Palladium Carbonyl Research Articles

Palladium carbonyl complexes with anions of N-heterocyclic carboxylic and pyridine-2-sulfonic acids

Synthesis, spectral characteristics, and structure of palladium(I) carbonyl complexes containing anions of N-heterocyclic carboxylic acids and pyridine-2-sulfonic acid of the general formula [Pd(CO)(NHC-CO2)]n/[Pd(CO)(NHC-SO3)]n, where NHC is an N-heterocycle, were described. The resulting complexes can be attributed to a binuclear structure with bridging or terminal coordination of carbonyl ligands depending on the nature of the substituents in the heterocycle.

Formation and Destruction of Palladium Carbonyl Nanoclusters in the Pd(II)–Cl––H+–H2O–CO Systems

Carbonyl palladium blacks are formed on treatment of Pd(II) chloride complex in a solution with carbon monoxide at ambient pressure and a temperature ≥20°C. The results of IR spectroscopy, powder X-ray diffraction, and electron microscopy demonstrated that carbonyl palladium blacks are heterogeneous unstable systems consisting of palladium, carbon, and oxygen, the ratio of which changes upon heat treatment. Palladium is present as the metal, the carbonyl cluster Pdx(CO)y, and the variable-composition PdCx phase, while carbon partly occurs as amorphous diamond with sp3 hybridization of atoms. After calcination of Pd black at 1000°C, a large amount of carbon remains in the resulting Pd sponge, which acquires abrasive properties. Dissolution of the sponge in aqua regia leaves a solid phase with a high carbon content

Palladium/Beta zeolite passive NOx adsorbers (PNA): Clarification of PNA chemistry and the effects of CO and zeolite crystallite size on PNA performance

Model 0.3 wt% and 1 wt% Pd/Beta was synthesized with nano-sized Beta crystals (average size <50 nm) and defect-free large micrometer sized crystals with similar Si/Al ratios ∼13 and 15. With the aid of FTIR we reveal the formation of at least two Pd(II)–NO and one Pd(I)–NO complexes upon NO adsorption on those materials under conditions relevant to PNA. Under higher NO pressures at room temperature, we detect the formation of the first palladium(II) dinitrosyl Pd(NO)2 complex, not observed previously on the solid supports or in organometallic compounds.O2 in dry streams promotes NO storage via additional formation of nitrosyl (NO+) ions; it also leads to stabilization of significant amounts of N2O3 in BEA pores. In the presence of water, NO storage capacity is dramatically lowered. However, in the presence of CO (which is always present in exhaust gas) the performance improves. With the aid of spectroscopy and PNA measurements we show that in the presence of CO, stable mixed palladium(II) carbonyl nitrosyl complex [Pd(II)(CO)(NO)] is formed and responsible for enhanced NOx storage. This points to a general conclusion that the species responsible for NOx storage on various zeolites in the presence of water and CO, are in fact, Pd(II)(CO)(NO).Decreasing the Pd loading to 0.3 wt% improves Pd dispersion and NO/Pd storage ratio. We also demonstrate that varying crystal sizes of BEA leads to significant changes in the NOx release temperature as well as NO/Pd ratio. Larger, defect free, more hydrophobic BEA crystals store more NOx and release it at higher temperature. Furthermore, larger, defect free and more hydrophobic BEA crystals stay significantly more active for PNA after hydrothermal aging, losing little activity compared with defective nanocrystals. High-field 27Al NMR results show that larger, hydrophobic BEA crystals are more resistant to de-alumination upon hydrothermal aging (HTA), and thus are more attractive for PNA storage with Pd.

Synthesis of 2-Alkynoates by Palladium(II)-Catalyzed Oxidative Carbonylation of Terminal Alkynes and Alcohols.

A homogeneous PdII catalyst, utilizing a simple and inexpensive amine ligand (TMEDA), allows 2‐alkynoates to be prepared in high yields by an oxidative carbonylation of terminal alkynes and alcohols. The catalyst system overcomes many of the limitations of previous palladium carbonylation catalysts. It has an increased substrate scope, avoids large excesses of alcohol substrate and uses a desirable solvent. The catalyst employs oxygen as the terminal oxidant and can be operated under safer gas mixtures.

Binary α-unsaturated palladium carboxylates and their complexes with morpholine derivatives: the Crystal structure of palladium carbamoyl crotonate (OC4H8NH)2Pd[OC4H8N(C=O)](MeCH=CHCO2) · H2O, a product of the first inner-sphere amination reaction of α-unsaturated palladium carbonyl carboxylates with morpholine

Binary α-unsaturated palladium carboxylates have been synthesized by substitution of α-unsaturated acids RCOOH (R is CH2=C(Me), MeCH=CH, PhCH=CH) for the acetate ion in Pd3(μ-MeCOO)6. These carboxylates react with amines A (A is morpholine (M), methylmorpholine (MM), or thiomorpholine (MS)) to give trans-Pd(A)2(RCOO)2 similar to trans-A2(MeCO2)2. The structures of the trans-Pd(A)2(RCOO)2 complexes (R is MeCH=CH; A is M, MM, MS) have been determined by X-ray crystallography. The effect of solvent on the crystal structure of the complexes has been demonstrated for trans-(MeCH=CHCO2)2Pd(C4H9NO)2 as an example. The amination reaction of palladium carbonyl crotonate with a secondary amine, morpholine, has been studied for the first time. The reaction involves disproportionation of Pd(I) into Pd(0) and Pd(II) and leads to the first unsaturated palladium(II) carbamoyl carboxylate—palladium carbamoyl crotonate trans-(OC4H8NH)2Pd[OC4H8NC(=O)](MeCH=CHCO2) · H2O, as well as to trans-M2Pd(MeCH=CHCO2)2 and (C4H10NO)+(MeCH=CHCO2)−. The structures of these compounds have been proved by X-ray crystallography.

The first carbamoyl–carboxylate complex of transition metals: Synthesis and structure of {(OC4H8NH)[OC4H8NC([dbnd]O)]Pd}2(μ-CMe3CO2)2

Reactions of palladium(I) carbonyl carboxylate complexes [Pd(μ-CO)(μ-RCO2)]n with secondary amines on the example of morpholine were studied. It was found that intramolecular carbonylation of amine in coordination sphere of polynuclear palladium species proceeds and binuclear palladium carbamoyl complex {(OC4H8NH)[OC4H8NC(O)]Pd}2(μ-RCO2)2 forms as a result. This is the first structurally characterized carbamoyl–carboxylate complex of transition metals. Also it was shown that morpholine itself and carboxylate-anions act as proton acceptors in the reaction of carbonylation of morpholine by coordinated CO.

Perfluoropropenyl-containing phosphines from HFC replacements.

A series of new perfluoropropenyl-containing phosphines of the type R3-nP(E-CF[double bond, length as m-dash]CFCF3)n (R = Ph, iPr, n = 1, 2; R = tBu, n = 2) have been prepared from the reaction of the hydrofluoroolefin Z-CF3CF[double bond, length as m-dash]CFH (HFO-1225ye) with base and the appropriate chlorophosphine, while reaction with Cl2PCH2CH2PCl2 gave (CF3CF[double bond, length as m-dash]CF)2PCH2CH2P(CF[double bond, length as m-dash]CFCF3)2, the first example of a bidentate perfluoroalkenyl-containing phosphine. An alternative route to these phosphines based on the room- or low-temperature deprotonation of CF3CF2CH2F (HFC-236ea) gives mainly the E-isomer, but also a small amount of the Z-isomer, the ratio of which depends on the reaction temperature. All of the phosphines could be readily oxidised with either H2O2 or urea·H2O2, and the phosphine selenides R3-nP(Se)(E-CF[double bond, length as m-dash]CFCF3)n (R = Ph, n = 1,2; R = iPr, n = 1; R = tBu, n = 2) were also prepared. The steric and electronic properties of these ligands were determined based on their platinum(ii), palladium(ii) and molybdenum carbonyl complexes. The crystal structures of (CF3CF[double bond, length as m-dash]CF)2PCH2CH2P(CF[double bond, length as m-dash]CFCF3)2, (CF3CF[double bond, length as m-dash]CF)2P(O)CH2CH2P(O)(CF[double bond, length as m-dash]CFCF3)2, iPr2P(Se)(CF[double bond, length as m-dash]CFCF3)2, trans-[PtCl2{Ph(3-n)P(E-CF[double bond, length as m-dash]CFCF3)n}2] (n = 1 or 2), trans-[PdCl2{R2P(E-CF[double bond, length as m-dash]CFCF3)}2] (R = Ph, iPr) and [Mo(CO)4{(CF3CF[double bond, length as m-dash]CF)2PCH2CH2P(CF[double bond, length as m-dash]CFCF3)2}] are reported.

Formation of diamonds and other carbon phases upon the destruction of palladium carbonyl clusters

Carbonyl clusters of general composition Pdx(CO)yClz, which are formed when solutions of chloropalladium(II)complexes are exposed to carbon monoxide, are shown to experience spontaneous destruction to yield palladium powder, CO2, CO, and carbon phases, in particular a diamond phase, due to the occurrence of the Boudoir reaction. The diamond is in the form of grains with sizes of ≤1 mm and diamond filaments with diameters of up to ten micrometers and lengths of up to 2 cm.

Immobilization of atmospheric nitrogen by lower palladium carbonyl complexes

It has been experimentally shown that the action of nitrogen onto hydrochloric acid solutions containing carbonylchloride complexes of palladium in lower oxidation states at room temperature and atmospheric pressure leads to its immobilization with the formation of ammonia. Some elements of the possible mechanism of the immobilization of nitrogen have been discussed.

The state of palladium and copper bromides in the PdBr2-CuBr2-THF-H2O system used in the conjugated process of cyclohexanecarboxylic acid production

The state of bromide complexes of palladium and copper in model solutions and under conditions of the conjugated catalytic synthesis of cyclohexanecarboxylic acid by the hydrocarboxylation of cyclohexene is studied by electron and infrared spectroscopy. It is found that during the conjugated process, copper exists in the form of copper(I) compounds, and palladium is present in the form of palladium(II) carbonyl complex.

Infrared Photodissociation Spectra of Mass‐Selected Homoleptic Dinuclear Palladium Carbonyl Cluster Cations in the Gas Phase

AbstractInfrared spectra of mass‐selected homoleptic dinuclear palladium carbonyl cluster cations Pd2(CO)n+ (n=5–8) are measured via infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The structures are established by comparison of the experimental spectra with simulated spectra derived from density functional calculations. The Pd2(CO)5+ cation is characterized to have two weakly semibridging CO groups with C2 symmetry. The Pd2(CO)6+ and Pd2(CO)7+ cations are determined to involve one weakly semibridging CO group. The Pd2(CO)8+ cation is a CO coordination saturated cluster, which is determined to have a D2d structure with all of the carbonyl groups terminally bonded. Bonding analysis indicates that these cluster cations each has a PdPd half bond. The PdPd distance increases with the number of CO ligands.

Mass-spectroscopy of polynuclear palladium carboxylate complexes as a key to new structures. Synthesis and X-Ray structure of Pd12(μ-CO)8(μ-NO2)8(μ-iPrCO2)8

Abstract Palladium NOx-containing polynuclear carboxylate complexes Pd4(μ-CO)2(μ-NO)(μ-iPrCO2)5 and Pd8(μ-CO)4(μ-NO2)4(μ-iPrCO2)8 were studied with MALDI-TOF mass-spectroscopic technique. The results confirm previous suggestion about Pd4 metal chains as building blocks for big palladium carbonyl carboxylate clusters. Also a new Pd3 bent metal chain observed in mass-spectra was demonstrated to serve a building block as well. Using the data the biggest palladium carboxylate cluster Pd12(μ-CO)8(μ-NO2)8(μ-iPrCO2)8 was synthesized and characterized by X-Ray analysis. Thus it was shown that mass-spectroscopic data for palladium carboxylates can be used for prediction of new structures of palladium clusters.

Palladium nitrosyl carboxylate clusters: Synthesis and reactivity. X-ray structures of Pd 4(μ-CO) 2(μ-NO)(μ-RCO 2) 5 (R = iPr, iBu)

New palladium nitrosyl carboxylate complexes Pd 8(CO) 4− m (NO) m (NO 2) 4(RCO 2) 8 ( m = 2, 4) were obtained by the treatment of palladium carbonyl carboxylates clusters cyclo-Pd n (μ-CO) n (μ-RCO 2) n ( n = 6) ( 1) with gaseous nitrogen monoxide. These complexes are the products of CO substitution in early described Pd 8(CO) 4(NO 2) 4(RCO 2) 8 clusters. By adding an excess of corresponding acid to reaction mixture Pd 4(CO) 2(NO)(RCO 2) 5 complexes were obtained, their structures were determined by X-ray diffraction analysis. These clusters are intermediate products of transformation of 6-nuclear initial clusters into various 8-nuclear complexes. This fact demonstrates that carboxylate ligands can be used as stabilizers for intermediate unstable polynuclear palladium compounds.

Heterocyclic carbenes of diverse flexibility: A theoretical insight

A systematic density functional investigation has been carried out on the structure, stability and reactivity of heterocyclic carbenes of diverse flexibility, i.e., carbenes with different modes of binding specially normal and remote mode of binding. Ligating properties of these carbenes have been assessed by virtue of their HOMO energies and verified further by inspection of the symmetric CO frequencies of their respective palladium carbonyl complexes. All the remote carbenes were found to have higher σ-donating abilities compared to their normal analogs. N-heterocyclic carbenes 1 and 5 are found to be electrophilic in nature while the remote carbene 3 and P-heterocyclic carbene 6 are found to be nucleophilic. Quantum theory of atoms in molecules (QTAIM) reveals significant covalent character in the C carbene–Pd bonds.

ChemInform Abstract: Palladium(I) Carbonyl Cation Catalyzed Carbonylation of Olefins and Alcohols in Concentrated Sulfuric Acid.

A new palladium catalyst was found to exhibit high catalytic activity for carbonylation of olefins and alcohols. cyclo-Bis(μ-carbonyl)dipalladium(I) cation (1) with bridging CO ligands is formed by reductive carbonylation of palladium sulfate, PdSO4, in concentrated H2SO4. When an olefin or alcohol is added, complex 1 changes to a new complex (2) with terminal CO ligands, and tertiary carboxylic acids are obtained in high yields at room temperature and atmospheric pressure of CO. IR and 13C NMR studies suggest that complex 2 may be tentatively formulated to be [Pd2(CO)2]2+, in which the terminal CO ligands are chemically equivalent. Complex 1 is a catalyst precursor, and complex 2 functions as an active species for the carbonylation of olefins and alcohols. The catalytic behavior of the palladium carbonyl catalyst supports the recently proposed reaction mechanism involving an olefin−metal−CO complex as an intermediate for the catalytic carbonylation of olefins and alcohols in strongly acidic solution.

Synthesis and some properties of heteronuclear platinum and palladium carbonyl clusters

Heteronuclear clusters of general formula [PtxPdy(CO) z] were synthesized by reaction of CO with PtCl4 + PdCl2 solutions in 95% ethanol at room temperature and atmospheric pressure. The products isolated were analyzed by IR spectroscopy, thermogravimetry, and X-ray powder diffraction.

Mechanistic Study of the Palladium–Phenanthroline Catalyzed Carbonylation of Nitroarenes and Amines: Palladium–Carbonyl Intermediates and Bifunctional Effects

Palladium-phenanthroline complexes catalyze both the nitroarene carbonylation reaction and the amine oxidative carbonylation reaction to give, depending on the conditions, carbamates and ureas. There is evidence that the key step in both processes is the amine carbonylation. Here, we show that when the reaction is run in methanol key intermediate compounds have the general formula [Pd(RPhen)(COOMe)(2)] (1) (RPhen = 1,10-phenanthroline or one of its substituted derivatives). The kinetics of the reaction of 1 with toluidine in the presence of a carboxylic or phosphorus acid is first-order with respect to complex, acid, and toluidine. A CO atmosphere is also required for the reaction to proceed. Acid dimerization was shown not to be influential under the concentration conditions examined, but reaction between the acid and toluidine is not negligible and a correction has to be applied. Diphenylphosphinic acid is more effective than any carboxylic acid in promoting this reaction, as also observed under catalytic conditions. A series of equilibria and an irreversible acid-assisted proton transfer explain the observed data. Formation of an adduct between complexes of the kind 1 and CO was spectroscopically observed when RPhen = 2,9-Me(2)Phen. Several analogous complexes were also spectroscopically characterized and the X-ray structure of [Pd(2,9-Me(2)Phen)Cl(2)(CO)] was solved. This shows an asymmetric coordination of the nitrogen ligand. Kinetic measurements were also conducted under catalytic conditions. An Eyring plot shows that the effect of the acidic promoter is to decrease the DeltaS(double dagger) value, whereas no positive effect is observed on DeltaH(double dagger). A temperature-dependent correction for the reaction between the acid and aniline and phenanthroline present under the reaction conditions has to be applied. Comparison of the results obtained under stoichiometric and catalytic conditions strongly supports the view that 1 is involved even in the latter and that the acid is acting as a bifunctional promoter.

Palladium(II) carboxylates and palladium(I) carbonyl carboxylate complexes as catalysts for olefin cyclopropanation with ethyl diazoacetate

Palladium(I) carbonyl carboxylate complexes [Pd(mu-CO)(mu-RCO2)](n) (R = Me, n = 4; R = CMe(3), n = 6) and the corresponding palladium(II) carboxylates (acetate and pivalate) catalyze the cyclopropanation of olefins with ethyl diazoacetate. The performance of these catalysts is similar in terms of selectivity and cyclopropane yields, regardless of the oxidation state of the metal center. However the rates of the cyclopropanation reactions are significantly higher for the acetate based catalysts than for the pivalate derivatives, which suggests that the main catalytic species are carboxylate containing palladium complexes. Kinetic measurements show that reaction rates are independent of the olefin concentration when these are 1-hexene or styrene, but norbornene exerts an inhibitory effect. In spite of this, competition experiments indicate that the cyclopropanation of styrene is 2.2 times as favorable as that of 1-hexene for any of the four catalysts. These observations indicate that while the rate-determining formation of the intermediate palladium carbenoid species is controlled by the catalyst structure, this is followed by a rapid and less specific cyclopropanation step that is not affected by the nature of the carboxylate groups present in the catalyst. An independent test using a 1:1 benzene/cyclohexane mixture of solvents showed that the transfer of ethoxycarbonylcarbene (:C(CO2Et)H) to these molecules is unselective (relative rate of benzene/cyclohexane functionalization approximately 1.8, independent of the catalyst). This result can be interpreted as an indication of the involvement of free ethoxycarbonylcarbene in the carbene transfer step.

Interaction of polynuclear palladium (I) carbonyl carboxylates with gaseous NO: X-ray structure of eight-nuclear clusters Pd8(μ-CO)4(μ-OOCR)4[μ-N(O)O–

The reaction of palladium carbonyl carboxylates Pd 6 (CO) 6 (RCOO) 6 with gaseous nitrogen monoxide was investigated. These clusters were found to promote the NO disproportionation into N 2 and NO 2 under mild conditions. The reaction is accompanied with the oxidation of coordinated carbon monoxide. These processes result in unusual eight-nuclear palladium carboxylate clusters Pd 8 (CO) 4 (NO 2 ) 4 (RCOO) 8 .

Nitrogen monoxide as an oxidant in reactions promoted by palladium(i) carbonyl carboxylate clusters

The reaction of the palladium(i) cluster Pd6(CO)6(OCOCMe3)6 having a cyclic metal core with gaseous nitrogen monoxide was studied by electronic absorption spectroscopy, IR spectroscopy, and GLC. In the system studied NO acts as an oxidant for both coordinated CO (oxidation to CO2) and NO itself, being reduced predominantly to N2. The product of nitrogen monoxide oxidation (NO2) was found in coordinated state in the new cluster Pd8(μ-CO)4(μ-NO2)4(μ-OCOCMe3)8. The cluster has an unusual structure: two tetranuclear metal chains Pd(μ-OCOCMe3)2Pd(μ-CO)2Pd(μ-OCOCMe3)2Pd are linked through four equivalent bridges -N(=O)-O- in such a way that a bulky cavity is formed.