolyl)-1-propyne) have been successfully synthesized and characterized. The structural properties of these discrete metal complexes have been studied by X-ray crystallography. We report their optical absorption and photoluminescence spectra and interpret the results in terms of the nature of the metal center and the type of phosphines used. Our investigations indicate that they display heavy metal-enhanced phosphorescence bands at 77 K and we find that the platinum complexes afford more intense triplet emission than that for the palladium congener, consistent with the stronger heavy-atom effect of the third row element than the second row neighbor of the same group.     

Osmium (VI) catalyzed chemoselective oxidation of allylic and benzylic alcohols

A mild and highly chemoselective approach to oxidation of allylic, electron rich/deficient benzylic, and heterocyclic alcohols employing catalytic quantities of K₂[OsO₂(OH)₄] (3 mol %) and chloramine-T (50 mol %) is described. The protocol offers short reaction times (25 min–2 h), controlled oxidation, and tolerance to a variety of substrates. A systematic mechanistic study based on the LC-ESI-MS/MS reveals the presence of imidotriooxoosmium species which further reacts with alcohol to give the oxidized product.     

A simple one-pot procedure for the direct conversion of alcohols into azides using TsIm

A facile and efficient method for one-pot conversion of alcohols into azides using N-(p-toluenesulfonyl)imidazole (TsIm) is described. In this method, alcohols are refluxed with a mixture of NaN₃, TsIm and triethylamine in the presence of catalytic amounts of tetra-n-butylammonium iodide (TBAI) in DMF affording the corresponding alkyl azides in good yields. This methodology is highly efficient for various structurally diverse alcohols with selectivity for ROH: 1° > 2° > 3°.