Pd CN Research Articles

Three-Dimensional Porous Carbon/Nitrogen Framework-Decorated Palladium Nanoparticles for Stable and Wide-Concentration-Range Hydrogen Sensing.

Hydrogen (H2) as a high-energy-density carrier is of great potential in the upcoming hydrogen economy. Nevertheless, H2/air mixtures are explosive at H2 concentrations above 4 v/v % and reliable and wide-concentration-range H2 sensors are thus highly desired. Here, hydrogen sensing has been developed using palladium nanoparticles of ∼11.2 nm in diameter chemically decorated on the carbon/nitrogen three-dimensional porous framework of 308 m2 g-1 in specific surface area (Pd NPs@CN 3D framework). Theoretically, the Pd NPs and CN 3D framework are used to construct the Mott-Schottky heterojunctions, in which the CN 3D framework possesses a higher work function, promoting electron transfer to Pd NPs and therefore highly active dissociation of H2. Beneficially, the Pd NPs@CN 3D framework exhibits a wide concentration range of 200 ppm (S ≈ 0.2% and Tres ≈ 15 s) to 40 v/v % (S ≈ 73.8% and Tres ≈ 9 s) H2 sensing at room temperature. Remarkably, the H2 sensor prototype built with the Pd NPs@CN 3D framework shows excellent long-term stability that maintains reliable H2 sensing after 142 days. Such stable hydrogen sensing provides an experimental basis for the wide-concentration-range detection of H2 leakage in the future hydrogen economy.

Impairment of the visuospatial working memory in the patients with Parkinson\u2019s Disease: an fMRI study

BackgroundMild cognitive impairment (MCI) is a common symptom in the patients with Parkinson’s disease (PD). The characteristics of cognitive impairment in PD are executive function (including working memory) and visuo-perceptual processing. The visuospatial n-back test has the merit of minimizing the influence of educational biases involved in the verbal n-back test. Furthermore, it can assess both visuospatial recognition and working memory in a single test.MethodsWe aimed to clarify the advantage of the visuospatial n-back test as a tool for detecting impairments of working memory in PD. We enrolled 28 right-handed patients with PD (18 males, 10 females) and 12 age-matched healthy controls (HC; 7 males, 5 females). Thirteen patients were classified as MCI (PD-MCI), and 15 as cognitively normal PD (PD-CN). Using functional MRI (fMRI), we explored the specific brain regions associated with the performance of the n-back test in the PD-MCI, PD-CN, and HC groups. The 0-back test assesses visuospatial recognition, while the 1-back and 2-back tests assess visuospatial working memory. Group comparisons were performed for three loads of this test.ResultsPatients with PD performed significantly worse in terms of the correct answer rates of all n-back tests compared with HC. fMRI analyses performed during the 2-back test revealed reduced activation in the bilateral dorsolateral prefrontal cortex, middle frontal gyrus (MFG), and parietal lobule in the PD group compared with the HC group. In contrast, the fMRI result during the 0-back test showed only a marginal difference in the frontal lobe. On comparisons of task performance between the PD-MCI and PD-CN groups, we found that the correct answer rate in the 2-back test was lower in the PD-MCI group than in the PD-CN group. However, scores of the 0-back and 1-back tests were not significantly different between the two groups. The fMRI findings revealed that activations within the middle frontal gyrus (MFG) and inferior parietal lobule (IPL) during the 2-back test were reduced in the patients with PD-MCI when compared to those with PD-CN.ConclusionsThis study reports reduced activation of the MFG and IPL in patients with PD-MCI. These regions may be associated with the pathophysiology of working memory impairment in patients with PD, which involves fronto-striatal network dysfunction.

Regional Neural Activity Changes in Parkinson’s Disease-Associated Mild Cognitive Impairment and Cognitively Normal Patients

PurposeThe aim of this study was to compare regional homogeneity (ReHo) changes in Parkinson’s disease mild cognitive impairment (PD-MCI) patients with respect to normal controls (NC) and those with cognitively normal PD (PD-CN). Further, the study investigated the relationship between ReHo changes in PD patients and neuropsychological variation.Patients and MethodsThirty PD-MCI, 19 PD-CN, and 21 NC subjects were enrolled. Resting state functional magnetic resonance imaging data of all subjects were collected, and regional brain activity was measured for ReHo. Analysis of covariance for ReHo was determined between the PD-MCI, PD-CN, and NC groups. Spearman rank correlations were assessed using the ReHo maps and data from the neuropsychological tests.ResultsIn comparison with NC, PD-CN patients showed significantly higher ReHo values in the right middle frontal gyrus (MFG) and lower ReHo values in the left supramarginal gyrus, bilateral inferior parietal lobule (IPL), and the right postcentral gyrus (PCG). In comparison with PD-CN patients, PD-MCI patients displayed significantly higher ReHo values in the right PCG, left middle occipital gyrus (MOG) and IPL. No significant correlation between ReHo indices and the neuropsychological scales was observed.ConclusionOur finding revealed that decreases in ReHo in the default mode network (DMN) may appear before PD-related cognitive impairment. In order to preserve executive attention capacity, ReHo in the right MFG in PD patients lacking cognition impairment increased for compensation. PD-MCI showed increased ReHo in the left MOG, which might have been caused by visual and visual-spatial dysfunction, and increased ReHo in the left IPL, which might reflect network disturbance and induce cognition deficits.

Crystal Structure of Mixed-metal Complex of Paddle-wheel-type Dinuclear Ruthenium(II,III) Carboxylate and Tetracyanidopalladate(II)

The crystal structure of mixed-metal complex of ruthenium propionate and tetracyanidopalladate(II), [{Ru2(C2H5CO2)4}2Pd(CN)4]n, was determined by the single-crystal X-ray diffraction method at 90 K. It crystallizes in the triclinic space group P1 with a = 9.8123(16)Å, b = 11.961(2)Å, c = 17.645(3)Å, α = 90.007(3), β = 90.634(3), γ = 108.285(2)°, V = 1966.2(6)Å3, Dx = 2.026 g/cm3, and Z = 2. The R1 [I > 2σ(I)] and wR2 (all data) values are 0.0788 and 0.1499, respectively, for all 8847 independent reflections. In the crystal, paddle-wheel-type dinuclear ruthenium cores are connected by tetracyanidopalladate(II) ions in an alternate arrangement to form a two-dimensional sheet constructed of 28-membered [–Ru2–NC–Pd–CN–]4 rings.

M-Carborane-Based Chiral NBN Pincer-Metal Complexes: Synthesis, Structure, and Application in Asymmetric Catalysis

We have succeeded in synthesizing m-carborane-based chiral NBN-pincer ligands, 1,7-bis(oxazolinyl)-1,7-dicarba-closo-dodecaborane (Carbox) (7-9). The combination of bis(hydroxyamides) and 3 equiv of diethylaminosulfur trifluoride (DAST) is a key step for cyclization to form oxazoline rings in excellent yields. X-ray crystal structures of these ligands confirmed three donor sites, one central B and two flanking N atoms in fixed positions. The electrophilic halogenation of the Carbox pincer ligands with iodine and a catalytic amount of Lewis acid led to ring-opening of the oxazolines and afforded bis(haloamides) (13 and 14). The air- and moisture-stable Carbox pincer complexes of rhodium(III), nickel(II), and palladium(II) were synthesized by the oxidative addition of RhCl(3)·3H(2)O, Ni(COD)(2), and Pd(CH(3)CN)(4)[BF(4)](2) to the Carbox pincer ligands (7-9), respectively. The catalytic activity of the rhodium(III) complexes (18-20) was examined for the asymmetric conjugate reduction of α,β-unsaturated esters and reductive aldol reaction. Among these catalysts, [(S,S)-Carbox-iPr]Rh(OAc)(2)·H(2)O (18) showed the highest enantioselective catalytic ability for both asymmetric conjugate reduction and reductive aldol reaction.

A Novel, Air-Stable Phosphine Ligand for the Palladium-Catalyzed Suzuki−Miyaura Cross-Coupling Reaction of Chloro Arenes

A novel, air-stable phosphine ligand, prepared from readily available 2-bromonitrobenzene and vinylmagnesium bromide, combines with Pd(CH(3)CN)(2)Cl(2) to afford an effective catalyst for Suzuki-Miyaura cross-coupling of aryl, heteroaryl, and allyl chlorides with phenylboronic acid.

Selective Formation of β-O-Aryl Glycosides in the Absence of the C(2)-Ester Neighboring Group

The development of a general and practical method for the stereoselective synthesis of beta-O-aryl glycosides that exploits the nature of a cationic palladium(II) catalyst, instead of a C(2)-ester directing group, to control the beta-selectivity is described. This beta-glycosylation reaction is highly diastereoselective and requires 2-3 mol % of Pd(CH(3)CN)(4)(BF(4))(2) to activate glycosyl trichloroacetimidate donors at room temperature. The current method has been applied to d-glucose, d-galactose, and d-xylose donors with a nondirecting group incorporated at the C(2)-position to provide the O-aryl glycosides with good to excellent beta-selectivity. In addition, its application is widespread to electron-donating, electron-withdrawing, and hindered phenols. The reaction is likely to proceed through a seven-membered ring intermediate, wherein the palladium catalyst coordinates to both C(1)-trichloroacetimidate nitrogen and C(2)-oxygen of the donor, blocking the alpha-face. As a result, the phenol nucleophile preferentially approaches to the top face of the activated donor, leading to formation of the beta-O-aryl glycoside.

Cationic Palladium(II)-Catalyzed Stereoselective Glycosylation with Glycosyl Trichloroacetimidates

The development of a new method for stereoselective glycosylation with glycosyl trichloroacetimidate donors employing cationic palladium(II), Pd(CH(3)CN)(4)(BF(4))(2), is described. This process employs Pd(CH(3)CN)(4)(BF(4))(2) as an efficient activator, providing access to a variety of disaccharides and glycopeptides. This reaction is highly stereoselective and proceeds under mild conditions with low catalyst loading. Interestingly, this palladium catalysis directs beta-glucosylations in the absence of classical neighboring group participation.

Stepwise assembly of linearly-aligned Ru–M–Ru (M = Pd, Pt) heterotrimetallic complexes with σ-4-ethynylpyridine spacer

Two heterotrinuclear oligomeric complexes [trans-RuCl(C[triple bond, length as m-dash]Cpy-4)(dppm)(2)](2)[MCl(2)] (M = Pd ; M = Pt ) are prepared from the metalloligand trans-[RuCl(C[triple bond, length as m-dash]Cpy-4)(dppm)(2)] (dppm = Ph(2)PCH(2)PPh(2), ). The resultant linear alignment of the metals [Ru-M-Ru] is imposed by a combinative use of trans-directed spacers and planar metals with trans-juxtaposed donor sites. Ligand exchange of with [Pd(CH(3)CN)(4)][PF(6)](2) gives trans-[Ru(CH(3)CN)(C[triple bond, length as m-dash]Cpy-4)(dppm)(2)][PF(6)] (). All complexes are characterized by single-crystal X-ray crystallography and solution spectroscopy. Acid-base titration on suggested protonation of the pendant pyridyl. Complexes and also undergo protonation at the C[triple bond, length as m-dash]C moiety under acid conditions. The inter-conversion of alkynyl and vinylidene functionality is described. The dual acid and base characters of makes it a potential metalloligand towards basic and acidic fragments in multinuclear heterometallic assemblies.

A Highly Active Palladium Catalyst for Intermolecular Hydroamination. Factors that Control Reactivity and Additions of Functionalized Anilines to Dienes and Vinylarenes

We report a catalyst for intermolecular hydroamination of vinylarenes that is substantially more active for this process than catalysts published previously. With this more reactive catalyst, we demonstrate that additions of amines to vinylarenes and dienes occur in the presence of potentially reactive functional groups, such as ketones with enolizable hydrogens, free alcohols, free carboxylic acids, free amides, nitriles, and esters. The catalyst for these reactions is generated from [Pd(eta(3)-allyl)Cl](2) (with or without added AgOTf) or [Pd(CH(3)CN)(4)](BF(4))(2) and Xantphos (9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene), which generates complexes with large P-Pd-P bite angles. Studies on the rate of the C-N bond-forming step that occurs by attack of amine on an eta(3)-phenethyl and an eta(3)-allyl complex were conducted to determine the effect of the bite angle on the rate of this nucleophilic attack. Studies on model eta(3)-benzyl complexes containing various bisphosphines showed that the nucleophilic attack was faster for complexes containing larger P-Pd-P bite angles. Studies of substituted unsymmetrical and unsubstituted symmetrical model eta(3)-allyl complexes showed that nucleophilic attack on complexes ligated by Xantphos was faster than on complexes bearing ligands with smaller bite angles and that nucleophilic attack on unsymmetrical allyl complexes with larger bite angle ligands was faster than on unsymmetrical allyl complexes with smaller bite angle ligands. However, monitoring of catalytic reactions of dienes by (31)P NMR spectroscopy showed that the concentration of active catalyst was the major factor that controlled rates for reactions of symmetrical dienes catalyzed by complexes of phosphines with smaller bite angles. The identity of the counterion also affected the rate of attack: reactions of allylpalladium complexes with chloride counterion occurred faster than reactions of allylpalladium complexes with triflate or tetrafluoroborate counterion. As is often observed, the dynamics of the allyl and benzyl complexes also depended on the identity of the counterion.

Highly diastereoselective formation of C2-symmetric bis-thioglycoside Pd(II) complexes: the role of the exo anomeric effect.

Treatment of several C(2) symmetric bis-thioglycosides with Pd(CH(3)CN)(2)Cl(2) always leads to a single diastereomeric Pd(II) complex as a consequence of the exo-anomeric effect.

Cascade cyclization: an easy access to highly unsaturated polycyclic ring systems through a tandem stille/[4 + 2] reaction under mild conditions.

The synthesis of several polycyclic compounds 1a-c, 2, and 3 has been performed through a tandem Stille/[4 + 2] cascade reaction from cyclic bis(enoltrifluomethanesulfonate) 4a-c, 5, and 6, respectively. The reaction proceeds very efficiently in a one-pot operation at roomtemperature in DMF in the presence of a catalytic amount of Pd(CH(3)CN)(2)Cl(2) and LiCl.[reaction: see text]

Predominant 1,2-insertion of styrene in the Pd-catalyzed alternating copolymerization with carbon monoxide.

The regioselectivity of styrene insertion to an acyl-Pd bond was studied by NMR in (i) a stoichiomeric reaction and (ii) a copolymerization with CO. In the stoichiometric reaction of styrene with [(CH(3)CO)Pd(CH(3)CN)[(R,S)-BINAPHOS]].[B[3,5-(CF(3))(2)C(6)H(3)](4)], both 1,2- and 2,1-products were given. To mimic the real polymerization conditions, a polyketone-substituted complex [[CH(3)(CH(2)CHCH(3)CO)(n)]Pd[(R,S)-BINAPHOS]].[B(3,5-(CF(3))(2)C(6)H(3))(4)] (n approximately 14) was prepared. When this polymer-attached Pd species was treated with styrene, the 1,2-insertion product was the only detectable species. Thus, exclusive 1,2-insertion is demonstrated to be responsible for the styrene-CO copolymerization, in sharp contrast to the predominant 2,1-insertion with conventional nitrogen ligands. Chain-end analysis revealed that beta-hydride elimination took place from the 2,1-complex but not from the 1,2-complex. Thus, once 2,1-insertion occurs, rapid beta-hydride elimination proceeds to terminate the polymerization, as is common to the other phosphorus-ligand systems. The resulting Pd-H species re-initiates the copolymerization, as was proven by MALDI-TOF mass analysis of the product copolymers.

Chiral Palladium(II)-catalyzed asymmetric glyoxylate-Ene reaction: alternative approach to the enantioselective synthesis of alpha-hydroxy esters

An effective chiral palladium catalyst [Pd(CH(3)CN)(2)(S)-Tol-BINAP](SbF(6))(2) (2b) is developed for asymmetric glyoxylate-ene reactions. This palladium dicationic catalyst provides a simple but efficient approach to the asymmetric synthesis of alpha-hydroxy esters in excellent yields with high enantioselectivities at relatively higher reaction temperature (60 degrees C).

Enantioselective Ring Opening of Aza and Oxabicyclic Alkenes with Dimethylzinc.

A system for efficient, asymmetric alkylative ring opening of azabenzonorbornadienes and [2.2.1] and [3.2.1] oxabicyclic alkenes was developed. The use of Pd(CH(3)CN)(2)Cl(2) and chiral phosphinooxazoline ligands gives the dihydronaphthalenes, cyclohexenols, and cycloheptenols in excellent yields and enantiomeric excesses.

Kinetics of nucleophilic attack by anilines on the nitrile group in palladium(II) [formula omitted]-cyanobenzyl complexes

A kinetic study of the reactions of anilines with the dimeric cationic complex of palladium(II) [Pd( o -CH 2C 6H 4CN)(PPh 3) 2] 2(BF 4) 2 emphasized the production of amidino mononuclear complexes through the breaking of the PdCN bonds, and the formation of an intermediate with the activate nitrile group where the amine reacts through an analogous two-step mechanism for both primary and secondary anilines.

Preparation of mononuclear and polynuclear cyano-complexes of palladium(II)

The abstraction of one cyanide ion from [Pd(dpe)CN) 2] (dpe = Ph 2PCH 2CH 2PPh 2) with silver perchlorate in acetonitrile solution yields a complex that has the empirical formula [Pd(dpe)CN]ClO 2 and is believed to be a mixture of two planar tetramers 4 and 5 both of which involve linear PdCNPd bridges. One of the tetramers has an idealised C 4h structure each palladium having a P 2CN environment, and the other has an idealised D 2h structure two of the palladiums having P 2C 2 environments and two having P 2N 2 environments.