Copper(II) complexes derived from substituted 2,2′-bis-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one) ligands: Synthesis,structure and catalytic activity

New chiral N,N-bidentate 2,2′-bis-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one) ligands have been prepared and characterised by their ¹H and ¹³C NMR spectra and/or optical rotation. The ligands prepared were then tested for their ability to form complexes with copper(II) salts. It was found that the most stable complex is formed from the 2,2′-bis-(4-isopropyl-1,4-dimethyl-4,5-dihydro-1H-imidazol-5-one) ligand and copper(II) chloride. The structure of this complex was determined by means of quantum-chemical computations at the B3LYP or UB3LYP/6-31G(d,p) level. According to the computations, the geometry of the copper atom most resembles a tetrahedral arrangement, which was also confirmed by means of X-ray structural analysis. It was found that the structure of this copper(II) complex does not allow the copper atom to coordinate to additional ligands; therefore, it is catalytically inactive in the asymmetric Henry reaction.     

Tri-component reaction of 2-alkyl-4,5-dichloropyridazin-3(2H)-ones: synthesis of 5-cyano-5-(pyrimidin-2-yl)-2,7-dialkyl-5H-dipyridazino-[4,5-b:4,5-e]-4H-thiopyran-1,6-dione and 2-(4-cyanophenoxy) pyrimidine

Reaction of 2-alkyl-4,5-dichloropyridazin-3(2H)-ones with p-cyanophenol and 2-mercaptopyrimidine in the presence of base gave 2,4,5-trisubstituted-pyridazin-3(2H)-ones 4-9, 2-(4-cyanophenoxy)pyrimidine (10) and 5-cyano-5-(pyrimidin-2-yl)-2,7-dialkyl-5H-dipyridazino[4,5-b:4,5-e]-4H-thiopyran-1,6-diones 11 as a novel heterocycle.     

Syntheses and structures of iron carbonyl complexes derived from N-(5-methyl-2-thienylmethylidene)-2-thiolethylamine and N-(6-methyl-2-pyridylmethylidene)-2-thiolethylamine

The reaction of N-(5-methyl-2-thienylmethylidene)-2-thiolethylamine (1) with Fe₂(CO)₉ in refluxing acetonitrile yielded di-(μ₃-thia)nonacarbonyltriiron (2), μ-[N-(5-methyl-2-thienylmethyl)-η¹:η¹(N);η¹:η¹(S)-2-thiolatoethylamido]hexacarbonyldiiron (3), and N-(5-methyl-2-thienylmethylidene)amine (4). If the reaction was carried out at 45 °C, di-μ-[N-(5-methyl-2-thienylmethylidene)-η¹(N);η¹(S)-2-thiolethylamino]-μ-carbonyl-tetracarbonyldiiron (5) and trace amount of 4 were obtained. Stirring 5 in refluxing acetonitrile led to the thermal decomposition of 5, and ligand 1 was recovered quantitatively. However, in the presence of excess amount of Fe₂(CO)₉ in refluxing acetonitrile, complex 5 was converted into 2-4. On the other hand, the reaction of N-(6-methyl-2-pyridylmethylidene)-2-thiolethylamine (6) with Fe₂(CO)₉ in refluxing acetonitrile produced 2, μ-[N-(6-methyl-2-pyridylmethyl)-η¹ (N_py);η¹:η¹(N); η¹:η¹(S)-2-thiolatoethylamido]pentacarbonyldiiron (7), and μ-[N-(6-methyl-2-pyridylmethylidene)-η²(C,N);η¹:η¹(S)-2- thiolethylamino]hexacarbonyldiiron (8). Reactions of both complex 7 and 8 with NOBF₄ gave μ-[(6-methyl-2-pyridylmethyl)-η¹(N_py);η¹:η¹(N);η¹:η¹(S)-2-thiolatoethylamido](acetonitrile)tricarbonylnitrosyldiiron (9). These reaction products were well characterized spectrally. The molecular structures of complexes 3, 7-9 have been determined by means of X-ray diffraction. Intramolecular 1,5-hydrogen shift from the thiol to the methine carbon was observed in complexes 3, 7, and 9.     

Copper(I) complexes of N-(aryl)pyridine-2-aldimines: Spectral, electrochemical and catalytic properties

The reactions of N-(aryl)pyridine-2-aldimines (L-R; R = OCH₃, CH₃, H, Cl and NO₂), derived from pyridine-2-aldehyde and para-substituted anilines, with CuI in methanol under ambient conditions afford a series of brown complexes of the type [{Cu(L-R)I}₂]. The structure of the [{Cu(L-OCH₃)I}₂] complex has been determined by X-ray crystallography. In these dimeric complexes the two copper centers are linked through an iodo-bridge, and the L-R ligands are coordinated to the metal center through the pyridine-nitrogen and imine-nitrogen. All the complexes show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. These complexes also show an emission near 465 nm, whilst they are excited at 340 nm, with relatively poor quantum yields (φ ∼0.002 at 298 K). Cyclic voltammetry on all the complexes shows two successive Cu(I)-Cu(II) oxidations on the positive side of SCE, and a reduction of the coordinated imine ligand on the negative side. These copper(I) complexes are found to efficiently catalyze Suzuki type C-C coupling reactions.     

Dinuclear copper(II) perchlorate complexes with 6-(benzylamino)purine derivatives: Synthesis,X-ray structure,magnetism and antiradical activity

The reactions of Cu(ClO₄)₂·6H₂O with 6-(benzylamino)purine derivatives in a stoichiometric 1:2 metal-to-ligand ratio led to the formation of penta-coordinated dinuclear complexes of the formula [Cu₂(μ-L^1–8)₄(ClO₄)₂](ClO₄)₂·nsolv, where L¹ = 6-(2-fluorobenzylamino)purine (complex 1), L² = 6-(3-fluorobenzylamino)purine (2), L³ = 6-(4-fluorobenzylamino)purine (3), L⁴ = 6-(2-chlorobenzylamino)purine (4), L⁵ = 6-(3-chlorobenzylamino)purine (5), L⁶ = 6-(4-chlorobenzylamino)purine (6), L⁷ = 6-(3-methoxybenzylamino)purine (7) and L⁸ = 6-(4-methoxybenzylamino)purine (8); n = 0–4 and solv = H₂O, EtOH or MeOH. All the complexes have been fully characterized by elemental analysis, FTIR, UV–Vis and EPR spectroscopy, and by magnetic and conductivity measurements. Variable temperature (80–300 K) magnetic susceptibility data of 1–8 showed the presence of a strong antiferromagnetic exchange interaction between two Cu(II) (S = 1/2) atoms with J ranging from −150.0(1) to −160.3(2) cm⁻¹. The compound 6·4EtOH·H₂O was structurally characterized by single crystal X-ray analysis. The Cu?Cu separation has been found to be 2.9092(8) Å. The antiradical activity of the prepared compounds was tested by in vitro SOD-mimic assay with IC₅₀ in the range 8.67–41.45 μM. The results of an in vivo antidiabetic activity assay were inconclusive and the glycaemia in pre-treated animals did not differ significantly from the positive control.     

Synthesis,structure and biological properties of several binary and ternary complexes of copper(II) with ciprofloxacin and 1,10 phenanthroline

In this study, a new binary complex [Cu(HCip)₂](NO₃)₂ · 6H₂O (1) has been synthesized and then characterized by X-ray structure analyses. In this compound, each ciprofloxacin acts as a bidentate ligand resulting in a crystallographically planar configuration; the nitrate anions are located in apical positions with an axial distance significantly larger than the equatorial distances, which would be consistent with a very weak metal ion interaction due to the Jahn–Teller effect. In addition, both the synthesis and characterization of two new ternary complexes of ciprofloxacin–copper(II)–1,10-phenanthroline, [Cu(phen)(Cip)](NO₃) · 4H₂O (2) and Cu(phen)(HCip)(NO₃)₂ · H₂O (3), have been accomplished. We have also undertaken the single crystal structural determination of 2, in which the ciprofloxacin acts as tridentate bridging ligand; the complex exhibits a five-coordinated motif in a distorted square pyramidal environment around the metal center. The chemical nuclease activity of compounds 2 and 3 has also been studied, revealing that both compounds behave as efficient chemical nucleases in the presence of ascorbate. Mechanistic studies, with various radical oxygen scavengers, indicate that the DNA cleavage reaction is mediated by hydroxyl radicals, singlet oxygen, and the superoxide anion.     

Synthesis, stereochemical and conformational properties of trans-2,3-dihydro-2-methyl-3-(1,2,4-triazolyl)-4H-1-benzopyran-4-one oxime ethers

A convenient synthesis and structural characterization of (Z)- and (E)-trans-2,3-dihydro-2-methyl-3-(1,2,4-triazolyl)-4H-1-benzopyran-4-one oxime ethers has been achieved. By analysis of vicinal interproton coupling constants, it is believed that trans-2,3-dihydro-2-methyl-3-(1,2,4-triazolyl)-4H-1-benzopyran-4-ones which exist predominantly in the diequatorial half-chair or sofa conformation was found to exist predominantly in the diaxial orientation upon conversion to the corresponding oxime ether derivatives.     

Synthesis and characterization of 9-methyl-2-morpholin-4-yl-8-substituted phenyl-1H-purine derivatives using polyphosphoric acid (PPA) as an efficient catalyst

We demonstrate the synthesis of various purine derivatives through the coupling of N⁴-methyl-2-morpholin-4-yl-pyrimidine-4,5-diamine with various aldehydes by using polyphosphoric acid (PPA) as an efficient catalyst in DMF at reflux temperature. The PPA catalyst gave better yields (70-85%) in short reaction times (45-60 min). This commercially available cheap catalyst is more active than many reported expensive catalysts. Many aldehydes underwent the above conversion to form a series of 9-methyl-2-morpholin-4-yl-8-phenyl-9H-purines.     

Copper(II) complexes containing chiral substituted 2-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridine ligands: Synthesis, X-ray structural studies and asymmetric catalysis

New chiral N,N-bidentate ligands derived from substituted 2-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridines have been prepared and characterised by means of ¹H, ¹³C NMR spectroscopy and optical rotation. Their Cu(II) complexes were characterized by means of elemental analysis, ¹H NMR spectroscopy and MS. By means of X-ray diffraction, molecular geometry of the complex of 2-(1-methyl-4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridine with copper(II) chloride was determined. The complex exhibits heterochiral dimeric arrangement of two square pyramids with one terminal and one bridge-forming chlorine atoms and two nitrogen atoms in the bases of the pyramids. The tops of these pyramids are formed by the remaining chlorine atoms. The complexes prepared catalyse the Henry reaction with the overall yields of 41-97% and with the maximum enantioselective excess of 19%.     

Synthesis of 1H-pyrrolo[3,2-c]quinoline derivatives via palladium-catalyzed heteroannulation of 2-aryl-3-iodo-4-(phenylamino)quinolines and 4-(N,N-allylphenylamino)-2-aryl-3-iodoquinolines

Palladium(0)/copper iodide catalyzed Sonogashira cross-coupling of 2-aryl-3-iodo-4-(phenylamino)quinolines with terminal alkynes afforded series of 1,2,4-trisubstituted 1H-pyrrolo[3,2-c]quinolines in a single-step operation. Conversely, the 4-(N,N-allylphenylamino)-2-aryl-3-iodoquinoline derivatives were found to undergo PdCl₂(PPh₃)₂/CuI catalyzed intramolecular Heck reaction to yield the corresponding 1,3,4-trisubstituted 1H-pyrrolo[3,2-c]quinolines.     

Synthesis,structure, electrochemical properties,and antioxidant activities of copper(II) and zinc(II) complexes with N,N-bis(N-ethyl-2-ylmethylbenzimidazol)allylamine ligand

N,N-bis(N-methyl-2-ylmethylbenzimidazole)aniline (EtAIDB) and its transition metal complexes, [Cu(EtAIDB)Br₂]·EtOH {dibromo[N,N-bis(N-methyl-2-ylmethylbenzimidazole)aniline] copper(II) ethanol} (1) and [Zn(EtAIDB)Br₂] {dibromo[N,N-bis(N-methyl-2-ylmethylbenzimidazole)aniline] zinc(II)} (2), have been synthesized and characterized by elemental analysis, molar conductivity, UV–visible, and IR spectroscopy. The X-ray crystallographic studies of 1 and 2 have shown two different arrangements: 1 is distorted square-based pyramidal, while 2 can be treated as distorted tetrahedral. The cyclic voltammogram of 1 represents quasi-reversible Cu²⁺/Cu⁺ pairs. In vitro antioxidant tests showed that 1 had significant antioxidant activity against superoxide and hydroxy radicals.     

Thermal studies on cobalt(II), nickel(II) and copper(II) ternary complexes of N-(2-acetamido) iminodiacetic acid and imidazoles

The thermal decomposition of Co(II), Ni(II) and Cu(II) complexes has been studied using thermogravimetry (TG) and differential TG (DTG). The complexes have been characterized by IR spectroscopy. The results reveal that the decomposition of these complexes is accompanied by the formation of metal acetate as an intermediate fragments. On the basis of the applicability of a non-isothermal kinetic equations, it was demonstrated that the stability of the complexes follows the order Co(II)>Cu(II)>Ni(II). These stably correspond to the strength of chelation between the metal ions and the primary and secondary ligands. A possible mechanism of the thermal decomposition of the complexes is suggested.     

Synthesis of 1-benzyl-8,9-dihydroimidazo[4,5-c]pyrrolo[3,2-g]quinolin-4(5H)-one via palladium-catalyzed intramolecular arylation

The synthesis of a novel tetracyclic structure, 8,9-dihydroimidazo[4,5-c]pyrrolo[3,2-g]quinolin-4(5H)-one, has been achieved by a convergent pathway. Coupling of the weakly nucleophilic hindered aromatic amine with 1-benzylimidazole-4-carboxylic acid, 7, afforded the corresponding amide 9 using a DCP/DMF complex; subsequent Heck-type arylation leading to desired tetracyclic molecule imidazo[4,5-c]-pyrrolo[3,2-g]quinolin-4(5H)-one.     

Convenient synthesis of 3-fluoro-4,5-diphenylfuran-2(5H)-one from benzoin ethers : Novel and efficient Z-E isomerisation and cyclisation of 2-fluoroalkenoate precursors, substitution of vinylic fluorine

Mixtures of ethyl (E)- and (Z)-4-alkoxy-2-fluoro-3,4-diphenylbut-2-enoates (6-8) prepared from benzoin ethers and ethyl 2-(diethoxyphosphoryl)-2-fluoroacetate were transformed in high yields to the target 3-fluoro-4,5-diphenylfuran-2(5H)-one (14) using bromine in tetrachloromethane at room temperature. The non-cyclisable Z-isomers 6b-8b were gradually isomerised to the cyclisable E-isomers 6a-8a during the process. The reaction of the (E)-butenoates 6a-8a with boron trifluoride led to furanone 14, while in Z-isomers 6b-8b both alkoxy group and vinylic fluorine were substituted with bromine during the reaction. Mechanisms for both complex reactions have been proposed. Furanone 14 was transformed to 2-[tert-butyl(dimethyl)silyloxy]-3-fluoro-4,5-diphenylfuran (18) as a novel building block.     

Chemoselective synthesis of 3H-pyrrolo[2,3-c]quinolin-4(5H)-one derivatives from 3-phenacylideneoxindoles and substituted tosylmethyl isocyanide (TosMIC)

A simple and convenient synthetic approach to access of 3H-pyrrolo[2,3-c]quinolin-4(5H)-one derivatives by the reaction of (Z)-3-(2-oxo-2-ethylidene)indolin-2-one derivatives 1 with functionalized TosMICs under basic conditions has been reported. The desired products were obtained in good to excellent yields (82–94%). The easy accessibility of the starting materials, simple and mild reaction conditions, short reaction time, and good to excellent chemical yields make this methodology highly efficient.     

Synthesis of substituted 3-(3-chloro-1H-pyrazol-5-yl)quinoxalin-2(1H)ones

Synthetic strategies to gain access to all four isomers of 3-(3-chloro-1H-pyrazol-5-yl)quinoxalin-2(1H)ones with monosubstituted benzo core (i.e., compounds 8a–d) are described. Preparation of these heterocyclic compounds succeeded starting from only two different substituted 2-nitroanilines (i.e., 3-methoxy- and 4-methoxy-2-nitroaniline) in three or five steps, respectively.     

Synthesis and properties of novel 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: methodology for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates

Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac₂O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The ¹³C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG^‡) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03 kcal mol⁻¹ by the variable temperature ¹H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF₄⁻ and 12a-c·BF₄⁻) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF₄⁻) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF₄/Ac₂O afforded two kinds of novel products 11a-c·BF₄⁻ and 12a,c·BF₄⁻ in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF₄⁻ and 12a-c·BF₄⁻ observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF₄⁻ and 12a-c·BF₄⁻ were studied, and structural characterization of 11c·BF₄⁻ based on the X-ray crystal analysis and MO calculation was also performed.     

Iron(II) and cobalt(II) complexes bearing N-((pyridin-2-yl)methylene)-quinolin-8-amine derivatives: Synthesis and application to ethylene oligomerization

A series of tridentate NˆNˆN iron(II) and cobalt(II) complexes containing N-((pyridin-2-yl)methylene)-quinolin-8-amine derivatives were synthesized and characterized by elemental and spectroscopic analyses. The molecular structure of 1a was confirmed by X-ray diffraction analyses. On treatment with modified methylaluminoxane, these metal complexes exhibited good catalytic activities up to 2.8 × 10⁶ g mol⁻¹(Fe) h⁻¹ for ethylene oligomerization, and butenes were the major products with nice selectivity for 1-C₄. The steric and electronic effects on catalytic activities of metal complexes were carefully investigated as well as the influence of various reaction parameters. In the catalytic system, Fe(II) complexes performed better catalytic activities than their Co(II) analogues. With ligands having bulky substituents, the better catalytic activity was observed in catalytic system of Fe(II) complex, however, the lower catalytic activity was obtained in catalytic system of Co(II) complexes.     

X-ray structure and multinuclear NMR studies of platinum(II) complexes with 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one

New dichloride platinum(II) complexes with 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one (HmtpO) have been synthesized and characterized by thermal analysis, infrared and ¹H, ¹³C, ¹⁵N, ¹⁹⁵Pt NMR spectroscopy. X-ray crystal structures of cis-PtCl₂(NH₃)(HmtpO) (1) and cis-PtCl₂(HmtpO)₂ · 4H₂O (2b) were determined to R = 0.0332 and R = 0.0802, respectively. In both complexes the Pt(II) ions have a square-planar geometry with two adjacent corners being occupied by two nitrogens of HmtpO molecules for 2b or NH₃ and HmtpO molecules for 1, whereas the remaining adjacent corners are occupied by two chloride anions. Spectroscopic data confirm the square planar geometry with N(3) bonded HmtpO, S-bonded dimethylsulfoxide and two trans chloride anions for trans-PtCl₂(dmso) · 4H₂O (3).