Reactive Palladium Research Articles

Synthesis, Characterization, and Reactivity of Palladium(II) Salen and Oxazoline Complexes.

Two methods for the syntheses of palladium(II) salen complexes are described. The first involves template synthesis of the ligand in which bis(salicylaldehydato)palladium(II), 2, is initially synthesized and reacted with the appropriate diamine bridge to yield the desired palladium salen. The template synthesis approach suffers, however, from low overall yields (17-30%). Alternatively, treatment of bis(acetonitrile)palladium(II) chloride with the appropriate salen ligand under inert atmosphere yields the palladium salen complex in high yields (80-85%). [2-(2'-Hydroxyphenyl)-2-oxazolinato]palladium(II), 7, was also synthesized. All the palladium complexes were fully characterized spectroscopically. A single-crystal X-ray structure of 7 has been solved. In contrast to previous reports, complex 2 was found to be stable over weeks and remained suitable for the template syntheses. The catalytic activity of complex 2 in cyclopropanation of alkenes with ethyl diazoacetate (EDA) was investigated. The catalyst is not functional group tolerant and works best for styrene; turnover numbers (TON's) of 45 were achieved. The availability of an open coordination site seems to be a prerequisite for catalytic decomposition of EDA.

ChemInform Abstract: Role of dba in the Reactivity of Palladium(0) Complexes Generated in situ from Mixtures of Pd(dba)2 and Phosphines

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Palladium(II) allyl complexes with nitrogen–sulfur bidentate ligands. Substituent effects in the mechanism of allyl amination

The reactivity of palladium(II) allyl complexes containing the nitrogen–sulfur bidentate ligand N–SR (N–SR=2-(phenylthiomethyl)pyridine, 2-(phenylthiomethyl)-6-methylpyridine, 2-( tert-butylthiomethyl)pyridine) was studied in CHCl 3 in the presence of the activated olefin fumaronitrile (fn). The stepwise mechanism involves a fast pre-equilibrium in which the N–SR ligand is displaced by the amine with formation of an inert bis-amino allyl species and concomitant rate-determining bimolecular attack of the amine on the coordinated allyl moiety to give the allylamine and the olefin-stabilized Pd(0) complexes [Pd( η 2-fn)(N–SR)]. The influence of the substituents at the allyl fragment and at the nitrogen–sulfur ligand is rationalized together with the fluxional behavior in solution.

Unexpected bell-shaped effect of the ligand on the rate of the oxidative addition to palladium(0) complexes generated in situ from mixtures of Pd(dba) 2 and para-substituted triarylphosphines

As with PPh 3, mixtures of Pd(dba) 2 and n L (L = para-Z-substituted triphenylphosphines, n ≥ 2) in DMF lead to the formation of Pd(dba)L 2 and PdL 3 in equilibrium with PdL 2. The equilibrium between Pd(dba)L 2 and PdL 3 is more in favor of PdL 3 when the phosphine is less electron rich. In other words, the exchange of the dba ligand by a phosphine from Pd(dba)L 2 to form PdL 3 is more favored when the phosphine is less electron rich. The less ligated complex PdL 2 is the reactive species in the oxidative addition with phenyl iodide. It was therefore expected that the rate of the oxidative addition would increase when the phosphine is more electron rich. However, surprisingly, when the palladium(0) complex is generated from mixtures of Pd(dba) 2 and n L ( n ≥ 2), the oxidative addition does not follow a linear Hammett correlation and the reactivity of the palladium(0) complex exhibits a maximum value. This is due to two antagonist effects. Indeed, the overall reactivity in the oxidative addition is governed by two factors: the intrinsic reactivity of PdL 2 and its concentration. When the phosphine becomes more electron rich, the complex PdL 2 becomes more nucleophilic and its intrinsic reactivity in the oxidative addition increases. However, when the phosphine becomes more electron rich, the concentration of PdL 2 decreases because the equilibrium between the palladium(0) complexes becomes more in favor of Pd(dba)L 2. These results emphasize the crucial role of the dba ligand on the reactivity of palladium(0) complexes generated in situ in mixtures of Pd(dba) 2 and phosphines.

Palladium-ceria catalysts: Metal-support interactions and reactivity of palladium in selective hydrogenation of but-1-yne

The influence of palladium-ceria interactions on the reactivity of palladium in but-1-yne hydrogenation has been investigated and compared with previous results obtained on alumina. The main differences from Pd-alumina catalysts are (i) the enhancement of the turnover frequency ascribed to electron transfer from ceria to Pd, (ii) the diminution of the selectivity to but-1-ene, attributed to hydrogen spillover.

Interaction between lead iron niobate/tungstate ceramics and silver/palladium metals

The interactions between ferroelectric Pb(Fe 2 3 Nb 1 2 )O 3 (PFN)/ Pb(Fe 2 3 W 1 3 )O 3 (PFW) perovskite ceramics and silver/palladium metals were systematically investigated through the phase formation and microstructural variation. Silver did not react with PFN/PFW ceramics after heating to 900 °C, and perovskite grains were only distributed among the matrix of silver. After being heated with 70Ag/30Pd at 900 °C, no perovskite phases were significantly altered; however, in the PFN-rich ceramics, the palladium content in the alloy decreased along with the formation of PdO. Pure palladium was found to have the highest reactivity with PFN/PFW ceramics. The reactions between palladium and ceramics occurred vigorously from 850 °C and resulted in markedly different microstructures. Palladium caused PFW to decompose into PbWO 4 and Pb 2WO 5, and also led to the dissociation of PFN/PFW ceramics to produce pyrochlore phases and Fe 2C 3. The reactivity of palladium with perovskite phases was positively correlated with the PFN content in specimens. In addition, increasing the PFN content also tended to postpone the reduction process of PdO to palladium.

Bond selectivity in the dissociative adsorption of c-CH 2N 2 on single crystals: a comparative DFT-LSD investigation for Pd(110) and Cu(110)

A comparison between the reactivity of palladium and copper cluster models toward diazirine ( c-CH 2N 2) was made using the LCGTO-MCP-LSD method. Adsorption with the nitrogen pair directly over surface atoms (the μ-top site) is clearly more stable than when the NN pair is perpendicular to the rows of the (110) surface (the μ-bridge site). The NN bond is strongly affected by adsorption, a significant decrease of its bond order is observed for both palladium and copper. One main difference between palladium and copper with regards to the adsorption of c-CH 2N 2 is the magnitude of the MN bond order; palladium tends to form a stronger chemisorption bond than copper. A second difference is that partial occupation of the LUMO of diazirine only occurs for the copper cluster model systems. The concerted dissociation of CN bonds is energetically demanding but appears to be easier on Pd than on Cu by around 28 kcal mol −1. The study of electronically perturbed diazirine (excited, ionized or isomerized) provides insight on how chemisorption induces variations in bond lengths and vibrational frequencies as a result of charge transfer. The results of the calculations show that the μ-top adsorbed state is more similar to the n_ →π∗ first excited state of the free molecule than to the ionized state. A more striking result is obtained when the first excited states of the chemisorbed complexes are studied. A 0.4 eV electron excitation in the c- CH 2 N 2 Cu 4 complex (μ-top) leads to a significant decrease of the bond order of the NN bond but does not induce even a small change for the c- CH 2 N 2 Pd 4 complex. The calculations provide some insights on the markedly different bond scission selectivity observed in experimental studies of the thermal decomposition of diazirine on Pd and Cu surfaces. Experiments show that NN bond scission occurs with essentially 100% selectivity on copper, whereas NN bond retention as well as NN bond scission occurs on Pd(110).

Electron spin resonance and electron spin echo modulation spectroscopic studies on the structure and reactivity of palladium(I) species in SAPO-11 molecular sieves

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron spin resonance and electron spin echo modulation spectroscopic studies on the structure and reactivity of palladium(I) species in SAPO-11 molecular sievesChul Wee Lee, Jong Sung Yu, and Larry KevanCite this: J. Phys. Chem. 1992, 96, 19, 7747–7751Publication Date (Print):September 1, 1992Publication History Published online1 May 2002Published inissue 1 September 1992https://doi.org/10.1021/j100198a047RIGHTS & PERMISSIONSArticle Views97Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (590 KB) Get e-Alerts

Anomalous carbonylation of [Pd(dppm)(O 2CCF 3)] 2 to give an asymmetric μ-CO complex

The reactive palladium dimer, [Pd(dppm)(O 2CCF 3)] 2, is carbonylated to [Pd(dppm)(O 2CCF 3)] 2(μ-CO) in a reversible reaction with K = c. 7.2(2)x10 4 atm −1 ( P 1/2 = c. 2.4 Torr). This is significantly larger than is expected based on the λ max = 280 nm in the electronic spectrum. The product can be isolated in analytically pure form by crystallization under a CO atmosphere. It forms crystals in the monoclinic space group Cc with a = 18.584(5), b = 28.65(1), c = 11.164(3) Å and β = 95.16(2)°. The structure is significantly distorted. The bonding about the two palladium atoms is quite asymmetric. While one is close to a square planar geometry with a PdC(O) distance of 1.90(2) Å, the other is significantly pyramidalized and has a longer (2.00(2) Å) bond to the bridging CO. The PdPd distance is only 2.896(2) Å, much shorter than that usually observed for formally non-bonded Pd atoms.

Synthesis and reactivity of palladium and platinum complexes containing the bis(diphenylphosphino) methanide ligand

Complexes of general formulae [M(C 6X 5)(Ph 2PCHPPh 2)(L)] (M  Pd, Pt; X  F, Cl; L  PR 3, dppm(Ph 2PCH 2PPh 2)) have been obtained either by reaction of MCl(C 6F 5)(PR 3) 2 with dppm and NaH or with dppm-Li or reaction of [M(C 6F 5)(dppm)(PR 3)](ClO 4) with NaH. The complexes M(C 6X 5)(acac)(L) react with dppm to give analogous ddppm {[Ph 2PCHPPh 2] −} derivatives. Treatment of these complexes with HBF 4 gives of the corresponding dppm cationic derivatives. The complexes have been characterized by IR, 19F NMR, and 31P( 1H) NMR spectroscopy.

ChemInform Abstract: Competitive Hydrogenation of Butadiene and Butene on Palladium and Platinum Catalysts.

In a recent study of the selective hydrogenation of butadiene to butenes, the reactivity of palladium (in the form of single crystals and of supported catalysts) was compared with that of platinum. The reactivity of single-crystal faces with (111) orientation is comparable to that of SiO{sub 2}-supported catalysts. The argument put forward to explain the comparatively lower activity of platinum was its lower hydrogen coverage under a given pressure, in the presence of the hydrocarbons, arising from a heat of adsorption smaller than that on palladium (respectively 67 and 85 kJ/mol). Concerning its poorer selectivity toward butenes, the reason invoked was a similar heat of adsorption for butadiene and butenes: the olefinic intermediate compound remains partly on the surface and the reaction proceeds to butane. A powerful kinetic method which is able to provide direct evidence for this different adsorption of dienes and butenes would be the competitive hydrogenation of these two molecules. However, to distinguish between the ethylenic hydrocarbon formed during the reaction and the molecules already present in the reactants, the experiments were performed according to the sequence: competitive hydrogenation of a butadiene-propene mixture followed by the hydrogenation of a 1-butene-propene mixture. This paper describes a study whichmore » confirms that the reason for the selectivity of palladium (after stabilization of the catalyst) can be attributed unambiguously to its capacity of adsorbing a diene more strongly than an alkene molecule.« less

Competitive hydrogenation of butadiene and butene on palladium and platinum catalysts

In a recent study of the selective hydrogenation of butadiene to butenes, the reactivity of palladium (in the form of single crystals and of supported catalysts) was compared with that of platinum. The reactivity of single-crystal faces with (111) orientation is comparable to that of SiO{sub 2}-supported catalysts. The argument put forward to explain the comparatively lower activity of platinum was its lower hydrogen coverage under a given pressure, in the presence of the hydrocarbons, arising from a heat of adsorption smaller than that on palladium (respectively 67 and 85 kJ/mol). Concerning its poorer selectivity toward butenes, the reason invoked was a similar heat of adsorption for butadiene and butenes: the olefinic intermediate compound remains partly on the surface and the reaction proceeds to butane. A powerful kinetic method which is able to provide direct evidence for this different adsorption of dienes and butenes would be the competitive hydrogenation of these two molecules. However, to distinguish between the ethylenic hydrocarbon formed during the reaction and the molecules already present in the reactants, the experiments were performed according to the sequence: competitive hydrogenation of a butadiene-propene mixture followed by the hydrogenation of a 1-butene-propene mixture. This paper describes a study whichmore » confirms that the reason for the selectivity of palladium (after stabilization of the catalyst) can be attributed unambiguously to its capacity of adsorbing a diene more strongly than an alkene molecule.« less

Synthesis and reactivity of palladium(I) derivatives with bis(diphenylphosphino)amine. X-ray crystal structure of Pd 2(μ-dppa) 2Cl 2·(CH 3) 2CO

ClPd(μ-dppa) 2PdCl [dppa = bis(diphenylphosphino)aminel ( 1) has been prepared by treating PdCl 2(NCPh) 2 with Pd 2(dba) 3·.CHCl 3 (dba = dibenzylideneacetone) and dppa in CH 2Cl 2. Substitution reactions allow the synthesis of the neutral BrPd(μ-dppa) 2 PdBr ( 2) and the cationic [Ph 3PPd(μ-dppa) 2PdPPh 3](BPh 4) 2 ( 4) derivatives. Complex 1 reacts with SnCl 2 yielding Cl 3SnPd(μ-dppa) 2PdSnCl 3 ( 3). The species R 2N + and SO 2 insert into the PdPd bond of 1 to give the appropriate A-frame Pd II-Pd II complexes. Extrusion of SO 2 takes place at room temperature. CO does not react with 1 in CH 2Cl 2 at room temperature. The insertion-elimination reactions of 1 with isonitriles RNC (R = p-Tol Cy) have been studied. The molecular structure of ClPd(μ-dppa) 2PdCl·(CH 3) 2CO has been established by a single crystal X-ray study. The crystals are monoclinic, space group P2 1/ c, with a = 13.540(3), b = 16.943(2), c = 21.082(15) Å, β = 105.257(42)° and Z = 4. The final R factor was 0.033 for 5091 observed reflections. The PdPd distance is 2.6378(6) Å.

Macrocyclic complexes of the platinum metals

Abstract

ChemInform Abstract: Formation and Reactivity of Palladium(II) Sulfito Complexes in Aqueous Solution. Part 2. Kinetics and Mechanisms.

AbstractThe kinetics of the formation of the title complex (III) via the reaction of the aquo complex (I) with HSO3‐/SO32‐ are studied in detail as a function of pH, (total S), temp., and pressure.

ChemInform Abstract: Formation and Reactivity of Palladium(II) Sulfito Complexes in Aqueous Solution. Part 1. Spectroscopic Evidence for the Labilization of a Chelated Amine.

AbstractThe reactions of (I) and (III) with bisulfite or sulfite are studied as a function of pH and sulfite concentration with use of IR, UV/VIS and 1H and 13C NMR spectroscopy.

Formation and reactivity of palladium(II) sulfito complexes in aqueous solution. 2. Kinetics and mechanisms

Cinetique de formation de Pd(Et 4 dien)SO 3 . La loi de vitesse favorise un mecanisme d'anation qui met en jeu un preequilibre de formation du complexe

Formation and reactivity of palladium(II) sulfito complexes in aqueous solution. 1. Spectroscopic evidence for the labilization of a chelated amine

Etude des reactions de Pd(Et 4 dien)Cl + et Pd(Et 4 dien)OH 2 2+ avec bisulfite/sulfite. Formation de Pd(Et 4 dien)SO 3 stable a pH>7, mais se dechelatant a pH<6; la dechelation est reversible. Effet labilisant du sulfite coordine

ChemInform Abstract: STRUCTURE AND REACTIVITY OF PALLADIUM AND PLATINUM ARYLAZOOXIMATES

Chemischer InformationsdienstVolume 15, Issue 48 Reviews ChemInform Abstract: STRUCTURE AND REACTIVITY OF PALLADIUM AND PLATINUM ARYLAZOOXIMATES A. CHAKRAVORTY, A. CHAKRAVORTYSearch for more papers by this author A. CHAKRAVORTY, A. CHAKRAVORTYSearch for more papers by this author First published: November 27, 1984 https://doi.org/10.1002/chin.198448360AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume15, Issue48November 27, 1984 RelatedInformation

Structure and reactivity of palladium and platinum arylazooximates

The structure and selected reactions of the title compounds are reviewed. Some highlights are as follows (L = conjugate base of phenylazoacetaldoxime). While PtL2 exist in cis and trans forms, PdL2 occurs only in thetrans form. In the crystalline state cis-PtL2 consists of weakly held dimers (Pt. Pt 3.151 A) buttrans-PtL2 consists of stacks of discrete molecules in the solid state.Trans- PdL2 displays a surprisingly large tetrahedral distorsion. The different metal-ligand bonds undergo selective cleavage by different reagents. Thus HCl and tertiary phosphines respectively cleave the M-N (oxime) and M-N (azo) bonds. Phosphine cleavage leads to interesting situations such as cone angle-dependent equilibria and fluxional behaviour. A rich redox chemistry consisting of successive reductions of the azo groups and of the metal are revealed electrochemically.Cis-PtL2 unliketrans- PtL2 undergoes a facile one-electron oxidation at low potentials. Another very curious reaction of cis-PtL2 is the process in which an aromatic ring is thermally hydroxylated at the expense of an oximato oxygen atom. The meaning and significance of the observations are discussed.