Palladium Complexes 3a Research Articles

An efficient palladium catalyzed mizoroki-heck cross-coupling in water: synthesis, characterization and catalytic activities

A series of new palladium complexes known as PEPPSI-type complexes 3 were successfully synthesized by reacting benzimidazolium salts 2a-e, potassium carbonate (K2CO3), and palladium chloride (PdCl2) in pyridine for 16 h at 80 °C. Both the benzimidazolium salts 2a-e and the resulting complexes 3 were characterized through spectroscopic data and elemental analysis. The Mizoroki-Heck coupling reaction, catalyzed by the homogeneous Pd, was effectively carried out in water without the need for any additional substances under aerobic conditions. The optimization of various key reaction parameters was performed to enhance the yield of the desired cross coupling product. The catalytic performance of these complexes in a catalytic system containing palladium complexes 3a, Et3N, and H2O was evaluated in the Mizoroki-Heck coupling reaction. The PEPPSI-type palladium complex 3a /Et3N/H2O/98 °C catalyst system exhibited high activity, with a turnover frequency (TOF) ranging from 12 to 14 /hour towards achieving the excellent yield of the Mizoroki-Heck coupling products for a wide range of electron withdrawing as well as electron donating aryl bromide and chlorides in shortest reaction time.

From synthesis to biological impact of palladium bis(benzimidazol-2-ylidene) complexes: Preparation, characterization, and antimicrobial and scavenging activity

Abstract Palladium-based complexes with the ligand N-heterocyclic carbene have long received attention as active catalysts for many catalytic reactions. Recently, the biological activities of these air- and moisture-stable complexes have also been investigated. In our work, bis(benzimidazol-2-ylidene)palladium complexes 3a–d were synthesized by reacting benzimidazolium salts 2a–d with PdCl2 under reflux in tetrahydrofuran for 24 h and analyzed by spectroscopy (FT-IR [Fourier transform infrared], 1H NMR [proton nuclear magnetic resonance]) characterization, 13C NMR [carbon-13 (C13) nuclear magnetic resonance]), and elemental analysis. The in vitro antibacterial and antifungal activities of these complexes were studied against Gram-positive and Gram-negative microorganisms, and two different fungi showed their remarkable biological potential. In addition, the analysis of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals using spectrophotometry showed that they are an antioxidant. The potent antibacterial and antioxidant activities of the synthetic complexes suggest that they are more effective antibacterial agents. Our study extends the biological relevance of palladium bis(benzimidazol-2-ylidene) complexes with antibacterial and antioxidant activities. Furthermore, the main goal of the docking simulation is to provide a detailed analysis of the interaction between the complex and the protein of interest.

Preparation and characterization of PEPPSI-palladium N-heterocyclic carbene complexes using benzimidazolium salts catalyzed Suzuki–Miyaura cross coupling reaction and their antitumor and antimicrobial activities

New palladium complexes were efficiently synthesized from the reaction of benzimidazolium salts 2a–e, potassium carbonate (K2CO3) and palladium chloride (PdCl2) in pyridine (for 3a–e). The catalytic activity of these complexes in a catalytic system including palladium complexes and K2CO3 in DMF-H2O was evaluated in Suzuki–Miyaura cross-coupling reactions of aryl bromides and chlorides with phenylboronic acid. Our novel complexes show excellent catalytic activities with high turnover numbers (TON) and high turnover frequencies (TOF) (e.g. for the Suzuki–Miyaura reaction: TON up to 370 and TOF up to 123.3 h−1). Both benzimidazolium salts 2a–e and complexes 3 have been characterized using spectroscopic data and elemental analysis. The antimicrobial activity of the N-heterocyclic carbene palladium complexes 3a–e varies with the nature of the ligands. Also, the IC50 values of both, complexes (3a–e) and benzimidazoles 2a–e, have been determined. In addition, the new palladium complexes were screened for their antitumor activity. Complexes 3e and 3d exhibited the highest antitumor effect with IC50 values 6.85 μg/mL against MCF-7 and 10.75 μg/mL against T47D, respectively.

ChemInform Abstract: Acyclic Aminocarbene‐Like Palladium Complex‐Catalyzed Suzuki—Miyaura Reaction at Low Catalyst Loadings.

Abstract A series of air-stable aminocarbene-like palladium(II) complexes were easily prepared by the reaction of bis-aromaticisocyanide-dichloropalladium(II) with N-arylbenzamidines. 0.1 mol % of the optimal palladium complex 3a showed excellent catalytic activity for Suzuki–Miyaura cross-coupling reaction at room temperature and the desired products were isolated in up to 98% yields. Moreover, a large-scale reaction showed that 0.01 mol % 3a was enough to catalyze the coupling reaction efficiently at room temperature to give the desired product in 93% yield.

Synthesis, Structures, and Norbornene Polymerization Behavior of Palladium Complexes Bearing Tridentate o-Aryloxide-N-heterocyclic Carbene Ligands

A series of new pincer-type tridentate o-aryloxide-N-heterocyclic carbene ligands 2a–d were synthesized. Treatment of the proligands with Ag2O and (COD)PdCl2 afforded the desired o-aryloxide-NHC tridentate palladium complexes 3a–d in high yields (NHC = N-heterocyclic carbene). In comparison with the above tridentate complexes, bidentate bis(aryloxide-NHC) palladium complex 3e was also synthesized. All of these complexes were fully characterized by 1H and 13C NMR spectroscopy, high-resolution mass spectrometry, and elemental analysis. The molecular structures of 3a,b,d,e were determined by single-crystal X-ray diffraction analysis. On activation with either methylaluminoxane (MAO) or diethylaluminum chloride (Et2AlCl), all palladium complexes exhibited excellent activities of up to 5.99 × 107 g of PNB (mol of Pd)−1 h–1 toward norbornene addition polymerization, and the monomer conversion is up to 99.9%. Notably, the tridentate palladium complexes show better activities than the corresponding bidentate bis(...

Acyclic aminocarbene-like palladium complex-catalyzed Suzuki–Miyaura reaction at low catalyst loadings

A series of air-stable aminocarbene-like palladium(II) complexes were easily prepared by the reaction of bis-aromaticisocyanide-dichloropalladium(II) with N-arylbenzamidines. 0.1 mol% of the optimal palladium complex 3a showed excellent catalytic activity for Suzuki–Miyaura cross-coupling reaction at room temperature and the desired products were isolated in up to 98% yields. Moreover, a large-scale reaction showed that 0.01 mol% 3a was enough to catalyze the coupling reaction efficiently at room temperature to give the desired product in 93% yield.

Synthesis of [N,P] ligands based on pyrrole. Application to the total synthesis of arnottin I

This paper describes the synthesis of a new class of [N,P] ligands based on pyrrole with a dimethylamino group as hard donor and a phosphine moiety as soft base. We have also modified the phosphine fragment to change the electronic and steric properties of these ligands. Palladium complex 3a proved to be very efficient in Heck cross-coupling reactions and in intramolecular aryl–aryl couplings of esters and amides. We have demonstrated the applicability and efficiency of this novel catalyst in the total synthesis of the natural product arnottin I.

Synthesis and Characterization of Nickel(II) and Palladium(II) Complexes based on Tridentate [N–NP] and [N–NS] Ligands and Their Applications in Norbornene Polymerization

The series of anilido-imine N–NP and N–NS tridentate nickel and palladium complexes [(ArNHC6H4CH═NPh-2-XPh)MCl] (X = PPh, Ar = 2,6-Me2C6H3, M = Ni (2a), X = PPh, Ar = 2,6-Et2C6H3, M = Ni (2b); X = PPh, Ar = 2,6-i-Pr2C6H3, M = Ni (2c); X = S, Ar = Ph, M = Ni (2d); X = S, Ar = 2,6-Me2C6H3, M = Ni (2e); X = S, Ar = 2,6-i-Pr2C6H3, M = Ni (2f); X = PPh, Ar = 2,6-Me2C6H3, M = Pd (3a); X = PPh, Ar = 2,6-Et2C6H3, M = Pd (3b); X = PPh, Ar = 2,6-i-Pr2C6H3, M = Pd (3c)) were synthesized. All the complexes were fully characterized by IR, NMR and elemental analyses. X-ray diffraction analyses on complexes 2a,c and 3a revealed an almost square-planar coordination of the central metal. After activation with methylaluminoxane (MAO), the nickel(II) complexes 2a–f can be used as catalysts for norbornene polymerization to produce vinyl addition type polynorbornene (PNB) with high catalytic activities, up to 5.82 × 107 g of PNB (mol of Ni)−1 h–1, while poor catalytic activities are found for the palladium complexes 3a–c.

Synthesis and characterization of novel chiral NHC–palladium complexes and their application in copper-free Sonogashira reactions

A new series of chiral N-heterocyclic carbene (NHC) palladium complexes were synthesized from a relatively inexpensive amino acid, l-phenylalanine. All these compounds were fully characterized by (1)H-NMR, (13)C-NMR and elemental analysis. The X-ray molecular structures of two of the complexes were reported. The catalytic activity of the four palladium complexes was successfully tested in the Sonogashira reaction under copper free conditions in air. The palladium complex 3a provided good activity in the Sonogashira coupling reaction.

Palladium Alkynyl and Allenylidene Complexes: Very Efficient Precatalysts for C–C Coupling Reactions

Oxidative addition of BrC CC(=O)O-menthyl (1a) to [Pd(PPh3)(4)] affords the alkynyl complex trans-[Br(PPh3)(2)Pd-C CC(=O)O-menthyl] (2a). Subsequent reaction of 2a with trifluoroacetate gives trans-[(F3CCOO)(PPh3)(2)Pd-C CC(=O)O-menthyl] (3a). Reaction of trans-[Br(PPh3)(2)Pd-C CC(=O)NC4H8] (2b) with 10 equiv of NaI gives trans-[I(PPh3)(2)Pd-C CC(=O)NC4H8] (4b). The efficiency of the new palladium complexes 3a and 4b as precatalysts is compared with that of recently published cationic palladium allenylidene complexes in C-C coupling reactions. Further trans-bis(alkynyl)palladium complexes, trans-[(PEt3)(2)Pd(-C CC{=O}NR2)(2)] (NR2 = N(CH2)(4) (9b), NMe2 (9c), N(CH2)(4)O (9d), N(CH2)(5) (9e)), trans-[((PPr3)-Pr-i)(2)Pd(-C CC{=O}NMe2)(2)] (11c), and trans-[(PPh3)(2)Pd(-C CC{=O}NR2)(2)] (NR2 = N(CH2)(4) (13b), NMe2 (13c), N(CH2)(4)O (13d)), were synthesized by treating HC CC(=O)NR2 with AgNO3 followed by transmetalation of the alkynyl ligand from silver to [PdCl2(PEt3)(2)], [PdCl2((PPr3)-Pr-i)(2)], or [PdCl2(PPh3)(2)], respectively. Methylation of complexes 9b-e with MeOTf yields dicationic bis(allenylidene) complexes of palladium, trans-{(PEt3)(2)Pd{=C=C=C(OMe)NR2}(2)](2+)(OTf)(2)(-) (NR2 = N(CH2)(4) (10b-OTf), NMe2 (10c-OTf), N(CH2)(4)O (10d-OTf), N(CH2)(5) (10e-OTf). Allcylation of complex 9e with [Me3O]BF4 or [Et3O)BF4 gave trans-[(PEt3)(2)Pd{=C=C=C(OR)N(CH2)(5)}(2)](2+)(BF4)(2)(-) (R = Me (10e-BF4), Et (10e'-BF4)). Complexes 11c and 13b-d were methylated accordingly to obtain the corresponding bis(allenylidene) complexes 12c-OTf, 12c-BF4, 14b-OTf, 14c-OTf, and 14d-OTf The catalytic activities of the new bis(alkynyl) and bis(allenylidene) complexes were investigated and compared with those of the mono(alkynyl) and mono(allenylidene) complexes. The palladium alkynyl and allenylidene complexes are both found to be very efficient precatalysts for Heck, Suzuki, and Sonogashira reactions. Even aryl chlorides were efficiently coupled in Heck and Suzuki reactions when complex 9e was used as precatalyst. Powder diffraction, TEM, and DLS measurements indicate that palladium nanoparticles are not formed during catalysis in the Heck reaction.

(Phenylalkyl)palladium Complexes Containing β-Hydrogen Atoms: Synthesis and Characterization of [PdR2(dppe)], [PdR(SPh)(dppe)] (R = CH2CH2Ph, CH2CH2CH2Ph, CH2CHMePh), and [Pd(CH2CH2CH2Ph)X(dppe)] (X = I, Br, Cl)

Reactions of HgR2 (R = CH2CH2Ph, 1a; CH2CH2CH2Ph, 1b; CH2CHMePh, 1c) (prepared from HgCl2 and the requisite Grignard compounds) with lithium in toluene afforded (phenylalkyl)lithium compounds LiR (2a−c) in yields of between 64 and 81%. At −30 °C, they react with [PdCl2(dppe)] [dppe = 1,2-bis(diphenylphosphanyl)ethane] yielding bis(phenylalkyl)palladium(II) complexes [PdR2(dppe)] (3a−c) which were isolated (Tdec = 159 °C, 3a; 80 °C, 3b; 145 °C, 3c) and fully characterized by 1H, 13C, and 31P NMR spectroscopy. Single-crystal X-ray diffraction of [Pd(CH2CH2Ph)2(dppe)] (3a) showed that the palladium atom is square-planar coordinated by two 2-phenylethyl ligands and the dppe ligand. The two CH2CH2Ph ligands exhibite nearly a fully staggered conformation. Overall, a good approximation for the complex is that it has C2 symmetry with the C2 axis defined by the Pd atom and the midpoint of the central C−C bond of the dppe ligand. Bis(phenylalkyl)palladium complexes 3a and 3b reacted with PhSH in a 1:1 ratio yielding [PdR(SPh)(dppe)] (R = CH2CH2Ph, 5a; CH2CH2CH2Ph, 5b), whereas in the case of complex 3c, besides [Pd(CH2CHMePh)(SPh)(dppe)] (5c), a considerable amount of [Pd(SPh)2(dppe)] (6a) was formed. Reactions of 3b with the less acidic alkanethiols iPrSH and tBuSH resulted in the formation of [Pd(CH2CH2CH2Ph)(SR′)(dppe)] (R′ = iPr, 5d; tBu, 5e) along with smaller amounts of [Pd(SR′)2(dppe)] (6) and [Pd(dppe)2] (7). Furthermore, complex 3b was found to react in THF with disulfides R′SSR′ (R′ = Ph, Bz, Me), yielding [Pd(CH2CH2CH2Ph)(SR′)(dppe)] (R′ = Ph, 5b; Bz, 5f, Me, 5g) with small amounts (3−13%) of [Pd(SR′)2(dppe)] (6) as side products. The corresponding reaction with MeSeSeMe afforded [Pd(CH2CH2CH2Ph)(SeMe)(dppe)] (8a) and 3% of [Pd(SeMe)2(dppe)] (9a) and [Pd(dppe)2] (7). Reactions of complex 5b with MeI and H2C=CHCH2Br in tetrahydrofuran and with neat H2C=CHCH2Cl readily proceeded at −30 °C to give halo(3-phenylpropyl)palladium complexes [Pd(CH2CH2CH2Ph)X(dppe)] (X = I, 10a; Br, 10b; Cl, 10c). They were isolated as pale yellow powdery/microcrystalline substances and fully characterized by 13C and 31P NMR spectroscopy. Solutions of complexes 10 in THF decompose rapidly above −30 °C. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Oxidative Addition of Aryl and Benzyl Trifluoroacetates to Zerovalent Palladium Complexes with Two Modes of C–O Bond Cleavage Processes

Abstract The aryl trifluoroacetates oxidatively added to a zerovalent palladium complex 2a with acyl-O bond cleavage under mild conditions to give the corresponding trans-(aryloxo)(trifluoroacetyl)palladium complexes 3a—3c. But 4-nitrophenyl trifluoroacetate reacted with 2a to yield cis-[Pd(OC6H4-4-NO2)2(PMe3)2] 3d, which was produced with C–O bond activation followed by disproportionation reaction. In contrast, benzyl trifluoroacetates reacted with the Pd(0) complex with benzyl–O bond fission to form benzyl(trifluoroacetato)palladium complexes 4a—4d. Complexes 4a—4d are in equilibrium in solutions between trans and cis isomers, with the proportion of the cis isomer increasing in polar solvents. Palladium-catalyzed carbonylation of benzyl trifluoroacetate has been achieved in the presence of benzyl alcohol and triethylamine to yield benzyl phenylacetate.

Preparation of Acyl(carboxylato)bis(tertiary phosphine)palladium(II) Complexes by C–O Bond Cleavage of Carboxylic Anhydrides on Interaction with Palladium(0) Complexes. Catalytic Hydrogenation of Carboxylic Anhydrides to Aldehydes by Palladium Complexes

Abstract Acyclic anhydrides oxidatively added to [Pd(styrene)(PMeR2)2] (R = Me, 2a; Ph, 2b) under mild conditions with C–O bond cleavage to give the corresponding trans-acyl(carboxylato)palladium complexes 3a—3h. Cyclic acid anhydrides also added to 2a to yield trans-acyl(carboxylato)palladium complexes 4a—4c, while reaction of 2a with phthalic anhydride afforded the palladalactone 4d generated via oxidative addition followed by decarbonylation. The acetyl(acetato)palladium complex 3a reacted with dihydrogen or formic acid to give acetaldehyde and acetic acid. Catalytic hydrogenation of acyclic anhydrides by a palladium complex was achieved to form the corresponding aldehydes and carboxylic acids.