Mol Pd Research Articles

The Effect of Weakly Coordinating Solvent and Counter Anion on Diphosphine‐Palladium(II) Catalytic Reactivity for Copolymerization of 1‐Butene with Carbon Monoxide in Aqueous Media

AbstractWater soluble bis(acetonitrile) diphospalladium (II) complexes cis‐[Pd(L1–L5)(NCCH3)2][BF4]2 (C1–C5) were obtained by the reaction [Pd(NCCH3)4][BF4]2 with diphosphines ligands L1–L5 (CH2(CH2PR2)2: where R=(CH2)nP(O)(OEt)2, n=2–4, n=6 and n=8)) in dichloromethane–acetonitrile. The isolated complexes were characterized by elemental analysis, FTIR, 1H‐ and 31P‐NMR spectroscopy. The complexes were applied as catalysts for the copolymerization of 1‐butene with carbon monoxide in aqueous media. The present work emphasized on the effect of weakly coordinated solvent and counterion on the catalytic behavior of cis‐[Pd(L1–L5)(NCCH3)2][BF4]2 complexes compared to previously prepared cis‐[ Pd(L1–L5)(OAc)2] (A1–A5). The exchange of π‐bonding NCCH3 ligand with π‐bonding CO and alkene was more favored than the exchange of σ‐bonding OAc− as reflected by the much higher catalytic activity (TON) of the former compared to the latter. In order to compare the catalytic efficiency of water soluble complexes with the performance of a standard, the water insoluble complex, cis‐[Pd(CH2(CH2P(CH2CH3)2)2(NCCH3)2][BF4]2, C6, was prepared and incorporated in the investigations. The isolated alternating 1‐butene/CO copolymer exhibits glass transition temperature of Tg=−3–−15 °C, which is in the range desirable for latex emulsion application. The solid content is up to 21 % with high molecular weight (Mw=4×104 g mol−1) and narrow polydispersities (Mw/Mn=2–3). The C5 complex was found to be fourteen times more active in aqueous polymerization medium (6369 mol substr. mol Pd−1 h−1) than C6 complex in nonaqueous medium (441 mol substr. mol Pd−1 h−1).

Highly dispersed Pd-based pseudo-single atoms in zeolites for hydrogen generation and pollutant disposal.

Atomically dispersed metal catalysts with excellent activity and stability are highly desired in heterogeneous catalysis. Herein, we synthesized zeolite-encaged Pd-based pseudo-single atoms via a facile and energy-efficient ligand-protected direct H2 reduction method. Cs-corrected scanning transmission electron microscopy, extended X-ray absorption, and pair distribution function measurements reveal that the metal species are close to atomic-level dispersion and completely confined within the intersectional channels of silicalite-1 (S-1) zeolite with the MFI framework. The Pd@S-1-H exhibits excellent activity and stability in methane combustion reactions with a complete combustion temperature of 390 °C, and no deactivation is observed even after 100 h on stream. The optimized bimetallic 0.8Pd0.2Ni(OH)2@S-1-H catalyst exhibits an excellent H2 generation rate from FA decomposition without any additives, affording a superhigh turnover frequency up to 9308 h-1 at 333 K, which represents the top activity among all of the best heterogeneous catalysts under similar conditions. Significantly, zeolite-encaged metal catalysts are first used for Cr(vi) reduction coupled with formic acid (FA) dehydrogenation and show a superhigh turnover number of 2980 mol(Cr2O72-) mol(Pd)-1 at 323 K, surpassing all of the previously reported catalysts. This work demonstrates that zeolite-encaged pseudo-single atom catalysts are promising in efficient hydrogen storage and pollutant disposal applications.

Magnetically isolable Pd(0) nanoparticles supported on surface functionalized Fe3O4 for hydrogen generation via ammonia borane hydrolysis

AbstractPd(0) nanoparticles supported on surface functionalized magnetite (Fe3O4/SiO2‐NH2/HB@Pd) were prepared as catalyst for hydrolysis of ammonia borane (AB). The obtained magnetic nanocomposite material was seperated from the reaction media through a permanent magnet and characterized by FT‐IR, XRD, SEM‐EDX, TEM, ICP‐OES and XPS techniques. 100 mg Fe3O4/SiO2−NH2/HB@Pd nanocomposite with Pd metal content of 6.00±0.14 catalyzed the hydrolysis of 10 mM AB at 25 °C with 100 % yield. The presented work includes the effect of catalyst amount and temperature on the rate of the hydrolysis reaction of AB. As a result of the kinetic studies, the activation energy (Ea) for the Fe3O4/SiO2−NH2/HB@Pd catalyzed AB hydrolysis reaction was calculated as 34±1 kJ.mol−1, and the TOF value was calculated as 133 mol H2.(mol Pd(0).h)−1. The designed heterogenous magnetic nanocomposite catalyst demonstrated significant catalytic activity for AB hydrolysis reaction at 25 °C.

Palladium Iodide‐Catalyzed Selective Carbonylative Double Cyclization of 4‐(2‐Aminophenyl)‐3‐yn‐1‐ols to Dihydrofuroquinolinone Derivatives

Comprehensive SummaryThe PdI2/KI‐catalyzed oxidative carbonylation of 4‐(2‐aminophenyl)‐3‐yn‐1‐ols, bearing two potential nucleophilic groups in suitable position selectively leads to dihydrofuroquinolinone derivatives in fair to high yields (60%—89%) and excellent turnover numbers (180—267 mol of product per mol of Pd) over 19 examples, through a mechanistic pathway involving initial O‐cyclization followed by N‐cyclocarbonylation. In such process, the selective catalytic construction of two rings and three new bonds is achieved in one synthetic step to afford high value added fused heterocyclic structures starting from readily available materials.

Novel Route to Cationic Palladium(II)-Cyclopentadienyl Complexes Containing Phosphine Ligands and Their Catalytic Activities.

The Pd(II) complexes [Pd(Cp)(L)n]m[BF4]m were synthesized via the reaction of cationic acetylacetonate complexes with cyclopentadiene in the presence of BF3∙OEt2 (n = 2, m = 1: L = PPh3 (1), P(p-Tol)3, tris(ortho-methoxyphenyl)phosphine (TOMPP), tri-2-furylphosphine, tri-2-thienylphosphine; n = 1, m = 1: L = dppf, dppp (2), dppb (3), 1,5-bis(diphenylphosphino)pentane; n = 1, m = 2 or 3: 1,6-bis(diphenylphosphino)hexane). Complexes 1-3 were characterized using X-ray diffractometry. The inspection of the crystal structures of the complexes enabled the recognition of (Cp-)⋯(Ph-group) and (Cp-)⋯(CH2-group) interactions, which are of C-H…π nature. The presence of these interactions was confirmed theoretically via DFT calculations using QTAIM analysis. The intermolecular interactions in the X-ray structures are non-covalent in origin with an estimated energy of 0.3-1.6 kcal/mol. The cationic palladium catalyst precursors with monophosphines were found to be active catalysts for the telomerization of 1,3-butadiene with methanol (TON up to 2.4∙104 mol 1,3-butadiene per mol Pd with chemoselectivity of 82%). Complex [Pd(Cp)(TOMPP)2]BF4 was found to be an efficient catalyst for the polymerization of phenylacetylene (PA) (catalyst activities up to 8.9 × 103 gPA·(molPd·h)-1 were observed).

Nearly monodisperse Cu|pd alloyed Nanocrystals: Ultrasound induced stepwise thermoreduction in organic Medium, and catalytic alcoholysis for hydrogen evolution

Active search for efficient and inexpensive catalyst is the basic premise and urgent requirement to promote the practicality of the new hydrogen storage material-ammonia borane. We herein propose an ultrasonic-induced stepwise thermoreduction protocol to fabricate serial bimetal Cu|Pd alloyed nanocrystals with various metal molar ratios, and scientifically evaluate respective catalytic activity for alcoholyzing ammonia borane. Comprehensive characterizations and analysis confirm that the as-fabricated Cu|Pd crystalline grains appear as nearly monodisperse microspheres with mean size of about 10 nm, taking on almost superlattice arrangement. The ultrasound and precursor molar ratio can affect grain size and dispersity to varying degrees. Regardless of the Pd/Cu molar ratio, alloy phase microstructure can be formed. The Pd-rich nanoagent Cu40Pd60 unfold the upmost catalytic ability for alcoholyzing ammonia borane, even exceeding Pd NCs, with the turnover frequency (TOF) value of 66.51 mol (H2)·min−1·(mol Pd)-1 and apparent activation energy of 30.35 kJ·mol−1. Moreover, the Cu40Pd60 nanocrystals possess the exceptional stability with only 10% loss of the original catalytic activity after 5 round cyclic utilization. The catalytic methanolysis at the given conditions is identified as first-order reaction. The current findings can enrich the family of the serial bimetal alloyed nanocatalyst, also offer an optional strategy for fabricating the poly-metal composite catalysts with high activity.

Direct Synthesis of Partially Chain-Straightened Propylene Oligomers and P-MA Co-Oligomers Using Axially Flexible Shielded Iminopyridyl Palladium Complexes.

In this study, a series of partially chain-straightened propylene oligomers and functional propylene−methyl acrylate (P-MA) co-oligomers were synthesized with 8-alkyl-iminopyridyl Pd(II) catalysts. The molecular weight and polar monomer incorporation ratio could be tuned by using Pd(II) catalysts with various 8-alkyl-naphthyl substituents (8-alkyl: H, Me, and n-Bu). In propylene oligomerization, all the 8-alkyl-iminopyridyl Pd(II) catalysts convert propylene to partially chain-straightened (119−136/1000 C) oligomers with low molecular weights (0.3−1.5 kg/mol). Among the catalysts, Pd1 with non-substituent (H) on the ligand showed the highest activity of 5.4 × 104 g/((mol of Pd) h), generating oligomers with the lowest molecular weight (Mn: 0.3 kg/mol). Moreover, polar-functionalized propylene-MA co-oligomers with very high incorporation ratios (22.8−36.5 mol %) could be obtained in the copolymerization using these 8-alkyl-iminopyridyl Pd(II) catalysts. Additionally, Pd1 exhibited the best performance in propylene-MA copolymerization as it displayed the highest MA incorporation ratio of up to 36.5 mol%. All the three catalysts are capable of generating partially chain-straightened P-MA co-oligomers and the activities decrease gradually while the molecular weight increases with the increasing steric hindrance of the alkyl substituent (H < Me < n-Bu). Compared to Pd4 with the rigid 8-aryl substituent, the flexible 8-alkyl-iminopyridyl Pd(II) catalysts (Pd1-3) not only showed much higher activities in the propylene oligomerization, but also yielded P-MA co-oligomers with significantly higher incorporation ratios in the propylene co-oligomerization.

Highly Efficient Hydrogen Production via the Hydrolysis of Ammonia Borane over Nanostructured Pd‐Cu Nanoparticles Supported on PDA‐coated Graphene

AbstractPalladium (Pd), copper (Cu) bimetallic alloy nanoparticles immobilized onto a PDA‐coated graphene support (Pd−Cu/PDA/RGO) hybrid was synthesized through co‐reduction of K2PdCl4 and Cu(NO3)2. The Pd to Cu ratio was rationally controlled to obtain the optimum Pd−Cu/PDA/RGO catalyst. The as‐prepared catalyst demonstrated good catalytic activity for hydrogen production by hydrolysis of ammonia borane, high turnover frequency (TOF) of 37.41 mol H2 per mol Pd−1 min−1 at 298 K and a low activation energy (Ea) of 47.97 kJ mol−1 were accomplished, these metrics were superior to that of Pd−Cu/RGO nanocatalysts. The comparative results indicate that the PDA‐coated graphene (PDA/RGO) support is pivotal for the catalytic activity of Pd−Cu/PDA/RGO for hydrolysis of ammonia borane. The PDA modified onto GO surface effectively disperse the alloy particles, therefore ensure more catalytic active sites responsible for ammonia borane hydrolysis. The tight anchoring of alloy nanoparticles also enabled excellent cyclic stability, 67.7 % of its initial catalytic activity could be maintained after ten cycles. The current work demonstrates the potential of Pd−Cu/PDA/RGO in active and durable ammonia borane hydrolysis for hydrogen production.

Norbornene and methyl methacrylate polymerizations catalyzed by palladium(II) complexes bearing aminomethylpyridine and aminomethylquinoline derivatives

A series of Pd(II) complexes, 1–4 bearing N,N-bidentate aminomethylpyridine and aminomethylquinoline derivatives were synthesized and characterized. Single crystal X-ray diffraction analysis demonstrated that tetra-coordinated Pd(II) complexes adopted distorted square planar geometries around the metal center. In the presence of modified methylaluminoxane (MMAO) as a co-catalyst, Pd(II) complexes 1–4 exhibited significant activities (up to 43.2×105 gPNB mol Pd−1 h−1) towards the addition polymerization of norbornene (NB) at 25 ℃. Insoluble poly(norbornene) (PNB) was obtained by all the tested catalytic systems, i.e., 1–4/MMAO. The catalytic capabilities of synthesized Pd(II) complexes were also tested towards methyl methacrylate (MMA) in the presence of modified methyl aluminoxane MMAO. Complex 3 with quinoline/piperidine functionalities showed the highest catalytic activity of 8.83×104 gPMMA mol Pd−1 h−1 at 60°C and resulted in high molecular weight PMMA (Mw = 2.16×106 g mol−1). All the complexes yielded syndiotactic poly(methyl methacrylate) (PMMA) (rr = 0.70). Notably, the steric bulk and electronic properties of the ligand framework affect their activities towards NB and MMA polymerizations, whereas, for PMMA, the stereoselectivities remained unaffected.

Competing commercial catalysts: Unprecedented catalyst activity and stability of Mizoroki-Heck reaction in a continuous packed bed reactor

• Supported Ionic Liquid Catalyst (SILCA) for the continuous Mizoroki-Heck reaction. • On-line UV–VIS spectrometry analysis for monitoring metal leaching. • Simple and long-performing processes for Mizoroki-Heck reaction in a continuous flow. Main obstacle for adopting continuous processes as a standard technology for Mizoroki-Heck reaction usually lies in its specific reaction mechanism. Here we present an important step forward answering the challenges unraveled through a comprehensive study that provides deeper understanding on the Mizoroki-Heck reaction, in particular the case when iodobenzene and butyl acrylate react in a continuous packed bed reactor in the presence of a Pd Supported Ionic Liquid Catalyst (SILCA). On-line UV–VIS spectrometry supported by ICP-OES, TEM and XPS measurements were carried out and the catalyst leaching was minimized. Finally, simple continuous flow process was proposed resulting in a high catalytic activity (up to 1470 mol ArI mol Pd −1 h −1 ) and reaching productivity in the range of 12,000 to 16,000 mol ArI mol Pd −1 thus competing with the performance of commercial catalysts.

Nitrogen-phosphorus co-functionalized reduced graphene oxide supported NiCoPd-CeOx nanoparticles as a highly efficient and stable catalyst for formic acid dehydrogenation

Formic acid (HCOOH, FA), a common liquid hydrogen storage material, has attracted tremendous research interest. However, the development of efficient, low-cost and high-stable heterogeneous catalyst for selective dehydrogenation of FA remains a major challenge. In this paper, a simple co-reduction method is proposed to synthesize nitrogen-phosphorus co-functionalized rGO (NPG) supported ultrafine NiCoPd-CeO x nanoparticles (NPs) with a mean size of 1.2 nm. Remarkably, the as-prepared Ni 0.2 Co 0.2 Pd 0.6 -CeO x /NPG shows outstanding catalytic activity for FA dehydrogenation, affording a high TOF value of 6506.8 mol H 2 mol Pd −1 h −1 at 303 K and a low activation energy of 17.7 kJ mol −1 , which is better than most of the reported heterogeneous catalysts, and can be ascribed to the combined effect of well-dispersed ultrafine NiCoPd-CeO x NPs, modified Pd electronic structure, and abundant active sites. The reaction mechanism of dehydrogenation of FA is also discussed. Furthermore, the optimized Ni 0.2 Co 0.2 Pd 0.6 -CeO x /NPG shows excellent stability over 10 th run with 100% conversion and 100% H 2 selectivity, which may provide more possibilities for practical application of FA system on fuel cells. • N–P co-functionalized rGO supported ultrafine NiCoPd-CeO x NPs are successfully synthesized via a simple co-reduction method. • NPG has a positive effect on improving the distribution and controlling particle size. • The Ni 0.2 Co 0.2 Pd 0.6 -CeO x /NPG exhibits high activity towards FA dehydrogenation, giving a TOF of 6506.8 h −1 at 303 K. • The Ni 0.2 Co 0.2 Pd 0.6 -CeO x /NPG shows excellent stability and activity even after 10 th run.

Palladium nanoparticles supported on multı-walled carbon nanotube (MWCNT) for the catalytic hexavalent chromium reduction

Chromium (VI) is widely accepted as an acute toxic contaminant in living ecosystems, while the trivalent Chromium form (III) is thought to be an important element for living beings. This study showed that zero palladium (Pd0) metal nanoparticles supported onto a multi-walled carbon nanotube (MWCNT) catalyst (Pd@MWCNT) effectively catalyzed the reduction reaction of Chromium (VI) to Chromium (III) using HCOOH (formic acid) as a reducing agent. The catalyst (Pd@MWCNT) was prepared reproducibly in the aqueous mixture at room conditions through the impregnation-reduction technique and identified using some analytical characterization techniques (HRTEM, DR/UV–vis, TEM-EDX, TEM, XPS, ICP-OES, and P-XRD). The results of the characterization studies show that the palladium(0) nanoparticles (demean = 2.20 ± 0.25 nm) are very well dispersed onto the MWCNT support material surface. The stability and activity of catalytic performance of Pd(0) metal nanoparticles were investigated in the reactions of Chromium (VI) to Chromium (III) in HCOOH solution. The results show that the Pd@MWCNT catalyst exhibited excellent activity (TOF = 281 mol Cr2O72−/mol Pd min), even after 5 times of reuse (<86%) in the reduction reaction of Chromium (VI) to Chromium (III) at 298K. In addition, this study includes very rich kinetic data depending on [Pd@MWCNT], [HCOOH], [HCOONa], [Cr2O72−] concentrations and temperature parameters to determine the nature of the reduction rate and activation parameters of Cr(VI) catalyzed by Pd@MWCNT nanocatalyst in the formic acid medium as a reducing agent.

Homo‐ and Copolymerization of Norbornene with Allyl Palladium and Nickel Complexes Bearing Imidazo[1,5‐a]pyridine Sulfonate Ligands

AbstractA series of allyl palladium and nickel complexes based on imidazo[1,5‐a]pyridine sulfonate ligands were synthesized. All these complexes were fully characterized by 1H and 13C NMR, elemental analysis, and high‐resolution mass spectrometry (HRMS). By treatment with Me2AlCl, palladium complexes showed high activities (up to 4.5×107 g of PNB (mol of Pd)−1 h−1) in norbornene polymerization, and the steric hindrance of the catalysts had little effect on the catalytic activities. They could also catalyze the copolymerization of norbornene with butyl vinyl ether (BVE) and ester monomers, but could not catalyze the copolymerization of norbornene with allyl butyl ether (ABE). In addition, the catalytic activities of nickel complexes for norbornene polymerization were similar to that of palladium complexes upon activation with MAO. They could catalyze copolymerization of norbornene with BVE and ABE, but not with ester monomers. In nickel system, the lower steric hindrance of the substituent led to higher activity.

Structurally Disordered Pd−P Nanoparticles as Effective Catalysts for the Production of Hydrogen Peroxide by the Anthraquinone Method

AbstractThe properties of the catalyst based on structurally disordered Pd−P nanoparticles supported on a carbon support (Pd−P/C) in the preparation of hydrogen peroxide by the anthraquinone method have been studied. It is shown that a high yield of H2O2 is observed upon sequential hydrogenation of 2000 mol of eAQ (mol Pd)−1. The H2O2 yield reaches 96 %–97 %. Pd−P nanoparticles are more active in the hydrogenation of 2‐ethyl‐9,10‐anthraquinone than Pd6P crystalline phosphide. In terms of H2O2 yield, Pd−P/C catalysts are superior to known catalysts: Pd/C, Pd/Al2O3. Based on the data of X‐ray powder diffraction, X‐ray photoelectron spectroscopy, Inductively Coupled Plasma and thermogravimetry, the main reasons for the deactivation of Pd−P/C catalysts have been established. Crystallization of the structurally disordered Pd−P nanoparticles, poisoning by eAQ conversion products and leaching of the active component are considered to be possible reasons of the Pd−P/C catalyst deactivation.

Monometallic and heterobimetallic ruthenium (II) and palladium (II) complexes based on a pyridine‐hydrazone ligand as bifunctional catalysts for ROMP of norbornene and ethylene polymerization

AbstractThe monometallic complex [Pd(L)(PPh3)] (mono‐Pd) was synthesized using a potentially tridentate hydrazone (H2L) and used as precursor to prepare a heterobimetallic ruthenium (II)‐palladium (II) complex [Cl2(p‐cymene)Ru(μ‐L)Pd (PPh3)] (Ru‐Pd). Mono‐Pd and Ru‐Pd were characterized by fourier transform infrared spectroscopy (FTIR), ultraviolet‐visible spectroscopy (UV–Vis), 1H, 13C{1H} and 31P{1H} nuclear magnetic ressonance(NMR) spectroscopy, elemental analysis, cyclic voltammetry, matrix‐assisted laser desorption/ionization ‐ time of flight (MALDI‐TOF) mass spectrometry, and computational methods. The mono‐Pd was additionally studied by single‐crystal X‐ray diffraction. The complex [RuCl2(p‐cymene)(Isoniazid)] (mono‐Ru) was also obtained following literature methods aiming a comparison in the catalytic activity. The ring opening metathesis polymerization (ROMP) of norbornene (NBE) using mono‐Ru or Ru‐Pd as precatalysts in the presence of ethyl diazoacetate (EDA) was evaluated as a function of time (10–60 min) using [NBE]/[EDA]/[Ru] = 5000/28/1 at 50°C. The time increases produced good yields of polyNBE, reaching 38% and 46% for mono‐Ru and Ru‐Pd, respectively. The polyNBE produced was measured by size‐exclusion chromatography (SEC) and reached an order of magnitude of 105 g·mol−1 of Mn, with Ð values ranging from 2.51 to 1.86 for mono‐Ru and from 3.50 to 1.66 for Ru‐Pd. The catalytic activity of mono‐Pd and Ru‐Pd on ethylene polymerization was assessed with a range of [Al]/[Pd] molar ratio between 350 and 1750, 30–70°C temperature, 2 to 4 h reaction time, and total reaction volume of 25 and 50 ml. Mono‐Pd achieved an activity of 22.80 kg PE (mol Pd)−1 h−1 at 60°C after 4 h using [Al]/[Pd] = 1050, 7 μmol of catalyst in 25 ml of toluene, and 116 psi ethylene. For Ru‐Pd, an activity of 20.35 kg PE (mol Pd)−1 h−1 at 60°C after 4 h was obtained using [Al]/[Pd] = 1750, 7 μmol of catalyst in 25 ml of toluene, and 116 psi ethylene. Overall, Ru‐Pd showed to be active in both ROMP and ethylene polymerization reactions, being categorized as a bifunctional catalyst.

Nanometals Templated by Tobacco Mosaic Virus Coat Protein with Enhanced Catalytic Activity

Bio-nano hybrid materials feature eco-friendly synthesis, various self-assembly patterns and numerous possibilities of surface functionalization. Owing to these unique advantages, biological scaffolds have been be regarded as green alternatives to fabricate metallic nanomaterials for catalytic applications. In this study, a bulky tobacco mosaic virus coat protein (TMVCP) has been employed as a versatile template to synthesize nanometals (Pd, Pt and Au) in alkaline buffer at room temperature. Protein-functionalized nanoparticles (NPs) with ca. 3 nm in diameter were obtained with uniform size distributions. These materials are green catalytic systems with exceptional performance for small organic molecule transformations in water. Remarkably, while Au NPs showed rapid kinetics in 4-nitrophenol reduction (rate constant with Au NPs: 0.01862 s-1), Pd NPs exhibited superior catalytic activity towards hydrogenation of allyl alcohol (Turnover frequency of Pd NPs: 6382 ± 200 mol product (mol Pd * h)-1) and a set of derivatives. The enhanced catalytic performance is strongly related to the protein ligand. To ascertain the protein structure-function effect on the catalytic performance, an in-depth analysis was performed for the TMVCP-Pd NP system via molecular dynamic (MD) simulations. Our results suggest that due to the moderate interaction between Pd and protein and the steric hindrance of the bulky protein, a large portion of the Pd NP surface remains approachable for the reactant molecules, thus resulting in enhanced reaction rate.

Synthesis of mononuclear and dinuclear palladium (II) complexes containing oxadithioether ligands and their catalytic activities in norbornene polymerization

AbstractThe Pd (II) complexes trans‐[PdCl2(μ‐L)]2 and [Pd(acac)(L)][BF4] (L = RS(CH2)2O(CH2)2SR, R = Me, Et, nPr, iPr, nBu, iBu, n‐hexyl, benzyl) were obtained through the reaction of Pd(cod)Cl2 or [Pd(acac)(MeCN)2][BF4] with one equivalent of oxadithioether (L). The structural features of these complexes were analyzed by nuclear magnetic resonance (NMR) and Fourier‐transform infrared spectroscopy (FTIR), as well as electrospray ionisation mass spectrometry and density functional theory calculations. The complexes di‐μ‐(2,10‐dimethyl‐6‐oxa‐3,9‐dithiaundecane‐κ2S,S′)‐bis[trans‐dichloropalladium (II)] and (acetylacetonate‐κ2O,O′)(2,10‐dimethyl‐6‐oxa‐3,9‐dithiaundecane‐κ2S,S′)palladium (II) tetrafluoroborate were characterized by X‐ray diffractometry. The X‐ray structures of each complex indicate an axial M–O interaction formed by the endodentate conformation of the oxadithioether ligand. Palladium (II) dichloride complexes with oxadithioethers were demonstrated to have a 16‐membered dinuclear structure with a trans‐configured S2PdCl2 fragment. In the case of cationic palladium acetylacetonate complexes, only mononuclear complexes with a cis configuration of the oxadithioether fragment were observed. Variable temperature 1H and 13C NMR studies of the complexes demonstrate dynamic bonding of the oxadithioether ligands consistent with the presence of diastereoisomers that differ in the orientation of the S‐R groups along with both endodentate and exodentate bonding modes in solution. FTIR studies of the complexes indicate the presence of isomers in the solid state. The palladium catalyst precursors trans‐[PdCl2(μ‐L)]2 and [Pd (acac)(L)][BF4] were found to be active in the addition polymerization of norbornene. In the presence of cocatalysts, such as diisobutylaluminum chloride and boron trifluoride etherate, Pd (II) complexes exhibited activities in the range of 105 to 107 g of polymer (mol of Pd)−1 h−1. The catalyst systems showed good thermostability with a high activity of 1.43 × 107 g of polymer (mol of Pd)−1 h−1 at 75°C. These complexes are examples of Pd (II) complexes bearing thioether ligands, which are rarely observed in the field of olefin polymerization.

Synthesis of palladium complexes with quinolino-based tridentate ligands and their applications for norbornene polymerization

Palladium complexes bearing new tridentate quinolino-based [N−NNox] ligands were synthesized and tested for the polymerization of norbornene. Upon activation of MAO, all the palladium complexes showed high catalytic activities for the vinyl-addition polymerization of norbornene up to 11.5 × 106 g of PNB (mol of Pd)−1h−1. The structure–activity relationships in the polymerization of norbornene, namely steric and electric effects of the ligands, were carefully investigated.

Cationic palladium(II)–acetylacetonate complexes containing phosphine and aminophosphine ligands and their catalytic activities in telomerization of 1,3-butadiene with methanol

The Pd(II) complexes [Pd(acac)(L)n]BF4 were synthesized by the reaction of [Pd(acac)(MeCN)2]BF4 with L (n = 2: L = PCyPh2, PCy2Ph, P(NMe2)3, P(NEt2)3, tri-2-furylphosphine, tri-2-thienylphosphine; n = 1: L = 2 dicyclohexylphosphino-2′,6′-dimethoxybiphenyl, 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl). The structural features of the complexes were analyzed by NMR and FTIR spectroscopies. Complexes [Pd(acac)(PCyPh2)2]BF4 and [Pd(acac)(PCy2Ph)2]BF4 were characterized by X-ray diffractometry. The cationic palladium catalyst precursors were found to be active catalysts for telomerization of 1,3- butadiene with methanol under base-free conditions. Complexes [(acac)Pd(PCy2Ph)2]BF4 and [(acac)Pd(TOMPP)2]BF4 in terms of yield, selectivity, and stability are effective for the catalytic telomerization (TOMPP = tris(2-methoxyphenyl)phosphine). Using 0.001–0.0025 mol% palladium loading methoxy-2,7-octadienes were obtained with chemoselectivities of 76–94% and TON up to 60000 mol 1,3-butadiene per mol Pd.

Synthesis and Catalytic Properties of Cyclopalladated Complexes Bearing a Phosphane‐Sulfonate Ligand

Reactions of the phosphane‐sulfonate ligand with [Pd(OAc)(8‐Me‐quin‐H)]2 or [Pd(dmba)(µ‐Cl)]2 (dmba = Me2NCH2C6H5) in acetonitrile afforded the corresponding C(sp3),N‐chelated palladacycle Pd1 and C(sp2),N‐chelated palladacycle Pd2 in high yields. Both complexes have been fully characterized by 1H and 13C NMR, high‐resolution mass spectrometry (HRMS), and elemental analysis. The molecular structure of Pd1 was further confirmed by single‐crystal X‐ray diffraction analysis. With Et2AlCl as cocatalyst, these complexes showed moderate catalytic activities for the addition polymerization of norbornene. While with methylaluminoxane (MAO) as cocatalyst, they showed high catalytic activities (up to 5.80 × 107 g of PNB (mol of Pd)–1 h–1) at higher temperatures (above 100 °C). The C(sp3),N‐chelated palladacycle Pd1 exhibited marked higher activities than the C(sp2),N‐chelated palladacycle Pd2, whether Et2AlCl or MAO was used as cocatalyst.