Theoretical investigation into the mechanism of reductive elimination from bimetallic palladium complexes

Reductive elimination of C-Cl and C-C bonds from binuclear organopalladium complexes containing Pd-Pd bonds with overall formal oxidation state +III are explored by density functional theory for dichloromethane and acetonitrile solvent environments. An X-ray crystallographically authenticated neutral complex, [(L-C,N)ClPd(μ-O(2)CMe)](2) (L = benzo[h]quinolinyl) (I), is examined for C-Cl coupling, and the proposed cation, [(L-C,N)PhPd(1)(μ-O(2)CMe)(2)Pd(2)(L-C,N)](+) (II), examined for C-C coupling together with (L-C,N)PhPd(1)(μ-O(2)CMe)(2)Pd(2)Cl(L-C,N) (III) as a neutral analogue of II. In both polar and nonpolar solvents, reaction from III via chloride dissociation from Pd(2) to form II is predicted to be favored. Cation II undergoes Ph-C coupling at Pd(1) with concomitant Pd(1)-Pd(2) lengthening and shortening of the Pd(1)-O bond trans to the carbon atom of L; natural bond orbital analysis indicates that reductive coupling from II involves depopulation of the d(x(2)-y(2)) orbital of Pd(1) and population of the d(z(2)) orbitals of Pd(1) and Pd(2) as the Pd-Pd bond lengthens. Calculations for the symmetrical dichloro complex I indicate that a similar dissociative pathway for C-Cl coupling is competitive with a direct (nondissociative) pathway in acetonitrile, but the direct pathway is favored in dichloromethane. In contrast to the dissociative mechanism, direct coupling for I involves population of the d(x(2)-y(2)) orbital of Pd(1) with Pd(1)-O(1) lengthening, significantly less population occurs for the d(z(2)) orbital of Pd(1) than for the dissociative pathway, and d(z(2)) at Pd(2) is only marginally populated resulting in an intermediate that is formally a Pd(1)(I)-Pd(2)(III) species, (L-Cl-N,Cl)Pd(1)(μ-O(2)CMe)Pd(2)Cl(O(2)CMe)(L-C,N) that releases chloride from Pd(2) with loss of Pd(I)-Pd(III) bonding to form a Pd(II) species. A similar process is formulated for the less competitive direct pathway for C-C coupling from III, in this case involving decreased population of the d(z(2)) orbital of Pd(2) and strengthening of the Pd(I)-Pd(III) interaction in the analogous intermediate with η(2)-coordination at Pd(1) by L-Ph-N, C(1)-C(2).     

Tetrapalladium complex with bridging germylene ligands. Structural change of the planar Pd4Ge3 core

A complex with a planar hexagonal Pd(4)Ge(3) core, [Pd{Pd(dmpe)}(3)(μ(3)-GePh(2))(3)], was synthesized and characterized by X-ray and NMR measurements as well as by DFT calculations. 4-tert-Butylbenzenethiol converted the Pd(4) complex into a hexapalladium complex, [{Pd(3)(μ-GePh(2))(2)(μ-H)(μ(3)-GePh(2)(SC(6)H(4)(t)Bu-4))}(2)(μ-dmpe)], composed of two Pd(3)Ge(3) units bridged by a dmpe ligand. The addition of CuI or AgI to the Pd(4) complex yielded [Pd(μ-MI){Pd(dmpe)}(3)(μ(3)-GePh(2))(3) ] (M = Cu, Ag), in which Cu or Ag bridges a Pd-Pd bond of the Pd(4)Ge(3) core. The CuI adducts in solution undergo a pivot motion of the CuI on the surface of the Pd(4)Ge(3) plane on the NMR time scale.     

Structure elucidation of the unprecedented asymmetric bis-chelate complex [Pd(1,3-bis(di(o-methoxy-m-methylphenyl)phosphino)propane)2]2+ in the solid state and in solution

Complexes of the type [Pd(ligand)(2)](anion)(2) were prepared with a series of bidentate di(o-methoxyphenyl)phosphine ligands with increasing steric bulk on the meta position of the phenyl groups: m-H (L1); m-MeO (L2); and m-Me (L3). The solid-state structure of [Pd(L2)(2)](OTs)(2) revealed that the two ligands are symmetrically coordinated to Pd(2+). In the solid state structure of [Pd(L3)(2)](OTs)(2) however, the two ligands are unsymmetrically coordinated to Pd(2+), yielding an unprecedented conformation of this bis-chelate P(4)Pd(2+) complex. (1)H-(1)H-COSY and NOESY analysis and a (31)P-NMR simulation showed that the asymmetric structure of [Pd(L3)(2)](OTs)(2) is retained in solution.     

Redox non-innocence of thioether crowns: elucidation of the electronic structure of the mononuclear Pd(III) complexes [Pd([9]aneS3)2]3+ and [Pd([18]aneS6)]3+

The Pd(II) complexes [Pd([9]aneS(3))(2)](PF(6))(2)·2MeCN (1) ([9]aneS(3) = 1,4,7-trithiacyclononane) and [Pd([18]aneS(6))](PF(6))(2) (2) ([18]aneS(6) = 1,4,7,10,13,16-hexathiacyclooctadecane) can be oxidized electrochemically or chemically oxidized with 70% HClO(4) to [Pd([9]aneS(3))(2)](3+) and [Pd([18]aneS(6))](3+), respectively. These centers have been characterized by single crystal X-ray diffraction, and by UV/vis and multifrequency electron paramagnetic resonance (EPR) spectroscopies. The single crystal X-ray structures of [Pd(III)([9]aneS(3))(2)](ClO(4))(6)·(H(3)O)(3)·(H(2)O)(4) (3) at 150 K and [Pd([18]aneS(6))](ClO(4))(6)·(H(5)O(2))(3) (4) at 90 K reveal distorted octahedral geometries with Pd-S distances of 2.3695(8), 2.3692(8), 2.5356(9) and 2.3490(6), 2.3454(5), 2.5474(6) ?, respectively, consistent with Jahn-Teller distortion at a low-spin d(7) Pd(III) center. The Pd(II) compound [Pd([9]aneS(3))(2)](PF(6))(2) shows a one-electron oxidation process in MeCN (0.2 M NBu(4)PF(6), 293 K) at E(1/2) = +0.57 V vs. Fc(+)/Fc assigned to a formal Pd(III)/Pd(II) couple. Multifrequency (Q-, X-, S-, and L-band) EPR spectroscopic analysis of [Pd([9]aneS(3))(2)](3+) and [Pd([18]aneS(6))](3+) gives g(iso) = 2.024, |A(iso(Pd))| = 18.9 × 10(-4) cm(-1); g(xx) = 2.046, g(yy) = 2.041, g(zz) = 2.004;?|A(xx(Pd))| = 24 × 10(-4) cm(-1), |A(yy(Pd))| = 22 × 10(-4) cm(-1), |A(zz(Pd))| = 14 × 10(-4) cm(-1), |a(xx(H))| = 4 × 10(-4) cm(-1), |a(yy(H))| = 5 × 10(-4) cm(-1), |a(zz(H))| = 5.5 × 10(-4) cm(-1) for [Pd([9]aneS(3))(2)](3+), and g(iso) = 2.015, |A(iso(Pd))| = 18.8× 10(-4) cm(-1); g(xx) = 2.048 g(yy) = 2.036, g(zz) = 1.998; |a(xx(H))| = 5, |a(yy(H))| = 5, |a(zz(H))| = 6 × 10(-4) cm(-1); |A(xx(Pd))| = 23× 10(-4) cm(-1), |A(yy(Pd))| = 22 × 10(-4) cm(-1), |A(zz(Pd))| = 4 × 10(-4) cm(-1) for [Pd([18]aneS(6))](3+). Both [Pd([9]aneS(3))(2)](3+) and [Pd([18]aneS(6))](3+) exhibit five-line superhyperfine splitting in the g(zz) region in their frozen solution EPR spectra. Double resonance spectroscopic measurements, supported by density functional theory (DFT) calculations, permit assignment of this superhyperfine to through-bond coupling involving four (1)H centers of the macrocyclic ring. Analysis of the spin Hamiltonian parameters for the singly occupied molecular orbital (SOMO) in these complexes gives about 20.4% and 25% Pd character in [Pd([9]aneS(3))(2)](3+) and [Pd([18]aneS(6))](3+), respectively, consistent with the compositions calculated from scalar relativistic DFT calculations.     

Thermal and electrochemically assisted Pd-Cl bond cleavage in the d9-d9 Pd2dppm2Cl2 complex by Pd3 dppm3COn+ clusters (n = 2, 1, 0)

A new aspect of reactivity of the cluster [Pd3(dppm)3(micro3-CO)]n+, ([Pd3]n+, n = 2, 1, 0) with the low-valent metal-metal-bonded Pd2(dppm)2Cl2 dimer (Pd2Cl2) was observed using electrochemical techniques. The direct reaction between [Pd3]2+ and Pd2Cl2 in THF at room temperature leads to the known [Pd3(dppm)3(micro3-CO)(Cl)]+ ([Pd3(Cl)]+) adduct and the monocationic species Pd2(dppm)2Cl+ (very likely as Pd2(dppm)2(Cl)(THF)+, [Pd2Cl]+) as unambiguously demonstrated by UV-vis and 31P NMR spectroscopy. In this case, [Pd3]2+ acts as a strong Lewis acid toward the labile Cl- ion, which weakly dissociates from Pd2Cl2 (i.e., dissociative mechanism). Host-guest interactions between [Pd3]2+ and Pd2Cl2 seem unlikely on the basis of computer modeling because of the strong screening of the Pd-Cl fragment by the Ph-dppm groups in Pd2Cl2. The electrogenerated clusters [Pd3]+ and [Pd3]0 also react with Pd2Cl2 to unexpectedly form the same oxidized adduct, [Pd3(Cl)]+, despite the known very low affinity of [Pd3]+ and [Pd3]0 toward Cl- ions. The reduced biproduct in this case is the highly reactive zerovalent species "Pd2(dppm)2" or "Pd(dppm)" as demonstrated by quenching with CDCl3 (forming the well-known complex Pd(dppm)Cl2) or in presence of dppm (forming the known Pd2(dppm)3 d10-d10 dimer). To bring these halide-electron exchange reactions to completion for [Pd3]+ and [Pd3]0, 0.5 and 1.0 equiv of Pd2Cl2 are necessary, respectively, accounting perfectly for the number of exchanged electrons. The presence of a partial dissociation of Pd2Cl2 into the Cl- ion and the monocation [Pd2Cl]+, which is easier to reduce than Pd2Cl2, is suggested to explain the overall electrochemical results. It is possible to regulate the nature of the species formed from Pd2Cl2 by changing the state of charge of the title cluster.     

Lewis acid-base interactions between metal atoms and their applications for the synthesis of bimetallic cluster complexes

A series of new palladium-ruthenium cluster complexes have been prepared by adding Pd(PBu(t)(3)) fragments to the ruthenium-ruthenium bonds of ruthenium carbonyl complexes. Reaction of Pd(PBu(t)(3))(2) with Ru(3)(CO)(12) yielded the tripalladium adduct Ru(3)(CO)(12)[Pd(PBu(t)(3))](3) 1. Compound 1 contains three Pd(PBu(t)(3)) groups symmetrically disposed with each one acting as a bridge across one Ru-Ru bond of the former Ru(3)(CO)(12) molecule. Reaction of Pd(PBu(t)(3))(2) with Ru(6)(CO)(17)(C) yielded the dipalladium adduct Ru(6)(CO)(17)(C)[Pd(PBu(t)(3))](2) 2. Compound 2 exists as two isomers in the solid state. One isomer has Pd(PBu(t)(3)) groups bridging two edges of the Ru(6) octahedron. The other isomer has a Pd(PBu(t)(3)) group bridging one edge of the Ru(6) octahedron, and the other is a triple bridge. The reaction of Pd(PBu(t)(3))(2) with Ru(CO)(5) yielded the dipalladium-diruthenium complex Ru(2)(CO)(9)[Pd(PBu(t)(3))](2) 3, a dipalladium adduct of the unstable molecule Ru(2)(CO)(9).     

Exploring the metal coordination properties of the pyrimidine part of purine nucleobases: isomerization reactions in heteronuclear Pt(II)/Pd(II) of 9-methyladenine

The synthesis and characterization of three heteronuclear Pt(2)Pd(2) (4, 5) and PtPd(2) (6) complexes of the model nucleobase 9-methyladenine (9-MeA) is reported. The compounds were prepared by reacting [Pt(NH(3))(3)(9-MeA-N7)](ClO(4))(2) (1) with [Pd(en)(H(2)O)(2)](ClO(4))(2) at different ratios r between Pt and Pd, with the goal to probe Pd(II) binding to any of the three available nitrogen atoms, N1, N3, N6 or combinations thereof. Pd(II) coordination occurs at N1 and at the deprotonated N6 positions, yet not at N3. 4 and 5 are isomers of [{(en)Pd}(2){N1,N6-9-MeA(-)-N7)Pt(NH(3))(3)}(2)](ClO(4))(6)·nH(2)O, with a head-head orientation of the two bridging 9-MeA(-) ligands in 4 and a head-tail orientation in 5. 6 is [{(en)Pd}(2)(OH)(N1,N6-9MeA(-)-N7)Pt(NH(3))(3)](ClO(4))(4)·4H(2)O, hence a condensation product between [Pt(NH(3))(3)(9-MeA-N7)](2+) and a μ-OH bridged dinuclear (en)Pd-OH-Pd(en) unit, which connects the N1 and N6 positions of 9-MeA(-) in an intramolecular fashion. 4 and 5, which slowly interconvert in aqueous solution, display distinct structural differences such as significantly different intramolecular Pd···Pd contacts (3.124 0(16) ? in 4; 2.986 6(14) ? in 5), among others. Binding of (en)Pd(II) to the exocyclic N6 atom in 4 and 5 is accompanied by a large movement of Pd(II) out of the 9-MeA(-) plane and a trend to a further shortening of the C6-N6 bond as compared to free 9-MeA. The packing patterns of 4 and 5 reveal substantial anion-π interactions.     

Using ligand bite angles to control the hydricity of palladium diphosphine complexes

A series of [Pd(diphosphine)(2)](BF(4))(2) and Pd(diphosphine)(2) complexes have been prepared for which the natural bite angle of the diphosphine ligand varies from 78 degrees to 111 degrees. Structural studies have been completed for 7 of the 10 new complexes described. These structural studies indicate that the dihedral angle between the two planes formed by the two phosphorus atoms of the diphosphine ligands and palladium increases by over 50 degrees as the natural bite angle increases for the [Pd(diphosphine)(2)](BF(4))(2) complexes. The dihedral angle for the Pd(diphosphine)(2) complexes varies less than 10 degrees for the same range of natural bite angles. Equilibrium reactions of the Pd(diphosphine)(2) complexes with protonated bases to form the corresponding [HPd(diphosphine)(2)](+) complexes were used to determine the pK(a) values of the corresponding hydrides. Cyclic voltammetry studies of the [Pd(diphosphine)(2)](BF(4))(2) complexes were used to determine the half-wave potentials of the Pd(II/I) and Pd(I/0) couples. Thermochemical cycles, half-wave potentials, and measured pK(a) values were used to determine both the homolytic ([HPd(diphosphine)(2)](+) --> [Pd(diphosphine)(2)](+) + H*) and the heterolytic ([HPd(diphosphine)(2)](+) --> [Pd(diphosphine)(2)](2+) + H(-)) bond-dissociation free energies, Delta G(H*)* and Delta G(H-)*, respectively. Linear free-energy relationships are observed between pK(a) and the Pd(I/0) couple and between Delta G(H-)* and the Pd(II/I) couple. The measured values for Delta G(H*)* were all 57 kcal/mol, whereas the values of Delta G(H-)* ranged from 43 kcal/mol for [HPd(depe)(2)](+) (where depe is bis(diethylphosphino)ethane) to 70 kcal/mol for [HPd(EtXantphos)(2)](+) (where EtXantphos is 9,9-dimethyl-4,5-bis(diethylphosphino)xanthene). It is estimated that the natural bite angle of the ligand contributes approximately 20 kcal/mol to the observed difference of 27 kcal/mol for Delta G(H-)*.     

Multifaceted palladium catalysts towards the tandem diboration-arylation reactions of alkenes

Novel Pd(2) (6+) compounds have been synthesized in high yield. These compounds and their Pd(2) (4+) counterparts as synthetic precursors mediate the diboration of vinylarenes and aliphatic 1-alkenes, and under mild and basic reaction conditions they produce a variety of 1,2-diboronate esters with excellent conversions and chemoselectivities. The presence of bis(catecholato)diboron (B(2)cat(2)) favours the reduction of Pd(III) to Pd(II), while the catalytic precursor of Pd(II) is transformed into Pd(0)-nanoparticles. An "in situ" catalytic tandem reaction has been designed to transform the diboronate intermediates into the monoarylated product, which after oxidative workup, provides the carbohydroxylated adduct. Eventually, the same catalyst performs both sequences with total conversion from the alkene.     

Providing support in favor of the existence of a Pd(II)/Pd(IV) catalytic cycle in a Heck-type reaction

The complex [Pd(O,N,C-L)(OAc)], in which L is a monoanionic pincer ligand derived from 2,6-diacetylpyridine, reacts with 2-iodobenzoic acid at room temperature to afford the very stable pair of Pd(IV) complexes (OC-6-54)- and (OC-6-26)-[Pd(O,N,C-L)(O,C-C(6)H(4)CO(2)-2)I] (1.5:1 molar ratio, at -55?°C). These complexes and the Pd(II) species [Pd(O,N,C-L)(OX)] and [Pd(O,N,C-L')(NCMe)]ClO(4), (X = MeC(O) or ClO(3), L' = another monoanionic pincer ligand derived from 2,6-diacetylpyridine), are precatalysts for the arylation of CH(2)=CHR (R = CO(2)Me, CO(2)Et, Ph) using IC(6)H(4)CO(2)H-2 and AgClO(4). These catalytic reactions have been studied and a tentative mechanism is proposed. The presence of two Pd(IV) complexes was detected by ESI(+)-MS during the catalytic process. All the data obtained strongly support a Pd(II)/Pd(IV) catalytic cycle.     

Factors determining the chemoselectivity of phosphorus-modified palladium catalysts in the hydrogenation of chloronitrobenzenes

The precursor nature effect on the state of the Pd–P surface layer in palladium catalysts and on their properties in the liquid-phase hydrogenation of chloronitrobenzenes under mild conditions has been investigated. A general feature of the Pd–P-containing nanoparticles obtained from different precursors and white phosphorus at P/Pd = 0.3 (PdCl₂ precursor) and 0.7 (Pd(acac)₂ precursor) is that their surface contains palladium in phosphide form (BE(Pd3d _5/2) = 336.2 eV and BE(Р2р) = 128.9 eV) and Pd(0) clusters (BE(Pd3d_5/2) = 335.7 eV). Factors having an effect on the chemoselectivity of the palladium catalysts in chloronitrobenzenes hydrogenation are considered, including the formation of small palladium clusters responsible for hydrogenation under mild conditions.     

Pd6簇与H2分子相互作用的密度泛函理论研究

通过相对论有效核势密度泛函理论计算,优化了Pd6(H)2和Pd6(H)4等簇的平衡几何结构,预测了氢分子在Pd6簇表面上的吸附行为与活化解离性质.计算结果表明,单态的Pd6簇可以活化两个氢分子;第一个H2和第二个H2吸附解离过程速率决定步骤的能垒分别是66.4和24.5kJ/mol、在形成的分子氢配合物Pd6(H2)和Pd（H)2H2中,H2主要作为给电子配体.在最稳定的二氢簇合物Pd6(H)2中,H倾向与3个Pd相互作用,形成面位氢的多核成键吸附方式.     

Impact of Pd-mordenite pretreatment on the heterogeneity of Heck catalysis

In Heck reactions with tributylamine as the base and in toluene, Pd(NH3)4(2+)-mordenite (0.4 wt% Pd) and Pd0-mordenite (0.4 and 4 wt% Pd) are not only active and selective, but also truly heterogeneous catalysts, while oxidized PdII species in an all-oxygen environment, i.e. ionic Pd2+ or PdO, are prone to leaching.     

Charged molecular alloys: synthesis and characterization of the binary anions Pd(7)As(16)(4-) and Pd(2)As(14)(4-)

Pd(PCy(3))(2) (Cy = cyclohexyl) reacts with As(7)(3-) in en/tol solvent mixtures to give Pd(2)As(14)(4-) (2) and Pd(7)As(16)(4-) (4) as the [K(2,2,2-crypt)](+) salts. The anions were characterized by EDX, ESI-MS, and single-crystal X-ray diffraction. Anion 2 formally contains two norbornadiene-like As(7)(5-) groups bound to square-planar Pd(III) centers linked by a Pd-Pd bond (d(Pd)(-)(Pd) = 2.7144(6) A). Anion 4 has a highly distorted capped trigonal prismatic Pd(7) core stabilized by 2 As(5)(1-), 2 As(2)(2-), and 2 As(3-) anions. The 6 Pd(I) ions are in distorted 5-coordinate environments whereas the lone Pd(II) ion is square planar. Complexes 2 and 4 are rare examples of organic-free, homoleptic transition metal anions containing group 15 elements, and they represent an emerging class of charged "molecular alloys".     

On the roles of solid-bound ligand scavengers in the removal of palladium residues and in the distinction between homogeneous and heterogeneous catalysis

We have studied the roles and behavior of typical resin- and silica-bound thiol scavengers in the removal of palladium (Pd) residues and in the determination of the true catalytic species in the Heck coupling of bromobenzene and styrene. The results of Pd scavenging and catalyst poisoning by elemental analysis (EA) and transmission electron microscopy (TEM) indicate that silica-bound thiols have an advantage over resin-bound thiols in residual Pd removal from a Heck reaction solution and that all of these scavengers poison effectively the catalytic species but hardly scavenge Pd clusters, even as small as 1 nm from solution presumably because of the steric barrier. Because of a smaller proportion of soluble Pd clusters, using a molecular Pd precatalyst results in a much higher Pd scavenging efficiency than using a supported Pd particle precatalyst. With the aid of catalyst poisoning by the scavengers, filtration testing and TEM studies further illustrate that Pd clusters are inactive for the Heck reaction over Pd(0)/SiO(2), with molecular Pd(0) being solely active. Studies through EA and thermogravimetric analysis suggest that the bound thiols are leached from the scavengers to a different extent at reaction temperatures of 90-135 °C, probably owing to base-catalyzed decomposition or based-promoted dissociation of functional groups from the surfaces, leading to interaction between leached thiols and a solid Pd precatalyst. Meanwhile, the effect of solid-bound thiol binding to soluble Pd on the efficiency of Pd scavenging and the impact of a scavenger on the Pd leaching from supported Pd particles are discussed.     

Pd（OAc）2／FePc催化环己烯氧化合成环己酮的研究

考察了几种Ｆｅ－大环配合物与Ｐｄ（ＯＡｃ）２组成的双组分催化体系，在乙腈酸性水溶液中环己烯经合成环己酮的催化活性，实验结果表明，其中以酞菁失（ＦｅＰｃ）与Ｐｄ（ＯＡｃ）２组成的催化体系活性最高，而ＦｅＴＰＰＣｌ与Ｐｄ（ＯＡｃ）２催化体系，虽然催化活性较高，但催化剂的稳定性较低，各种因素对Ｐｄ（ＯＡｃ）２／ＦｅＰｃ催化活催化影响的研究结果指出，在无水和酸存在的非水溶液中，Ｐｄ（ＯＡｃ）２／ＦｅＰｃ对     

Autocatalytic oxidative addition of PhBr to Pd(PtBu3)2 via Pd(PtBu3)2(H)(Br)

We report that oxidative addition of bromobenzene to Pd(PtBu3)2 occurs by an unusual autocatalytic mechanism. Studies on the effect of various additives showed that the degree of rate acceleration followed the trend: (PtBu3)Pd(Ph)(Br) approximately (HPtBu3)Br < [(PtBu3)Pd(mu-Br)]2 < (PtBu3)2Pd(H)(Br). Studies on the reactions of Pd(PtBu3)2 in the presence of (PtBu3)2Pd(H)(Br) showed that the concentration of (PtBu3)2Pd(H)(Br) decreased only after the Pd(0) complex had been consumed. These data indicated that the catalyst in this process is (PtBu3)2Pd(H)(Br). Thermal decomposition of the three-coordinate oxidative addition product (PtBu3)Pd(Ar)(Br) during the reaction of Pd(PtBu3)2 and bromoarenes ultimately leads to formation of (PtBu3)2Pd(H)(Br). Parallel reactions of bromobenzene with (PtBu3)2Pd(H)(Br) and Pd(PtBu3)2 showed that the bromoarenes reacted considerably faster with the Pd(II) species than with the Pd(0) species. We therefore propose a catalytic cycle for oxidative addition in which PBut3.HBr reacts with the Pd(0) species to form (PtBu3)2Pd(H)(Br), and (PtBu3)2Pd(H)(Br) reacts with the bromoarene, possibly though the anionic species [HPtBu3+][(PtBu3)Pd(Br)-], to form [Pd(PtBu3)(Ar)(Br)].     

Studies of the oxidation of palladium complexes by the advanced oxidation process Pretreatment of model catalysts for precious metal analysis

The advanced oxidation process (AOP) for the pretreatment of model palladium catalysts has been studied. Most standard metal analysis techniques are for metal ions free of organic ligands. Spent palladium catalysts contain organic ligands that need to be removed prior to analysis. AOP uses a combination of hydrogen peroxide and UV light to generate radicals that decompose such ligands, freeing up metals for further analysis. Palladium acetate Pd(OAc)₂, palladium acetylacetonate Pd(acac)₂, and tris(dibenzylideneacetone)dipalladium (Pd₂(dba)₃) were chosen as model precious metal catalysts for investigation. AOP was found to decompose ligands in Pd(OAc)₂, Pd(acac)₂ and give accurate Pd(II) quantification, while ligand decomposition and oxidation of Pd(0) to Pd(II) were demonstrated in treatments involving Pd₂(dba)₃. The effects of solubility of the palladium complexes, continuous addition of H₂O₂ during AOP treatments, sample pH, concentration of H₂O₂, and length of UV irradiation are reported.     

Extraordinarily high activity in the hydrodesulfurization of 4,6-dimethyldibenzothiophene over Pd supported on mesoporous zeolite Y

Design and preparation of highly active hydrodesulfurization (HDS) catalysts is very important for the removal of air pollution. Herein, we report an extraordinarily active HDS catalyst, which is synthesized by loading of Pd on mesoporous zeolite Y (Pd/HY-M). The mesoporous zeolite Y is successfully synthesized using a water glass containing N,N-dimethyl-N-octadecyl-N-(3-triethoxysilylpropyl) ammonium [(C(2)H(5)O)(3)SiC(3)H(6)N(CH(3))(2)C(18)H(37)](+) cation as a mesoscale template. Compared with mesoporous Beta and ZSM-5 supported Pd catalysts (80.0% and 73.4% for Pd/HBeta-M and Pd/HZSM-5-M, respectively) as well as commercial catalyst of γ-Al(2)O(3) supported Pd catalyst (31.4%), Pd/HY-M catalyst exhibited very high activity in HDS of 4,6-dimethyldibenzothiophene (4,6-DM-DBT, 97.3%). The higher activity of Pd/HY-M than that of Pd/HBeta-M and Pd/HZSM-5-M is assigned to the larger micropore size of zeolite Y compared to that of Beta and ZSM-5. Theoretical simulation and adsorption experimental data show that 4,6-DM-DBT has difficulty entering the micropores of ZSM-5 and Beta zeolites, but the micropores of Y zeolite are accessible.