An efficient aerobic oxidative phosphonation of a-amino CH bonds over CoNiFe hydrotalcite

An efficient and convenient heterogeneous catalytic procedure has been developed for the phosphonation of a-amino CH bonds with various dialkyl phosphites and diarylphosphine oxides using molecular oxygen as a sustainable oxidant over CoNiFe hydrotalcite. The catalytic system could tolerate various tetrahydroquinoline derivatives, and the corresponding a-amino phosphonic compounds could be obtained in good to excellent yields. Synergistic effect might exist in the oxidative phosphonation under the catalysis of CoNiFe hydrotalcite.     

Phosphonation of arenes with dialkyl phosphites catalyzed by Mn(II)/Co(II)/O2 redox couple

[reaction: see text]. Arylphosphonates were first synthesized through a catalytic phosphonation of various arenes with dialkyl phosphites under the influence of an Mn(OAc)2/Co(OAc)2/O2 redox couple. For instance, the reaction of benzene with diethyl phosphite in the presence of Mn(OAc)2 (5 mol %) and Co(OAc)2 (1 mol %) under a mixed gas of O2 (0.5 atm) and N2 (0.5 atm) at 45 degrees C led to diethyl phenylphosphonate in 81% selectivity at 62% conversion. This is the first successful phosphonation of benzene with dialkyl phosphites through a catalytic radical process.     

Synthesis of Baylis–Hillman-Derived Phosphonated 3-(Benzylaminomethyl)coumarins

Treatment of Baylis–Hillman-derived 3-(chloromethyl)coumarins with benzylamine has afforded benzylamino derivatives, sequential chloroacetylation and Michaelis–Arbuzov phosphonation of which have provided access to a series of phosphonate esters as potential HIV-1 protease inhibitors.     

3-Substituted Anilines as Scaffolds for the Construction of Glutamine Synthetase and DXP-Reductoisomerase Inhibitors

Access to a series of truncated ATP analogs, as potential anti-tuberculosis agents, has been explored via alkylation and acylation of 3-aminophenol, whereas chloroacetylation, using chloroacetyl chloride, and subsequent Arbuzov phosphonation of a series of 3-substituted anilines have afforded a series of phosphonate derivatives as potential antimalarial agents.     

Cross-dehydrogenative coupling strategy for phosphonation and cyanation of secondary N-alkyl anilines by employing 2,3-dichloro-5,6-dicyanobenzoquinone

The cross-dehydrogenative coupling strategy for metal-free phosphonation and cyanation of secondary N-alkyl anilines has been developed firstly under mild reaction conditions. Based on detailed optimization of reaction conditions, the substrate generality of N-alkyl anilines and various hydrogen phosphonates has been investigated, and a series of versatile α-aminophosphonates and α-aminonitriles were therefore furnished in good to excellent yields. A plausible collective reaction mechanism through dehydrogenation to imine formation, then to respective α-aminophosphonates and α-aminonitriles was proposed.     

Synthesis of self-doped polyaniline bearing phosphonic acid moiety via Pd-catalyzed phosphonation of poly(2-bromoaniline)

Self-doped conducting polyaniline bearing phosphonic acid moiety was synthesized via the Pd-catalyzed phosphonation of poly(2-bromoaniline) as a key reaction.     

Synthesis of Enaminone‐Pd(II) Complexes and Their Application in Catalysing Aqueous Suzuki‐Miyaura Cross Coupling Reaction

A series of Pd(II)‐enaminone complexes, termed Pd(eao)₂, have been synthesized and characterized. The investigation on the catalytic activities of these new Pd(II)‐reagents has proved that the Pd(eao)₂‐ 1 possesses excellent catalytic activity for the Suzuki‐ Miyaura cross coupling reactions of aryl bromides/chlorides with aryl/vinyl boronic acids in the environmentally benign media of aqueous PEG400 at low loading (5 mol‰). The superiority of this Pd(II)‐reagent to those commercial Pd(II) and Pd(0) catalysts in catalyzing the reactions has been confirmed by parallel experiments. What's more, Pd(eao)₂‐ 2 has been found as a practical catalyst for the homo‐coupling reactions of aryl boronic acids.     

Palladium‐catalyzed phosphonation of SEBS block copolymer

Phosphonic acid‐bearing styrene–ethylene/butylene–styrene (SEBS) block copolymer was synthesized by bromination and subsequent palladium‐catalyzed phosphonation of SEBS. The phosphonated block copolymer was characterized by spectroscopic, thermal, and conductivity measurements. The new polymer shows good ion‐exchange capacity of ～0.7 meq/g and proton conductivity of around 2–4 mS/cm (at room temperature and 100% relative humidity) which is in good agreement with literature value of other phosphonated materials. This value was obtained despite a relatively low degree of phosphonation, demonstrating the ability of the phase separated nature of block copolymers to promote proton conductivity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5431–5441, 2008     

甲酸在钯微粒修饰聚苯胺电极上氧化的协同效应研究

Electrochemical oxidation of formic acid on PAN(Pd) electrode has been studied using conventional electrochemical techniques and the electrochemical in-situ FTIR. The process of electrochemical oxidation of PAN(Pd) electorde has been put forward. The kinetic parameters of different thickness of PAN film such as diffusion coefficient (D0) and reaction rate constant(k0) have been calculated. Furthermore, the causes of the difference between PAN(Pd) and pure Pd(or Pt) electrodes as well as the high electrocatalytic activation of PAN(Pd) electrode for oxidation of fomic acid have also been discussed. The high catalytic activation of PAN(Pd) electrode for oxidation of formic acid probably comes from the synergistic effect of the subcatalytic interaction of PAN and the catalytic interaction of the palladium microparticles.     

Synthesis of phenanthridin-6-yldiphenylphosphine oxides by oxidative cyclization of 2-isocyanobiphenyls with diarylphosphine oxides

A Mn(III)-promoted oxidative cyclization of 2-isocyanobiphenyls with diarylphosphine oxides is reported, providing phenanthridin-6-yldiphenylphosphine oxides in good yields. Radical phosphonation and isocyanide insertion are believed to be involved in the reaction process.     

Connecting binuclear Pd(III) and mononuclear Pd(IV) chemistry by Pd-Pd bond cleavage

Oxidation of binuclear Pd(II) complexes with PhICl(2) or PhI(OAc)(2) has previously been shown to afford binuclear Pd(III) complexes featuring a Pd-Pd bond. In contrast, oxidation of binuclear Pd(II) complexes with electrophilic trifluoromethylating ("CF(3)(+)") reagents has been reported to afford mononuclear Pd(IV) complexes. Herein, we report experimental and computational studies of the oxidation of a binuclear Pd(II) complex with "CF(3)(+)" reagents. These studies suggest that a mononuclear Pd(IV) complex is generated by an oxidation-fragmentation sequence proceeding via fragmentation of an initially formed, formally binuclear Pd(III), intermediate. The observation that binuclear Pd(III) and mononuclear Pd(IV) complexes are accessible in the same reactions offers an opportunity for understanding the role of nuclearity in both oxidation and subsequent C-X bond-forming reactions.     

Ab initio study of Pd-decorated single-walled carbon nanotube with C-vacancy as CO sensor

In this paper, the adsorption of CO onto Pd-decorated (5,5) single-walled carbon nanotube (Pd/SWCNT) and Pd-doped (5,5) single-walled carbon nanotube (Pd/SWCNT-V) has been investigated using ab initio studies. The larger binding energies and charges transfer show that the adsorption of CO onto Pd/SWCNT is more stable than that of CO onto Pd/SWCNT-V. The Pd/SWCNT can be utilized as good sensors for CO molecules due to strong binding energy and large electron charge transfer between the Pd/SWCNT and this molecule. Furthermore, the topological properties of the electron density distributions for intramolecular interactions have been analyzed in terms of the Bader theory of atoms in molecules. Finally, the natural population analysis method has been used to evaluate the Pd–C and Pd/CO interactions.     

Recoverable, reusable, highly active, and sulfur-tolerant polymer incarcerated palladium for hydrogenation

A new type of immobilized palladium, PI (polymer incarcerated) Pd (2b), from Pd(PPh(3))(4) and copolymer (1b) has been developed. The excellent activity of PI Pd has been demonstrated in hydrogenation of various olefins, benzyl ethers, and nitro and aromatic compounds. PI Pd is tolerant under high pressure and high temperature and can be recovered and reused several times without loss of activity even under harsh conditions. Moreover, PI Pd is highly resistant to poisoning by sulfur.     

Oxygen binding to [Pd(L)(L')] (L= NHC, L' = NHC or PR3, NHC = N-heterocyclic carbene). synthesis and structure of a paramagnetic trans-[Pd(NHC)2(η(1)-O2)2] complex

The reactivity of a number of two-coordinate [Pd(L)(L')] (L = N-heterocyclic carbene (NHC) and L' = NHC or PR(3)) complexes with O(2) has been examined. Stopped-flow kinetic studies show that O(2) binding to [Pd(IPr)(P(p-tolyl)(3))] to form cis-[Pd(IPr)(P(p-tolyl)(3))(η(2)-O(2))] occurs in a rapid, second-order process. The enthalpy of O(2) binding to the Pd(0) center has been determined by solution calorimetry to be -26.2(1.9) kcal/mol. Extension of this work to the bis-NHC complex [Pd(IPr)(2)], however, did not lead to the formation of the expected diamagnetic complex cis-[Pd(IPr)(2)(η(2)-O(2))] but to paramagnetic trans-[(Pd(IPr)(2)(η(1)-O(2))(2)], which has been fully characterized. Computational studies addressing the energetics of O(2) binding have been performed and provide insight into reactivity changes as steric pressure is increased.     

New cyclometallated precursors of unsubstituted N-phenylpyrazole [{Pd(phpz)(μ-X)}2] (X = AcO or OH) and study of their reactivity towards selected ligands

A new acetate-bridged dinuclear palladacycle with unsubstituted N-phenylpyrazole [{Pd(phpz)(μ-AcO)}(2)] 1 has been isolated and characterised, including an X-ray diffraction study. A survey of the Cambridge Structural Database (CSD) v. 5.31 looking for analogous dimeric C^N cyclopalladated complexes has been done, exploring the incidence of cisoid/transoid arrangements, the preferred conformation of the eight-membered ring formed in the double bridge, the Pd-Pd distance and the main factors that affect it. The reaction of 1 with NBu(4)OH yielded [{Pd(phpz)(μ-OH)}(2)] 2 that has shown to be a complementary precursor of 1 in terms of acid/base reactivity. In this sense, both 1 and 2 are also well differentiated from halide precursors available to date. The preparation of selected complexes with potential applications in several fields, [Pd(phpz)(O^N)] O^N = N-p-chlorophenylsalycilaldiminate (N-pClsal) 3, picolinic acid (pic) 4; 8-hydroxiquinolinate (oxin) 5; 2-pyrrole-carboxaldeydate (2-pcal) 6, [Pd(phpz)(O^O)] O^O = salycilaldehydate (sal) 7 acetylacetonate (acac) 8, [{Pd(phpz)(μ-N^S)}(2)] N^S = 2-mercapto-1-methylimidazolate (SMeimz) 11; [{Pd(phpz)(μ-N^O)}(2)] N^O = succinimidate (succ) 12; [{Pd(phpz)(μ-N^N)}(2)] (N^N = pyrazolate (pz) 13, has been achieved using 1 or 2 as starting materials in acid/base reactions. Dithiocarbamate [Pd(phpz)(S(2)CNEt(2))] 9 and dithiophosphate [Pd(phpz){S(S)P(OEt)(2)}] 10 derivatives have been synthesised in related reactions, and the reactivity of 1 against neutral phosphine ligands has also been tested with the preparation of [Pd(phpz)(AcO)(PPh(3))] 14. The crystal structures of compounds 7, 9, 11, 12 and 13 (this one obtained from a powder sample using synchrotron radiation) have also been established, and together with 1 are the first examples of complexes containing unsubstituted N-phenylpyrazole as cyclometallated backbone that have been deposited to date on the Cambridge Structural Database.     

Novel Pd(ii)-salen complexes showing high in vitro anti-proliferative effects against human hepatoma cancer by modulating specific regulatory genes

We have reported the synthesis of a novel salen ligand and its mononuclear Pd-salen complexes derived from 2-{[2-hydroxy-3-{[(E)-(2-hydroxyphenyl)methylidene]amino}propyl)imino]methyl}phenol. The newly synthesized and isolated Pd(ii) complexes have been identified and fully characterized by various physico-chemical studies viz., elemental analyses, IR, UV-Vis, (1)H, (13)C NMR spectroscopy, electron spray ionization mass spectrometry (ESI-MS) and TGA/DTA studies. The molecular structure of the salen ligand has been ascertained by single-crystal XRD and it is coordinated to Pd(ii) ion through two nitrogen and two oxygen atoms. The UV-Vis data clearly suggest a square-planar environment around both the Pd(ii) ions. The DNA binding studies of the synthesized compounds has been investigated by electron spectroscopy and fluorescence measurements. The results suggest that Pd(ii) complexes bind to DNA strongly as compared to the free ligand. The free salen ligand and its Pd(ii) complexes have also been tested against human hepatoma cancer cell line (Huh7) and results manifested exceptional anti-proliferative effects of the Pd(ii) complexes. The anti-proliferative activity of Pd(ii) complexes has been modulated by specific regulatory genes.     

Improvements in cross coupling reactions of hypervalent siloxane derivatives

[formula: see text] The scope of the palladium-catalyzed cross coupling reaction of aryl halides with phenyltrimethoxysilane has been expanded to include aryl bromides, heteroaryl bromides, and aryl chlorides. A more general Pd(0)-catalyst/ligand system has been developed to activate bromides: palladium(II) acetate (Pd(OAc)2) is activated with triphenylphosphine (PPh3) or tri-o-tolylphosphine (P(o-tol)3) (1:2 molar ratio of Pd:phosphine). Coupling of aryl chloride derivatives required addition of 2-(dicyclohexylphosphino)biphenyl (Buchwald's ligand) to Pd2dba3 (tris-(dibenzylideneacetone)dipalladium(0)) (1:1.5 molar ratio of Pd:phosphine).     

Synthesis of palladium nanoparticles by sonochemical reduction of palladium(II) nitrate in aqueous solution

The sonochemical synthesis of stable palladium nanoparticles has been achieved by ultrasonic irradiation of palladium(II) nitrate solution. The starting solutions were prepared by the addition of different concentrations of palladium(II) nitrate in ethylene glycol and poly(vinylpyrrolidone) (PVP). The resulting mixtures were irradiated with ultrasonic 50 kHz waves in a glass vessel for 180 min. The UV-visible absorption spectroscopy and pH measurements revealed that the reduction of Pd(II) to metallic Pd has been successfully achieved and that the obtained suspensions have a long shelf life. The protective effect of PVP was studied using Fourier transform infrared (FT-IR) spectroscopy. It has been found that, in the presence of ethylene glycol, the stabilization of the nanoparticles results from the adsorption of the PVP chain on the palladium particle surface via the coordination of the PVP carbonyl group to the palladium atoms. The effect of the initial Pd(II) concentration on the Pd nanoparticle morphology has been investigated by transmission electron microscopy. It has been shown that the increase of the Pd(II)/PVP molar ratio from 0.13 x 10(-3) to 0.53 x 10(-3) decreases the number of palladium nanoparticles with a slight increase in particle size. For the highest Pd(II)/PVP value, 0.53 x 10(-3), the reduction reaction leads to the unexpected smallest nanoparticles in the form of aggregates.     

Reactions of carbon monoxide with free palladium oxide clusters: strongly size dependent competition between adsorption and combustion

The gas phase reactions of carbon monoxide with small mass-selected clusters of palladium, Pd(x)(+) (x = 2-7), and their oxides, Pd(x)O(+) (x = 2-7) and Pd(x)O(2)(+) (x = 4-6), have been investigated in a radio frequency ion trap operated under multi-collision conditions. The bare palladium clusters were found to readily adsorb CO yielding a highly size dependent product pattern. Most interestingly, the reactions of the pre-oxidized palladium clusters with CO lead to very similar product distributions of Pd(x)(CO)(z)(+) complexes as in the case of the corresponding pure Pd(x)(+) clusters. Consequently, it has been concluded that the investigated palladium oxide clusters efficiently oxidize CO under formation of the bare clusters, which further adsorb CO molecules yielding the previously observed Pd(x)(CO)(z)(+) product complex distributions. This CO combustion reaction has been observed even at temperatures as low as 100 K. However, for Pd(2)O(+), Pd(6)O(+), Pd(6)O(2)(+), and Pd(7)O(+) a competing reaction channel yielding palladium oxide carbonyls Pd(x)O(CO)(z)(+) could be detected. The latter adsorption reaction may even hamper the CO combustion under certain reaction conditions and indicates enhanced activation barriers involved in the CO oxidation and/or the CO(2) elimination process on these clusters.     

(IPr)Pd(acac)Cl: an easily synthesized, efficient, and versatile precatalyst for C-N and C-C bond formation

A very straightforward synthesis of (IPr)Pd(acac)Cl from two commercially available starting materials, Pd(acac)2 and IPr.HCl [acac = acetylacetonate; IPr = N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene], has been developed. The resulting complex, (IPr)Pd(acac)Cl (1), has proven to be a highly active PdII precatalyst in the Buchwald-Hartwig and the alpha-ketone arylation reactions. A wide range of substrates has been screened, including unactivated, sterically hindered, and heterocyclic aryl chlorides.