A new copper(II) complex as an efficient catalyst of luminol chemiluminescence

A new copper complex (2) has exhibited highly efficient catalytic activity of luminol chemiluminescence in water in the presence of ascorbic acid and dissolved O2 under conditions that conventional catalysts such as Cu(OAc)2, hemin or cyclen-Cu(II) did not show significant activity.     

Unexpected product distributions in the synthesis of 2,6-bis-(indazolyl)pyridine and 2-(pyrazol-1-yl)-6-(indazolyl)pyridine

Reaction of 2-bromopyridine with 2 equiv of sodium indazolide in diglyme at 140 °C affords 2,6-bis-(indazol-1-yl)pyridine and 2-(indazol-1-yl)-6-(indazol-2-yl)pyridine in purified yields of 24% and 68% respectively. A similar reaction, using 1 equiv of sodium indazolide at 70 °C, gives a low-yield mixture of 2-(indazol-1-yl)-6-bromopyridine and 2-(indazol-2-yl)-6-bromopyridine. Both these intermediates are transformed into 2-(pyrazol-1-yl)-6-(indazol-1-yl)pyridine and 2,6-di(pyrazol-1-yl)pyridine upon treatment with 1 equiv of sodium pyrazolide in diglyme at 140 °C. These observations imply that the indazolyl group is a leaving group comparable to a bromo substituent under nucleophilic attack by pyrazolide or indazolide ions under these conditions. No reaction was observed between 2-(pyrazol-1-yl)-6-bromopyridine and 1 equiv of sodium indazolide under the same conditions. A single crystal structure of its iron(II) complex confirmed the regiochemistry of 2,6-bis-(indazol-1-yl)pyridine, and revealed significant conformational flexibility in the distal ligand indazolyl groups.     

A polymer-supported diacetatobis(2-quinolylbenzimidazole)copper(II) complex as an efficient catalyst for oxidation of alcohols with tert-butyl hydroperoxide

A polymer-supported diacetatobis(2-quinolylbenzimidazole)copper(II) complex [PS–(QBIM)₂Cu(II)] was synthesized by functionalization of chloromethylated polystyrene cross-linked with 6.5 % divinyl benzene with 2-(2′-quinolyl)benzimidazole and subsequent treatment with Cu(OAc)₂ in methanol. The complex was characterized by physical, analytical and spectroscopic techniques. Electronic and ESR spectra, together with magnetic susceptibility measurements, indicated that the complex was paramagnetic with distorted octahedral geometry around the copper. The complex was found to be active toward oxidation of various alcohols including phenol, benzyl alcohol and cyclohexanol using 70 % aqueous tert-butyl hydroperoxide under mild conditions. Under the optimized reaction conditions, cyclohexanol gave 100 % conversion to cyclohexanone, benzyl alcohol gave 98 % yield of benzaldehyde and phenol gave 89 % yield of catechol and 4 % of hydroquinone. The complex was recycled five times without much loss in catalytic activity.     

Structural diversity in iron(II) complexes of 2,6-di(pyrazol-1-yl)pyridine and 2,6-di(3-methylpyrazol-1-yl)pyridine

The syntheses, magnetochemistry and crystallography of [Fe(L1)2]I0.5[I3]1.5 (1), [Fe(L1)2][Co(C2B9H11)2]2 (2) and [Fe(L2)2][SbF6]2 (3) (L1 = 2,6-di(pyrazol-1-yl)pyridine; L2 = 2,6-di(3-methylpyrazol-1-yl)pyridine) are described. Compounds 1 and 3 are high-spin between 5-300 K. For 1, this reflects a novel variation of an angular Jahn-Teller distortion at the iron centre, which traps the molecule in its high-spin state. No such distortion is present in 3; rather, the high-spin nature of this compound may reflect ligand conformational strain caused by an intermolecular steric contact in the crystal lattice. Compound 2 exhibits a gradual high --> low spin transition upon cooling with T(1/2) = 318 +/- 3 K, that is only 50% complete. This reflects the presence of two distinct, equally populated iron environments in the solid. One of these unique iron centres adopts the same angular structural distortion shown by 1 and so is trapped in its high-spin state, while the other, which undergoes the spin-crossover, has a more regular coordination geometry. In contrast with 3, the solvated salts [Fe(L2)2][BF4]2 x 4 CH3CN and [Fe(L2)2][ClO4]2 x (CH3)2CO both undergo gradual thermal spin-transitions centred at 175 +/- 3 K.     

A cationic bridged zirconocene complex as the catalyst for the stereospecific polymerization of methyl methacrylate

The cationic bridged zirconocene complex [iPr(Cp)(Ind)Zr(Me)(THF)][BPh₄] ( 1 ‐BPh₄) was synthesized. Polymerization of methyl methacrylate with 1 ‐BPh₄ in CH₂Cl₂ at temperatures between –20 and 20°C led to the formation of isotactic poly(methyl methacrylate). The low polydispersity index of the polymer obtained and a successful two step polymerization of methyl methacrylate with 1 ‐BPh₄ are hints towards a living polymerization mechanism. ¹H and ¹³C NMR analysis revealed an enantiomorphic site‐controlled mechanism for the formation of isotactic poly(methyl methacrylate).     

Basic ionic liquid/FeCl3·6H2O as an efficient catalyst for AGET ATRP of methyl methacrylate

A basic ionic liquid, 1‐butyl‐3‐methyl imidazolium hydroxide ([Bmim]OH), was synthesized and used as the additives in an iron‐mediated atom transfer radical polymerization with activators generated by electron transfer (AGET ATRP) of methyl methacrylate in bulk and solution, using FeCl₃ · 6H₂O as the catalyst, ethyl 2‐bromoisobutyrate as the initiator, vitamin C (Vc) as the reducing agent, and tetrabutylammonium bromide or tetra‐n‐butylphosphonium bromide as the ligand. Catalytic amount of [Bmim]OH could enhance the polymerization rate and produce poly(methyl methacrylate) with controllable molecular weights and narrow molecular weight distributions (M_w/M_n = 1.3–1.4). The nature of controlled/“living” free radical polymerization in the presence of basic ionic liquid was further confirmed by chain‐extension experiments. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

N-allyl-bis(diphenylphosphino)amide nickel dibromide as a catalyst of the polymerization of methyl methacrylate

The polymerization of methyl methacrylate initiated by a catalytic system based on the complex CH₂=CHCH₂N(PPh₂)₂NiBr₂ containing a bidentate phosphine ligand in the coordination sphere of nickel is studied. The activities of this system and of the catalytic system based on NiBr₂(PPh₃)₂ with a monodentate ligand at the nickel atom in the synthesis of PMMA are compared. A scheme of polymerization catalyzed by the CH₂=CHCH₂N(PPh₂)₂)NiBr₂ system is advanced.     

Synthesis and tautomerism of 2-[3(5)-aryl(methyl)pyrazol-4-yl]-1-benzimidazoles

An efficient method has been developed for the synthesis of 2-[3(5)-aryl(methyl)pyrazol-4-yl]-1H-benzimidazoles by cyclocondensation of 2-acylmethyl-1H-benzimidazoles benzoylhydrazones with DMF dimethylacetal. The tautomerism of the compounds obtained via migrations of a proton between the pyrazole nitrogen atoms has been studied by ¹H NMR. The more stable tautomers have electron acceptor aryl substituents placed at position 3 of the pyrazole ring and electron donor aryl substituents or a methyl at position 5. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1370–1377, September, 2006.     

An efficient Pd(II)-(2-aminonicotinaldehyde) complex as complementary catalyst for the Suzuki-Miyaura coupling in water

An efficient new Pd(II)-(2-aminonicotinaldehyde)-catalyzed Suzuki-Miyaura coupling of the aryl halides (Br, Cl and I) and organoboronic acids at moderate temperature in water is described. Low catalyst loading, easy accessibility, being an air-stable catalyst, functional group compatibility, and water as the reaction medium are some of the key features of this synthetic method. This protocol is also applicable for gram scale.     

Hemilability of 2-(1H-imidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands: Imidazole and oxazole ring Lewis basicity,Ni(II)/Pd(II) complex structures and spectra

Fourteen new organic molecules A1–A4, B1–B5, C1–C4 and D and a series of transition metal(II) complexes (Ni1–Ni9 and Pd1–Pd2b) were synthesized and studied in order to characterize the hemilability of 2-(1H-imidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands (A1–A4 = 2-R²-6-(4,5-diphenyl-1R¹-imidazol-2-yl)pyridines, R¹ = H or CH₃, R² = H or CH₃; B1–B5 = 1-R²-2-(pyridin-2-yl)-1R¹-phenanthro[9,10-d]imidazoles/oxazoles, R¹ = H or CH₃, R² = H or CH₃; C1–C4 = 2-(6-R²-pyridin-2-yl)-1H-imidazo/oxazo[4,5-f][1,10]phenanthrolines, R² = H or CH₃; D = 2-mesityl-1H-imidazo[4,5-f][1,10]phenanthroline). They were also used to study the substituent effects on the donor strengths as well as the coordination chemistries of the imidazole/oxazole fragments of the hemilabile ligands.All the observed protonation–deprotonation processes found within pH 1–14 media pertain to the imidazole or oxazole rings rather than the pyridyl Lewis bases. The donor characteristics of the imidazole/oxazole ring can be estimated by spectroscopic methods regardless of the presence of other strong N donor fragments. The oxazoles possessed notably lower donor strengths than the imidazoles. The electron-withdrawing influence and capacity to hinder the azole base donor strength of 4,5-azole substituents were found to be in the order phenanthrenyl (B series) > 4,5-diphenyl (A series) > phenanthrolinyl (C series). An X-ray structure of Ni5b gave evidence for solvent induced ligand reconstitution while the structure of Pd2b provided evidence for solvent induced metal–ligand bond disconnection.Interestingly, alkylation of 1H-imidazoles did not necessarily produce the anticipated push of electron density to the donor nitrogen. Furthermore, substituents on the 4,5-carbons of the azole ring were more important for tuning donor strength of the azole base. DFT calculations were employed to investigate the observed trends. It is believed that the information provided on substituent effects and trends in this family of ligands will be useful in the rational design and synthesis of desired azole-containing chelate ligands, tuning of donor properties and application of this family of ligands in inorganic architectural designs, template-directed coordination polymer preparations, mixed-ligand inorganic self-assemblies, etc.     

Synthesis of poly(methyl methacrylate) in a pyridine solution by atom transfer radical polymerization

Pyridine was used as a solvent for the atom transfer radical polymerization (ATRP) of methyl methacrylate. The homopolymerizations were carried out with methyl 2‐halopropionate (MeXPr, where X was Cl or Br) as an initiator, copper halide (CuX) as a catalyst, and 2,2′‐bipyridine as a ligand from 80 to 120 °C. The mixed halogen system methyl 2‐bromopropionate/copper chloride was also used. For all the initiator systems used, the polymerization reaction showed linear first‐order rate plots, a linear increase in the number‐average molecular weight with conversion, and relatively low polydispersities. In addition, the dependence of the polymerization rate on the temperature is presented. These data are compared with those obtained in bulk, demonstrating the effectiveness of this solvent for this monomer in ATRP. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3443–3450, 2001     

Preparation of a uniform poly(methyl methacrylate) macromonomer and its polymerization

Syndiotactic poly(methyl methacrylate) (st-PMMA) macromonomer having methacryloyl end group was prepared from st-PMMA living anion and separated into uniform macromonomers by means of supercritical fluid chromatography. A uniform macromonomer with the degree of polymerization of 32 was polymerized radically in benzene at 60°C. The uniform dimer, trimer and tetramer of the uniform macromonomer were isolated from the polymerization product by means of gel-permeation chromatography (GPC). The intrinsic viscosity ([η]) in tetrahydrofuran of these uniform comblike polymers was determined by GPC/differential viscometric analysis. The plot of logarithmic [η] against logarithmic molecular weight indicated that the trimer and tetramer assume a little shrinking molecular shape as compared with the unimer and dimer.     

(Butadiene)metallocene/B(C6F5)3 pathway to catalyst systems for stereoselective methyl methacrylate polymerization: evidence for an anion dependent metallocene catalyzed polymerization process

The ansa-zirconocene dichlorides [Me(2)Si(C(5)H(4))(3-R-C(5)H(3))]ZrCl(2) 7a-e (R = H, CH(3), cyclohexyl, -CHMe(2), -CMe(3)) were reacted with butadiene-magnesium to yield the respective (eta(4)-butadiene)metallocenes 17a-e. The chiral examples give a mixture of two s-cis and two s-trans diastereomers. The strong Lewis acid B(C(6)F(5))(3) adds selectively to a terminal butadiene carbon atom to yield the (butadiene)metallocene/B(C(6)F(5))(3) betaine complexes 18a-e. Initially, the formation of the Z-18 isomers is preferred. These consecutively rearrange to the thermodynamically favored isomers E-18. The dipolar systems 18 are active single component metallocene catalysts for the stereospecific polymerization of methyl methacrylate. With increasing steric bulk of the attached single alkyl substituent an increasingly isotactic poly(methyl methacrylate) is obtained. A similar trend is observed in the methyl methacrylate polymerization at the [Me(2)Si(C(5)H(4))(3-R-C(5)H(3))]ZrCH(3)(+) catalysts (9a-e) that were conventionally prepared by methyl abstraction from the corresponding ansa-zirconocene dimethyl complexes by treatment with B(C(6)F(5))(3). A comparison of the poly(methyl methacrylates) obtained at these two series of catalysts has revealed substantial differences in stereoselectivity that probably originate from an influence of the respective counteranions. An initial reactive intermediate of methyl methacrylate addition to the dipolar single component metallocene catalyst E-18a was experimentally observed and characterized by NMR spectroscopy at 253 K. The subsequently formed series of [PMMA-C(4)H(6)(-)B(C(6)F(5))(3)](-) anion oligomers (at the catalyst 18c) was monitored (after quenching) and characterized by electrospray mass spectrometry.     

Polymer‐anchored copper(II) complex: an efficient reusable catalyst for the synthesis of propargylamines

A new, heterogeneous, polymer‐supported copper(II) complex was prepared and characterized using various techniques, including Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X‐ray spectroscopy, atomic absorption spectroscopy and thermogravimetric analysis. This heterogeneous copper catalyst is efficient for the synthesis of propargylamines via a three‐component coupling reaction of aldehydes, amines and alkynes. The effect of solvent on the coupling reactions was investigated. Further, the catalyst can be easily recovered quantitatively by simple filtration and reused for a minimum number of cycles without significant loss of its catalytic activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and Spin State of the Cobalt(II) Complexes with Substituted 2,6-Bis(pyrazol-3-yl)pyridine Ligands

Russian Journal of Coordination Chemistry - The direct template reactions afford the cobalt(II) complexes (I–III) with the hydroxy- and acetyl-substituted 2,6-bis(pyrazol-3-yl)pyridine...     

Living radical polymerization of methyl methacrylate with a zerovalent nickel complex,Ni(PPh3)

A zerovalent nickel complex, Ni(PPh₃)₄, induced living radical polymerization of methyl methacrylate (MMA) in conjunction with an organic bromide as an initiator [R–Br: CCl₃Br, (CH₃)₂C(CO₂Et)Br, (CH₃)₂C(COPh)Br] in the presence of Al(Oi-Pr)₃ additive. The molecular weight distributions were narrow (M̄_w/M̄_n ∼ 1.2) throughout the reactions, and the number-average molecular weights (M̄_n) increased in direct proportion to monomer conversion. In contrast, the polymers obtained with CCl₄ in place of R–Br had broader MWDs (M̄_w/M̄_n > 2). The Al(Oi-Pr)₃ additive should be added for the smooth polymerizations of MMA to occur, similarly to those with a divalent nickel bromide, NiBr₂(PPh₃)₂. The Ni(PPh₃)₄-mediated living polymerization apparently proceeds via the activation of the C Br bond from the initiators R Br, assisted by the redox reaction of the complex between Ni(0) and Ni(I) species. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3003–3009, 1999