Diimine Palladium Research Articles

Palladium(II) based imines; synthesis, characterization, X-Ray structural analysis; DFT and catalytic hydrogenation study

Based on the bridge alkyl chain length between the two azomethine linkages of the bis ortho naphtholimine ligands, two synthetic techniques were used to prepare a novel series of palladium(II) complexes. The molecular formulae of the isolated metal chelates were assigned based on thermal analysis (TGA and DTA) and analytical data. In addition comprehensive spectroscopic studies such as UV-Vis, IR, PXRD and X-ray single crystal have completed the structural formulations of the newly synthesized palladium(II) complexes in question. The best description of the overall molecular geometry of the palladium(II) center is the square planar as expected for the d8 center of palladium(II). DFT calculations were performed to correlate the structural properties of the present palladium(II) complexes with their catalytic activity towards the hydrogenation of cyclohexene. In addition, the optimized geometrical parameters deduced from the X-ray measurements for structural analysis are compared with the corresponding ones obtained by DFT calculations. Regarding complex 3, DFT calculations were carried out to decide the most appropriate molecular structure. The current square planar diimine palladium(II) complexes have been evaluated for the catalytic hydrogenation of mono olefin cyclohexene. The catalytic activity was studied in relation to the effect of catalyst structure, catalysis type, nature and amount of the solvents and co-solvents. The results obtained indicated that these complexes are pre-catalysts that efficiently catalyze hydrogenation of cyclohexene by H2 at mild conditions.

Copolymerization of 1-Decene with Alkyl and Alkenyl Methacrylates Catalyzed by Palladium–diimine Complexes

Copolymerization of 1-Decene with Alkyl and Alkenyl Methacrylates Catalyzed by Palladium–diimine Complexes

Benchmark study of density functionals for the insertions of olefin and polar monomers catalyzed by α–diimine palladium complexes

The performance of density functionals has been tested for the insertions of ethylene, methyl acrylate (MA), and vinyl bromide (VB) catalyzed by α-diimine palladium complexes. By screening 67 density functionals and comparing with experimental data, 7 hybrid GGA and 4 hybrid meta-GGA functionals showed better performance in the insertions of both ethylene and MA, and could be therefore suitable for ethylene-MA copolymerization. Meanwhile, three GGA (PW91PW91, HCTH, HCTH407), two meta-GGA (TPSSTPSS, tHCTH), 4 hybrid GGA and 6 hybrid meta-GGA functionals perform well in ethylene-VB copolymerization. Besides, nine D3 or D3BJ augmented functionals are found to be suitable for both copolymerization systems. The D2 dispersion correction overestimated insertion energy barriers of these monomers and is unsuitable for such copolymerization. In addition, the double-zeta basis set is found to be sufficient for solvation single-point calculation of these systems.

Catalytic Chain Transfer Polymerization to Functional Reactive End Groups for Controlled Free Radical Growth

Alkoxyamine-functionalized silane functions as a chain transfer reagent in ethylene polymerization catalyzed by cationic palladium diimine complexes, without significant adverse effects in producti...

Fabrication and Application of Graphene Supported Diimine‐Palladium Complex Catalyst for Organic Synthesis

AbstractIn this paper, a diimine palladium complex with suitable steric hindrance of isopropyl groups and electron supply provides excellent protection for palladium active centers was synthesized and anchored on graphene oxide (GO) to obtain a reusable heterogeneous catalyst (Pd‐DI@GO). The XPS results confirmed the effective loading of palladium and the interaction between palladium and ligand. The ICP‐AES data verified the Pd content of catalyst was 5.04 wt% and confirmed extremely small amount Pd leaching in Suzuki reaction (<1 ppm). The Pd‐DI@GO can catalyze Suzuki reaction under milder conditions and afford 39 reactants with high yields (79%∼99%). It can achieve a yield as high as 99% with heterocyclic compound reactants which can poison the catalyst. The yields of double and triple substitutions are also impressive (70∼92%). The Pd‐DI@GO can catalyze the C−H direct arylation reaction efficiently, affording 22 reactants with superior yields (>85%). Notably, the Pd‐DI@GO can be recycled after Suzuki reaction via filtration or centrifugation easily, presenting a yield above 90% for the 4th run.

Metal–organic insertion light initiated radical (MILRad) polymerization: photo-initiated radical polymerization of vinyl polar monomers with various palladium diimine catalysts

The photoinitiated radical polymerization pathway of MILRad polymerization towards its ability to polymerize a variety of vinyl polar functional monomers is investigated.

Nickel and palladium complexes with fluorinated alkyl substituted α-diimine ligands for living/controlled olefin polymerization

Living/controlled olefin polymerization is displayed by novel nickel and palladium diimine catalysts with fluorinated tails.

Ligand-Promoted Direct C–H Arylation of Simple Arenes: Evidence for a Cooperative Bimetallic Mechanism

A highly efficient catalyst for the direct C–H arylation of simple arenes was developed on the basis of a palladium–diimine complex. The developed catalyst exhibited the highest turnover number reported to date for the direct arylation of benzene due to increased stability provided by the diimine ligand. The reaction was also performed using only 2–3 equiv of simple arenes. Mechanistic studies in combination with kinetic measurements, isotope effect experiments, synthesis of possible intermediates, and stoichiometric reactions suggested that this reaction follows a cooperative bimetallic mechanism.

Living Polymerization of Ethylene and Copolymerization of Ethylene/Methyl Acrylate Using “Sandwich” Diimine Palladium Catalysts

Cationic Pd(II) catalysts incorporating bulky 8-p-tolylnaphthyl substituted diimine ligands have been synthesized and investigated for ethylene polymerization and ethylene/methyl acrylate copolymerization. Homopolymerization of ethylene at room temperature resulted in branched polyethylene with narrow Mw/Mn values (ca. 1.1), indicative of a living polymerization. A mechanistic study revealed that the catalyst resting state was an alkyl olefin complex and that the turnover-limiting step was migratory insertion, thus the turnover frequency is independent of ethylene concentration. Copolymerization of ethylene and methyl acrylate (MA) was also achieved. MA incorporation was found to increase linearly with MA concentration, and copolymers with up to 14 mol % MA were prepared. Mechanistic studies revealed that acrylate insertion into a Pd–CH3 bond occurs at −70 °C to yield a four-membered chelate, which isomerizes first to a five-membered chelate and then to a six-membered chelate. Barriers to migratory insertion of both the (diimine)PdCH3(C2H4)+ (19.2 kcal/mol) and (diimine)PdCH3(η2-C2H3CO2Me)+ (15.2 kcal/mol) were measured by low-temperature NMR kinetics.

Cytotoxicity of Diimine Palladium (II) Complexes of Alkyldithiocarbamate Derivatives on Human Lung, Ovary and Liver Cells.

Three new Complexes of formula [pd(bpy)(R-NH-CSS)] Cl (where bpy is 2/2'- bipyridine, and R-NH-CSS is butylamine, hexylamine- and octyamine-dithiocabamate anion) have been synthesized by University of Sistan and Blachostan. These complexes have been characterized by spectroscopic methods such as ultraviolet-visible, infrared and (1)H-NMR as well as conductivity measurements and chemical analysis. In these complexes, each of the dithiocarbamate ligands coordinates to Pd (II) center as bidentate with two sulfur atoms. We have found a 1:1 electrolyte in water conductivity test for the above mentioned compounds. To measure the biologic activity and potential anticancer efficacy of these compounds, they have been compared with cisplatin and its palladium analogue of [Pd (NH3)2 Cl2] on three different cell lines of human hepatocarcinoma HepG2, human ovarian carcinoma OV2008, and human lung adenocarcinoma A549. Clonogenic assay has shown LD50s in the range of 0.131±0.025 to 0.934 ± 0.194 for these compounds on above cell lines. In comparison, cisplatin has shown LD50s of 0.838 ± 0.074, 2.196 ± 0.220, and 2.799 ± 0.733 on OV2008, HepG2 and A549 cell lines, respectively. As a conclusion, above three new complexes have shown higher cytotoxicities compared to cisplatin on three different human cell lines. Based on biological tests, these compounds may potentially be considered as good anticancer candidates for further pharmacological studies.

Cover Picture: (Adv. Synth. Catal. 9/2009)

AbstractThe cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to β‐agostic complexes in which palladium can rapidly migrate along the chain (“chain‐walking”) through β‐elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches‐on‐branches since chain‐walking through tertiary centers is facile.magnified image

Cover Picture: (Adv. Synth. Catal. 7‐8/2009)

AbstractThe cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to β‐agostic complexes in which palladium can rapidly migrate along the chain (“chain‐walking”) through β‐elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches‐on‐branches since chain‐walking through tertiary centers is facile.magnified image

Cover Picture: (Adv. Synth. Catal. 6/2009)

AbstractThe cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to β‐agostic complexes in which palladium can rapidly migrate along the chain (“chain‐walking”) through β‐elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches‐on‐branches since chain‐walking through tertiary centers is facile.magnified image

Cover Picture: (Adv. Synth. Catal. 5/2009)

AbstractThe cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to β‐agostic complexes in which palladium can rapidly migrate along the chain (“chain‐walking”) through β‐elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches‐on‐branches since chain‐walking through tertiary centers is facile.magnified image

Cover Picture: (Adv. Synth. Catal. 4/2009)

AbstractThe cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to β‐agostic complexes in which palladium can rapidly migrate along the chain (“chain‐walking”) through β‐elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches‐on‐branches since chain‐walking through tertiary centers is facile.magnified image

Cover Picture: (Adv. Synth. Catal. 3/2009)

AbstractThe cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to β‐agostic complexes in which palladium can rapidly migrate along the chain (“chain‐walking”) through β‐elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches‐on‐branches since chain‐walking through tertiary centers is facile.magnified image

Unconjugated diimine palladium complexes as Heck coupling catalysts

Four unconjugated diimine palladium complexes have been synthesized, and spectroscopically and structurally characterized. All four palladium complexes were used as catalysts in the Heck coupling reaction between iodobenzene and methyl acrylate or butyl acrylate with very good conversion to either methyl (2 E)-3-phenylacrylate or butyl (2 E)-3-phenylacrylate.

Methacrylate Insertion into Cationic Diimine Palladium(II)−Alkyl Complexes and the Synthesis of Poly(alkene-block-alkene/carbon monoxide) Copolymers

The reaction of cationic Pd(II) diimine complex [(N∧N)Pd(Me)(L)][B(Arf)4] ((N∧N) = 2,3-bis(2,6-di-isopropylphenylimino)butane, Arf = 3,5-(CF3)2C6H3, L = Et2O) with methyl methacrylate results in 1,...

Synthesis and Structural Studies of NCN Diimine Palladium Pincer Complexes Bearing m-Terphenyl Scaffolds

The reaction of 2,6-[2-{RN=C(H)}C(6)H(4)](2)C(6)H(3)I [R = Ph (4), Cy (5), 2,6-Me(2)C(6)H(3) (6), 2,4,6-Me(3)C(6)H(2) (7), (S)-alpha-methylbenzyl (8)] with Pd(2)(dba)(3) afforded the NCN diimine pincer palladium complexes [2,6-[2-{RN=C(H)}C(6)H(4)](2)C(6)H(3)PdI] (9-13) by oxidative addition of the C-I bonds of the ligand precursors. Single-crystal X-ray diffraction analyses of complexes 9-13 reveal formal C(2)-symmetric environments. Variable-temperature NMR studies of complexes 11 and 12 show hindered rotation about the N-Ar bonds and also suggest that atropisomers of complexes 9-13 do not interconvert on the NMR time scale. Consistent with this proposal, isolation of the two possible isomers of 13 (13a and 13b) was possible, and their structures and NMR properties have been examined in detail.

Mechanistic Studies of Catalytic Polyethylene Chain Growth in the Presence of Water

Position blocked? Quantitative studies of polyethylene chain growth in the presence of water by variable-temperature (VT) 1H NMR spectroscopy show, unexpectedly, that water can compete with monomer binding at the vacant coordination site in cationic diimine palladium(II) methyl as well as higher alkyl complexes (see scheme); the latter are prepared cleanly as water complexes at T<0 °C.