Synthesis and catalytic properties of cationic palladium(II) and rhodium(I) complexes bearing diphosphinidinecyclobutene ligands

Cationic palladium(II) and rhodium(I) complexes bearing 1,2-diaryl-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutene ligands (DPCB–Y) were prepared and their structures and catalytic activity were examined (aryl = phenyl (DPCB), 4-methoxyphenyl (DPCB–OMe), 4-(trifluoromethyl)phenyl (DPCB–CF₃)). The palladium complexes [Pd(MeCN)₂(DPCB–Y)]X₂ (X = OTf, BF₄, BAr₄ (Ar = 3,5-bis(trifluoromethyl)phenyl)) were prepared by the reactions of DPCB–Y with [Pd(MeCN)₄]X₂, which were generated from Pd(OAc)₂ and HX in MeCN. On the other hand, the rhodium complexes [Rh(MeCN)₂(DPCB–Y)]OTf were prepared by the treatment of [Rh(μ-Cl)(cyclooctene)₂]₂ with DPCB–Y in CH₂Cl₂, followed by treatment with AgOTf in the presence of MeCN. The cationic complexes catalyzed conjugate addition of benzyl carbamate to α,β-unsaturated ketones.     

Studies of thermal decomposition of palladium(II) complexes with olefin ligands

Thermal decomposition kinetics of ML₂ (M = Ni(II) and Co(II); L = 5-(2-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)hydrazono)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione) complexes were investigated by thermogravimetric analysis (TGA). The first decomposition process of the NiL₂ and CoL₂ complexes occurs in the temperature range of 320–350 °C. Kinetics parameters corresponding to this step, such as activation energy, E_α, and apparent pre-exponential factor, ln A_aap, were calculated from the thermogravimetric data at the heating rates of 5, 10, 15 and 20 K min⁻¹ by differential (Friedman's equation) and integral (Flynn–Wall–Ozawa's equation) methods. The results show that the activation energy evidently depends on the extent of conversion. As far as their activation energy is concerned, NiL₂ complex shows a higher thermal stability than the CoL₂ complex.     

Synthesis, X-ray structures, and catalytic applications of palladium(II) complexes bearing N-heterocyclic iminocarbene ligands

Two new Pd(II) N-heterocyclic iminocarbene complexes (C-N)PdCl₂ that contain 5-membered chelate rings have been prepared by carbene transfer from a silver iminocarbene precursor to (COD)PdCl₂. The new Pd imonocarbene complexes, as well as two that have been previously reported (altogether three 5-membered and one 6-membered chelate ring complexes) have been evaluated as catalysts for the Suzuki-Miyaura coupling reaction. The complexes were found to be active in the reaction, but without exceptional catalytic performances. The 5-membered chelate ring complexes appeared to be more robust and remained active for a longer time than the 6-membered ring congener. The catalytic performance of the 5-membered chelate ring complexes appeared to be rather insensitive to the steric demands of the imine-N-aryl group. The X-ray structure of one of the Ag iminocarbene complexes reveals the κ¹(C) bonding of the iminocarbene moiety in a nearly linear Ag(I) complex; two monomeric units are associated through a weak Ag-Ag interaction. The X-ray structures of two new Pd iminocarbene complexes (C-N)PdCl₂ confirm the chelating κ²(C,N) nature of the iminocarbene moiety; in both complexes, the Pd-Cl distances trans to carbene-C are slightly longer than those trans to imine-N.     

Hindered diarylether and diarylsulfone bisphosphine ligands: atropisomerism and palladium complexes

Phosphines and bisphosphines derived from hindered ortho-substituted diaryl ethers and diarylsulfones by lithiation are, with appropriate substitution patterns, resolvable atropisomeric ligands which form crystalline complexes with palladium dichloride.     

Synthesis,structure and olefin polymerization catalysis of nickel(II) complexes bearing N,O-chelate ligands

Four β-ketoimine ligands (two series) were prepared through traditional condensation reactions of β-diketones with 2,6-substituted anilines. Reaction took place only at the cyclohexanone carbonyl rather than at the acetyl or benzoyl carbonyl, even if more than two equivalents of the amines were added. Consequently, four new moisture- and air-stable bis(β-ketoamino)nickel(II) complexes, Ni[2–CH₃C(O)C₆H₈(=NAr)]₂ (Ar?=?2, 6-iPr₂C₆H₃, (1); Ar?=?2, 6-Me₂C₆H₃, (2) and Ni[2–PhC(O)C₆H₈(=NAr)]₂ (Ar?=?2, 6-iPr₂C₆H₃, (3); Ar?=?2, 6-Me₂C₆H₃, (4) were obtained and characterized. The solid-state structures of complex 1, 2 and 3 have been determined by single-crystal X-ray diffraction. Additionally, these complexes can be applied as highly active catalyst precursors for vinyl polymerization of norbornene (NBE) after activation with methylaluminoxane (MAO).     

Platinum(II) and palladium(II) complexes with substituted pyrimidines

Summary Platinum(II) and Palladium(II) complexes with 2-mercaptopyrimidine, 2-thiocytosine (4-aminopyrimidine 2-thione), and isocytosine (2-amino-4-hydroxy pyrimidine) were prepared and characterised by elemental analysis, conductivity data, i.r.,¹H n.m.r. and¹³C n.M.r. spectral studies. 2-Mercaptopyrimidine and 2-thiocytosine are coordinated to the metal ion through N(3) and C₂S, thus forming a four-membered chelate ring. Isocytosine acts as a monodentate ligand and coordinates to the metal ion through N(1). All the complexes are non-electrolytes.     

Dual chirality control of palladium(II) complexes bearing tropos biphenyl diamine ligands

Axial and center chirality of Pd complexes with tropos biphenyl secondary diamine ligands is shown to be controlled by chiral amide (R)-DABNTf, which can efficiently discriminate between two enantiomeric Pd complexes.     

Structural variation, dynamics, and catalytic application of palladium(II) complexes of di-N-heterocyclic carbene-amine ligands

A series of palladium(II) complexes incorporating di-NHC-amine ligands has been prepared and their structural, dynamic and catalytic behaviour investigated. The complexes [trans-(kappa(2)-(tBu)CN(Bn)C(tBu))PdCl(2)] (12) and [trans-(kappa(2)-(Mes)CN(H)C(Mes))PdCl(2)] (13) do not exhibit interaction between the amine nitrogen and palladium atom respectively. NMR spectroscopy between -40 and 25 degrees C shows that the di-NHC-amine ligand is flexible expressing C(s) symmetry and for 13 rotation of the mesityl groups is prevented. In the related C(1) complex [(kappa(3)-(tBu)CN(H)C(tBu))PdCl][Cl] (14) coordination of NHC moieties and amine nitrogen atom is observed between -40 and 25 degrees C. Reaction between 12-14 and two equivalents of AgBF(4) in acetonitrile gives the analogous complexes [trans-(kappa(2)-(tBu)CN(Bn)C(tBu))Pd(MeCN)(2)][BF(4)](2) (15), [trans-(kappa(2)-(Mes)CN(H)C(Mes))Pd(MeCN)(2)][BF(4)](2) (16) and [(kappa(3)-(tBu)CN(H)C(tBu))Pd(MeCN)][BF(4)](2) (17) indicating that ligand structure determines amine coordination. The single crystal X-ray structures of 12, 17 and two ligand imidazolium salt precursors (tBu)C(H)N(Bn)C(H)(tBu)][Cl](2) (2) and [(tBu)C(H)N(H)C(H)(tBu)][BPh(4)](2) (4) have been determined. Complexes 12-14 and 15-17 have been shown to be active precatalysts for Heck and hydroamination reactions respectively.     

Synthesis, characterization and catalytic activity of three palladium(II) complexes containing Schiff base ligands

Three new Pd(II) complexes of Schiff base ligands, namely, [Pd₄(L¹)₄] (1), [Pd₂(L²)₂Cl₂] (2) and [Pd(L³)₂Cl₂] (3) [HL ¹ ?=?N-(benzylidene)-2-aminophenol; L ² ?=?N-(2,4-dichlorobenzylidene)-2,6-diethylbenzenamine, L ³ ?=?4-(2,4-dichlorobenzylide-neamino)phenol] have been synthesized using solvothermal methods and characterized by elemental analysis, spectroscopy and single crystal X-ray diffraction. The crystal structures of the free ligands were also determined. The ??-oxygen-bridged tetranuclear cyclometallated Pd(II) complex (1) contains four nearly planar units, in which Pd^II is four-coordinate. Complex 2 is a ??-chloro-bridged dinuclear cyclometallated Pd(II) complex, whereas complex 3 is mononuclear. The Heck reactions of bromobenzene with acrylic acid catalyzed by complexes 1?C3 have also been studied.     

Synthesis and characterization of nickel(II) maltolate complexes containing ancillary bisphosphine ligands

Cationic nickel(II) complexes containing chelating O,O′-donor maltolate or ethyl maltolate ligands in conjunction with bidentate bisphosphine ligands Ph₂P(CH₂) _n PPh₂ were prepared by a one-pot reaction starting from nickel(II) acetate, bisphosphine, maltol (or ethyl maltol), and trimethylamine, and isolated as their tetraphenylborate salts. An X-ray structure determination of [Ni(maltolate)(Ph₂PCH₂CH₂PPh₂)]BPh₄ shows that the maltolate ligand binds asymmetrically to the (slightly distorted) square-planar nickel(II) center. The simplicity of the synthetic method was extended to the synthesis of the known platinum(II) maltolate complex [Pt(maltolate)(PPh₃)₂]BPh₄ which was obtained in high purity.     

New palladium(II) complexes with pyrazole ligands

The pyrazole ligand 3,5-dimethyl-4-iodopyrazole (HdmIPz) has been used to obtain a series of palladium(II) complexes (1–4) of the type [PdX₂(HdmIPz)₂] {X = Cl⁻ (1); Br⁻ (2); I⁻ (3); SCN⁻ (4)}. All compounds have been isolated, purified, and characterized by means of elemental analysis, IR spectroscopy, ¹H and ¹³C{¹H}-NMR experiments, differential thermal analysis (DTA), and thermogravimetry (TG). The TG/DTA curves showed that the compounds released ligands in the temperature range 137–605 °C, yielding metallic palladium as final residue. The complexes and the ligand together with cisplatin have been tested in vitro by MTT assay for their cytotoxicity against two murine cancer cell lines: mammary adenocarcinoma (LM3) and lung adenocarcinoma (LP07).     

Cytotoxicity,antioxidant and glutathione S-transferase inhibitory activity of palladium(II) chloride complexes bearing nucleobase ligands

Palladium(II) chloride complexes bearing the nucleobases, adenine, cytosine and guanine, have been synthesized and characterized by UV–vis spectrophotometric methods, magnetic susceptibility, molar conductivity, elemental analysis, FTIR and ¹H-NMR. The complexes were found to have the general composition PdCl₂(NH₃L) (where L = adenine, cytosine or guanine). Square-planar geometry is proposed for these Pd(II) complexes based on magnetic evidence and electronic spectra. The complexes as well as the free nucleobase ligands show varying degrees of cytotoxicity on human promyelocytic leukemia (HL60) and human histiocytic leukemia (U937) cell lines, with cis-[PdCl₂(NH₃)(Gua)] showing IC₅₀ values of 48.03 ± 9.67 and 11.12 ± 3.42 µM against HL60 and U937, respectively. The complexes as well as the ligands did not show anti-proliferative activity against a normal human cell line (NB1RGB). The complexes also show significant antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl radical as well as glutathione S-transferase inhibitory activity.     

New palladium(II) complexes with pyrazole ligands

This study describes the synthesis, IR, ¹H, and ¹³C{¹H} NMR spectroscopic as well the thermal characterization of the new palladium(II) pyrazolyl complexes [PdCl₂(HmPz)₂] 1, [PdBr₂(HmPz)₂] 2, [PdI₂(HmPz)₂] 3, [Pd(SCN)₂(HmPz)₂] 4 {HmPz = 4-methylpyrazole}. The residues of the thermal decomposition were identified as Pd⁰ by X-ray powder diffraction. From the initial decomposition temperatures, the thermal stability of the complexes can be ordered in the sequence: 1 > 2 > 4 ≈ 3. The cytotoxic activities of the complexes and the ligand were investigated against two murine cancer cell lines: mammary adenocarcinoma (LM3) and lung adenocarcinoma (LP07) and compared to cisplatin under the same experimental conditions.     

Two palladium(II) complexes based on Schiff base ligands: synthesis, characterization, luminescence, and catalytic activity

Two Pd(II) complexes involving Schiff base ligands, namely, [Pd(L1)₂] (1), [Pd₂(L₂)Cl₂] (2) [HL1 = 2-((2,6-diisopropylphenylimino)methyl)-4,6-dibromophenol, L2 = N-(4-isopropylbenzylidene)-2,6-diisopropylbenzenamine] have been synthesized using solvothermal methods and characterized by elemental analysis, IR-spectroscopy, thermogravimetric analysis, powder X-ray diffraction, UV–vis absorption spectra, and single-crystal X-ray diffraction. Complex 1 is a mononuclear cyclometalated Pd(II) complex, whereas complex 2 is a μ-chloro-bridged dinuclear. Both 1 and 2 display photoluminescence in the solid state at 298 K and possess fluorescence lifetimes (τ ₁ = 86.40 ns, τ ₂ = 196.21 ns, τ ₃ = 1,923.31 ns at 768 nm for 1, τ ₁ = 69.92 ns, τ ₂ = 136.40 ns, τ ₃ = 1,714.26 ns at 570 nm for 2). The Suzuki reactions of 4-bromotoluene with phenylboronic acid by complexes 1–2 have also been studied.     

Platinum(II) and palladium(II) chlorides complexes with purine,pyrimidine,N-ethylimidazole andN-propylimidazole

Summary Platinum(II) and palladium(II) chloride complexes with purine, pyrimidine (pyrimid),N-ethylimidazole(N-EtIm) andN-propylimidazole(N-PropIm) ligands have been prepared and characterized by analysis and spectroscopic methods. The compounds have general formula M(L₁)(L₂)Cl₂ where M=Pt^II, Pd^II; L₁=purine or pyrimid, L₂=N-EtIm orN-PropIm, except the complexes Pt(purine)(pyrimid)Cl₂ and [Pd(purine)(pyrimid)₂Cl]Cl and [Pt(purine)₂ (N-propIm)Cl]Cl·2H₂O.     

Polymerization of norbornene by palladium(II) complexes bearing ethylene-bridged bisindolinyl- or bis(1,2,3,4-tetrahydroquinolinyl) ligands

Novel moisture and air stable, cationic palladium(II) amine complexes (1–4) of the general type [Pd(N∩N)(X)₂](BF₄)₂, [N∩N=1,2-bis(N-indolinyl)ethane (BIE) 1, 3; 1,2-bis(N-1,2,3,4-tetrahydroquinolinyl)ethane (BTQE) 2, 4; X=NCCH₃, H₂O] were found to catalyze the polymerization reaction of bicyclo[2.2.1]hept-2-ene at room temperature. The amorphous polymer products consist of 2,3-linked norbornene units; no indications for ring opened species could be observed. The polymerization activity of the diaqua-complexes 3, 4 is superior compared to their acetonitrile analogues due to a facile activation by a Wacker-type reaction. The cationic Pd(II)-compounds are inactive towards homo- and copolymerization reactions of polar monomers, like acrylates or carbon monoxide. However, addition of methylacrylate resulted in polynorbornene products with increased molecular weight and narrow molecular weight distributions.     

Azamacrocyclic nickel(II) and copper(II) complexes bearing aryl substituents: synthesis,properties, and crystal structures

A synthetic procedure for preparation of new amphiphilic copper(II) and nickel(II) azamacrocyclic complexes bearing aromatic substituents is developed. The nature of substituents is shown to exert a negligible influence on spectral and electrochemical characteristics of the prepared compounds. The X-ray diffraction analysis of three copper complexes revealed the formation of the dimers of macrocyclic cations associated by noncovalent interactions, nature of which is determined by the structure of the substituent in the macrocyclic ligand.     

Bis(imino)pyridine palladium(II) complexes: Synthesis, structure and catalytic activity

Bis(imino)pyridine palladium(II) complexes 3-6 were synthesized by two different methods. The structure of complexes 3 and 4 has been confirmed by X-ray structure analysis. The catalytic studies show that bis(imino)pyridine palladium(II) complexes are highly efficient catalysts in the Suzuki-Miyaura reaction and the complex 4 was used to catalyze the synthesis of fluorinated liquid crystalline compounds via Suzuki coupling reaction.     

Parent-amido (NH2) palladium(II) complexes: Synthesis,reactions, and catalytic hydroamination

The treatment of [PdL₃(NH₃)](OTf)_n (n = 1; L₃ = (PEt₃)₂(Ph), (2,6-(Cy₂PCH₂)₂C₆H₃), n = 2; L₃ = (dppe)(NH₃)) with NaNH₂ in tetrahydrofuran at ambient temperature or −78 °C afforded the dimeric and monomeric parent-amido palladium(II) complexes anti-[Pd(PEt₃)(Ph)(μ-NH₂)]₂ (1), [Pd(dppe)(μ-NH₂)]₂(OTf)₂ (2), and Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(NH₂) (3), respectively. The molecular structures of the amido-bridged (μ-NH₂) dimeric complexes 1 and 2 were determined by single-crystal X-ray crystallography. The monomeric amido complex 3 reacted with trace amounts of water to give a hydroxo complex, Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(OH) (4). Exposing complex 3 to an excess of water resulted in the complete conversion of the complex into two species [Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(OH₂)]⁺ and [Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(NH₃)]⁺. Complex 3 reacted with diphenyliodonium triflate ([Ph₂I]OTf) to give the aniline complex [Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(NH₂Ph)]OTf. The reaction of 3 with phenylacetylene (HCCPh) yielded a palladium(II) acetylenide Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(CCPh) (5), quantitatively, along with the liberation of ammonia. The reaction of 3 with dialkyl acetylenedicarboxylate yielded diastereospecific palladium(II) vinyl derivatives (Z)-Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(CRCR(NH₂)) (R = CO₂Me (6a), CO₂Et (6b)). The reaction of complexes 6a and 6b with p-nitrophenol produced Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(OC₆H₄-p-NO₂) (7) and cis-CHRCR(NH₂), exclusively. Reactions of 3 with either dialkyl maleate (cis-(CO₂R)CHCH(CO₂R)) (R = CH₃, CH₂CH₃) or cis-stilbene (cis-CHPhCHPh) did not result in any addition product. Instead, isomerization of the cis-isomers to the trans-isomers occurred in the presence of catalytic amounts of 3. Complex 3 reacted with a stoichiometric amount of acrylonitrile (CH₂CHCN) to generate a metastable insertion product, Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(CH(CN)CH₂NH₂). On the other hand, the reaction of 3 with an excess of acrylonitrile slowly produced polymeric species of acrylonitrile. The catalytic hydroamination of olefins with NH₃ was examined in the presence of Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(OTf), producing a range of hydroaminated products of primary, secondary, and tertiary amines with different molar ratios of more than 99% overall yield. A mechanistic feature for the observed catalytic hydroamination is described with regard to the aminated derivatives of palladium(II).     

cis-Fashioned palladium (II) complexes of 2-phenylbenzimidazole ligands: Synthesis, characterization, and catalytic behavior towards Suzuki-Miyaura reaction

Reaction of 2-arylbenzimidazole with PdCl₂(CH₃CN)₂ in CH₂Cl₂ affords benzimidazole palladium (II) complexes in high yields. The structure of complexes C1, C2, and C3 has been confirmed by X-ray structure analysis. The configuration of complexes depends on the substituent on the 2-position of benzimidazole. Phenyl affords the complexes in cis-fashion due to π-π stacking of phenyl and benzimidazole. Tolyl affords the complex in trans-fashion. The catalytic studies show that cis-configured 2-phenylbenzimidazole palladium (II) complexes are highly efficient catalysts in the Suzuki-Miyaura reaction.