Nickel complexes of N,N,N',N'′-tetrakis-(2- benzimidazolylmethyl)-1,2-diaminoethane (L) and the X-ray crystal structure of {[NiL]2+ [NiCl2(H2O)3(C2H5)OH)]}2Cl−(C2H5OH)

The preparation and properties of Ni(II) complexes of the title ligand (L) are described and the X-ray crystal structure of Ni₂LCl₄(H₂O)₃(C₂H₅OH)₂ is reported. The crystal structure shows that the two nickel ions are not bridged but exist as two distinct distorted octahedral species. Six coordination about one nickel ion is produced exclusively by L to give the cationic species [NiL]²⁺. The second nickel ion achieves six coordination through an interesting combination of ligands to produce the novel complex [NiCl₂(H₂O)3 (C₂H₅OH)]. Since the two remaining chloride ions are hydrogen bonded to two of the water molecules and the ethanol molecule of [NiCl₂(H₂O)₃(C₂H₅OH)] the entire complex can be considered to be formed by the cocrystallization of the large cation [NiL]²⁺ by the “large anion” {[NiCl₂(H₂O)₃(C₂H₅OH)]Cl₂}²⁻.     

A 270 MHz 1H-NMR study of three “branched” ribonucleotides A2'p5'U3'p5'g,A2'p5'C3'p5'G and A2'p5'G3'p5'G the importance of being branched with a 2'→5' phosphodiester bond in the pre-mRNA processing reactions (splicing)

Conformational studies with three analogues 3, 4 and 5 of naturally-occurring branched ribonucleotides 1 and 2 have shown that they adopt a secondary structure which is overwhelmingly controlled by a stacking between adenine(2' → 5')nuc1eobase residues while the 3' → 5' linked guanine residue is apart. This observation along with the fact that all four nucleosides can form lariats in nuclear mRNA splicing, but it is guanosine as the 2' → 5' nucleotide that can drive the splicing reaction to completion, suggests a biological significance of the additional 2' → 5' phosphodiester bond formation in the splicing reaction. It is likely that the final implication of formation of such a 2' → 5' linked lariat is that it provides a pathway to assume a free energy minimum conformation through the 2' → 5' stacking, especially in the case of guanosine, to drive the splicing reaction to completion (stacklng-driven-energy-pump).     

A synthetic route to cationic ‘3 + 2’ oxorhenium(V) complexes containing imidazole derivatives

The neutral complex [ReOBr₂(tmi)] [Htmi?=?2-(1-ethanolthiomethyl)-1-methylimidazole] was synthesized by reaction of (n-Bu₄N)[ReOBr₄(OPPh₃)] with an equimolar amount of Htmi in acetonitrile. The ‘3?+?2’ complex [ReO(tmi)(mi)]Cl [Hmi?=?2-(hydroxymethyl)-1-methylimidazole] was isolated from a one-pot reaction of (n-Bu₄N)[ReOCl₄] with Htmi and Hmi in equimolar quantities in acetonitrile. The compounds were characterized by spectroscopic methods and X-ray crystallography. Both complexes have distorted octahedral geometries with the alcoholate oxygen of tmi coordinated trans to the oxo group.     

Introduction of N,N'-disulfonylhydrazines as new sulfonylating reagents for highly efficient synthesis of (E)-β-iodovinyl arenesulfones under mild conditions

N,N'-Disulfonylhydrazines have been proven to be the most reactive precursors of the sulfonyl radicals among all types of sulfonyl substituted hydrazines as early as half a century ago. However, the sulfonyl radicals generated from these compounds have not been used in organic synthesis except the simple self-dimerization synthesis of disulfones controlled by the “solvent-cage-effects”. In this article, N,N′-disulfonylhydrazines were introduced as new sulfonylating reagents and their combinations with NIS were disclosed as new iodosulfonylating reagents of alkynes. Finally, a highly efficient method for the synthesis of (E)-β-iodovinyl arenesulfones was developed by mixing an alkyne, a N,N′-disulfonyl-hydrazine and NIS in aqueous THF at room temperature for 5 min.     

Condensation of 2-alkoxypropenals with N,N- and N,O-1,2-binucleophiles. A route to 2-(1′-alkoxyvinyl)imidazo-lidines and -oxazolidines

Condensation of 2-ethoxypropenal with diaminoethylene in different solvents (CHCl₃, MeCN, H₂O, DMSO) at room temperature gives an equilibrium mixture (1:1–1.5) of tautomeric 2-(1′-ethoxyvinyl)-1,3-imidazolidine and 2-aminoethylimine of 2-ethoxypropenal as well as 1,2-bis(2′-ethoxypropenyl-ideneamino)ethylene. The latter is readily prepared in quantitative yield using a twofold excess of the aldehyde. ¹H NMR was used to demonstrate the effect of heating on the dynamics of the ring-chain tautomeric equilibrium. Reaction of the 2-alkoxypropenals with N-methyl- and N,N′-diphenyl-1,2-diaminoethylenes and with N-phenylaminoethanol gives only the corresponding substituted imidazolidines in 43–95% yield. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov in his 70^th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1809–1815, December, 2008.     

Tricarbonylrhenium(I) complexes with <Emphasis Type="Italic">N,N′</Emphasis>-bis(2- and 4-nitrobenzaldehyde)-1,2-diiminoethane Schiff base ligands: synthesis,spectroscopic and crystal structure studies

fac-[Re(CO)₃(2-nben)Cl] and fac-[Re(CO)₃(4-nbzen)Cl] complexes consisting of 2-nbzen = N,N′-bis(2-nitrobenzaldehyde)-1,2-diiminoethane and 4-nbzen = N,N′-bis(4-nitrobenzaldehyde)-1,2-diiminoethane were synthesized by the reaction of Re(CO)₅Cl with nbzen ligands. These complexes were characterized by physico-chemical, spectroscopic methods and X-ray crystallography. The electrochemical behavior of the two complexes was investigated by cyclic voltammetry. In the crystal structure of [Re(CO)₃(4-nbzen)Cl], the neighbouring molecules are linked together by intermolecular C–H···Cl interactions to form 1D extended chains along the b-axis. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Ruthenium (II) complexes bearing thioether-appended α-iminopyridine ligands: Arene precursors permit access to κ2-N,N and κ3-N,N,S complexes

Herein we report the preparation of a series of Ru(II) complexes featuring α-iminopyridine ligands bearing thioether functionality (NNS^R, where R = Me, CH₂Ph, Ph). Metallation using [(p-cymene)RuCl]₂ permits access to Ru complexes with a κ²-N,N donor set in which the thioether moiety remains uncoordinated. In the presence of a strong field ligand such as acetonitrile or triphenylphosphine, the p-cymene moiety is displaced, and the ligand adopts a κ³-N,N,S binding mode. These complexes are characterized using a combination of solution and solid state methods, including the crystal structure of [(NNS^Me)Ru (NCMe)₂Cl]Cl. The κ²-N,N-Ru(II) complexes are shown to serve as efficient precatalysts for the oxidation of sec-phenethyl alcohol at modest loadings (alcohol: Ru = 20:1), using a variety of external oxidants and solvents. The complex bearing an S-Ph donor was found to be the most active oxidation catalyst of those surveyed, suggesting that the thioether donor plays an active role in the catalytic cycle.     

Rotational energy transfer in the NO A 2Σ+(v&#x27; = 0) state with He and Ar

Rotational energy transfer cross sections are determined for NO (A ²Σ⁺, v' = 0, N' = 0, 7, and 15) +He and NO (A ²Σ⁺, v' = 0, N' = 0) +Ar by the two-color, double-resonance ionization method. Rotational jumps up to ΔN' = 8 take place as a single collision event. The cross sections determined are discussed in terms of the IOS and ECS scaling laws.     

Binuclear iron(III)-iron(III) complexes with the tetradentate Schiff base N,N′-bis(salicylidene)ethylenediamine and dicarboxylic acids or dithiooxamide as bridging ligands

Summary Complexes of the type [(Fe(salen))₂L]·xH₂O (L = glutarate, adipate, pimelate or suberate dianion, x = 0 or L = dithio oxamidate dianion, x = 2) have been prepared and studied by elemental analyses, i.r. and electronic spectra, and magnetic measurements. A dimeric structure with an octahedral arrangement of Fe^III (S = 5/2) is proposed. Some of the complexes have been characterized by temperature-dependent magnetic susceptibilities, but an antiferromagnetic exchange interaction was found only for [(Fe(salen))₂dta]·2H₂O (H₂dta = dithio-oxamide).     

New vanadium and zinc complexes with schiff base ligand N,N′-bis(3-ethoxy-2-hydroxybenzylidene)ethylenediamine: Synthesis,structures, and biochemical properties

The Schiff base ligand N,N′-bis(3-ethoxy-2-hydroxybenzylidene)ethylenediamine (H₂L) reacting with vanadyl acetylacetonate and zinc chloride, respectively, in methanol gave the complexes [VOL] · H₂O (I) and [ZnL(OH₂)] (II). Both complexes were characterized by elemental analyses and IR spectroscopic method in the solid state. Single crystal X-ray analysis was performed, which reveals that both of them are mononuclear complexes. Complex I crystallizes in the monoclinic space group P2₁/c with unit cell dimensions a = 9.4387(7), b = 16.996(1), c = 12.758(1) Å, β = 98.269(2)°, V = 2025.4(3) ų, Z = 4, R ₁ = 0.0365, and wR ₂ = 0.0946. Complex II crystallizes in the tetragonal space group $P\overline {42} _{1m} $ with unit cell dimensions a = b = 22.0489(8), c = 4.9846(4) Å, V = 2423.3(2) ų, Z = 4, R ₁ = 0.0890, and wR ₂ = 0.2278. The V atom in I and the Zn atom in II are in square pyramidal coordination. Anbacterial activities of the Schiff base ligand and the complexes have been studied on the strains B. subtilis, E. coli and S. aureus.     

Silver(I) and mercury(II) complexes with N,N′-bis(acetylacetone)-1R,2R-diaminocyclohexane ligands exhibiting three different coordination modes

Treatment of AgNO₃ with one equiv. of N,N′-bis(acetylacetone)-1R,2R-diaminocyclohexane (L) afforded a mononuclear complex [Ag(η²-L)NO₃] (1) in which the central silver(I) atom adopts a distorted trigonal planar geometry by coordinating two carbon atoms of the methane moieties of the ligand and one oxygen atom of the NO₃^? group. Interaction of CF₃COOAg with one equiv. of L produced a one-dimensional coordination polymer [Ag₂(μ-L)(CF₃CO₂)₂]_n (2). Each silver(I) in 2 exhibits highly distorted square planar coordination geometry that connects one oxygen atom of L and one neighboring Ag atom with the Ag?Ag interactions. Reaction of HgCl₂ with one equiv. of L resulted in the formation of one-dimensional [{Hg(μ-Cl)Cl}₂(μ-η¹-L)]_n (3) with a C-coordinated dinuclear mercury(II) chloride moiety being linked by L.     

p-Nitrophenyl acetate hydrolysis promoted by Zn(II) and Co(II) complexes with the tripodal ligand of N,N′-bis(2-quinolinylmethyl)amantadine

To mimic the function of metallohydrolase, [M(bqad)Cl₂] (M = Zn(II) (1), Co(II) (2), where bqad = N,N′-bis(2-quinolinylmethyl)amantadine), have been synthesized and characterized by elemental analysis, electronic absorption, IR, and single crystal X-ray diffraction. The structural analysis indicated that metal ions in 1 and 2 were coordinated by three nitrogens from bqad and two chlorides, resulting in a distorted trigonal bipyramidal geometry. Kinetic experiments for hydrolytic cleavage of p-nitrophenyl acetate (pNA) catalyzed by 1 and 2 were performed at pH 7.50–10.00 and 298 K. The second-order rate constants (k_obs) increased exponentially with variation of pH values. The Co(II) complex exhibited potent catalytic activity.     

Synthesis,crystal structures and luminescent properties of phenylmercury(II) complexes with thiohydrazone ligands having weak Hg····π and Hg····Hg interactions

The Reaction of phenylmercury(II) acetate with salicylaldehyde morpholine N-thiohydrazone (H₂smth) and 2-hydroxyacetophenone morpholine N-thiohydrazone (H₂apmth) in dry ethanol under gentle refluxing condition form light yellow complexes [PhHg(Hsmth)] (1) and [PhHg(Hapmth)] (2) involving formation of Hg-S bond from the thiol form of the ligands after deprotonation of the SH proton. The structures of the complexes as determined by X-ray crystallography shows that the complex (1) has a distorted T-shaped geometry while the complex (2) adopts familiar linear coordination geometry. Complex (2) has two independent molecules comprising the asymmetric unit. Both the complexes form two-dimensional supramolecular assemblies due to a combination of weak intermolecular Hg····π and Hg····Hg interactions. The Hg····π and Hg····Hg distances are 3.937 and 4.0216(10) Å, respectively, possibly indicating weak mercuriophilic interactions. The luminescent properties of the complexes in solution and in the solid state at room temperature are also described.     

Zinc(II) complexes with the tetradentate schiff base ligand N,N′-bis(1-pyridin-2-yl-ethylidene)propane-1,3-diamine: Synthesis and crystal structures

Two new zinc(II) complexes [ZnL(N₃)]·BF₄ (1) and [ZnBrL]·BF₄ (2), derived from the tetradentate Schiff base ligand N,N′-bis(1-pyridin-2-yl-ethylidene)propane-1,3-diamine (L), are prepared and characterized by physicochemical methods and single crystal X-ray crystallography. The crystal of (1) is triclinic: space group P-1, a = 8.593(1) Å, b = 8.752(1) Å, c = 13.393(2) Å, α = 97.153(1)°, β = 93.046(1)°, γ = 91.577(1)°, V = 997.4(2) ų, Z = 2. The crystal of (2) is triclinic: space group P-1, a = 8.351(1) Å, b = 8.956(1) Å, c = 13.139(2) Å, α = 92.716(1)°, β = 94.241(2)°, γ = 95.016(1)°, V = 974.8(2) ų, Z = 2. The geometries of the penta-coordinated zinc atoms in both complexes are intermediate between the square pyramid and the trigonal bipyramid having the Addison parameters of 0.39 and 0.47 respectively. The syntheses of the complexes show distinct preference for the anions in the order Br^? > N ₃ ^? > CH₃COO^?.     

A new route to the asymmetric Schiff base ligands. The ligand exchange in [Mo(CN)<Subscript>3</Subscript>O(salhy)]<Superscript>2−</Superscript> ion. Kinetics and mechanism

The kinetics of the ligand exchange in (PPh₄)₂[Mo(CN)₃O(salhy)]. 6H₂O (Hsalhy = salicylaldehyde hydrazone) by a solvent molecule and by 2,2-bipyridine (bpy) have been studied in EtOH. For the ligand exchange by a solvent molecule the pseudo-first order rate constant equals k _obs = 3.2 (±0.2) × 10^–3 s^–1 (t=25 °C), H =67 (± 7) kJ mol^–1, S =–75 (±23) J mol^–1 K^–1, while for the exchange by a bpy molecule k _obs=3.5 (±0.2) × 10^–3 s^–1 (t=25 °C), H =56 (±7) KJ mol^–1, S = –104 (±8) J mol^–1 K^–1. It was found, that all reactions proceed via the same mechanism which involves the chelate ring opening cis to the Mo=O bond. The mechanism of the reaction was proposed and was proved by the synthesis of (PPh₄)₂[Mo(CN)₃O(N-pic)]. 2.5H₂O (N-pic denotes that the nitrogen of picolinic acid is trans to Mo=O) by ligand exchange in EtOH, while in aqueous solution the O-pic analogue is formed exclusively.     

Synthesis,spectroscopic studies and crystal structures of Re<Superscript>I</Superscript>(CO)<Subscript>3</Subscript>(NN)Cl complexes with <Emphasis Type="Italic">N,N</Emphasis>′-bis(substituted benzylidene)ethane-1,2-diamine Schiff base ligands

Four new Re(I) tricarbonyl-diimine complexes were prepared by reaction of Re(CO)₅Cl with N,N′-bis(substituted benzylidene)ethane-1,2-diamine Schiff base ligands. These compounds were characterized by physico-chemical methods, and their crystal structures were established by X-ray diffraction. The coordination geometry at the Re atom is that of a distorted octahedron, with three carbonyl ligands in the facial geometry.     

A series of (NHC)Pd(N˄O)(OAc) complexes: synthesis,characterization and catalytic activities towards desulfinative Sonogashira coupling of arylsulfonyl hydrazides with arylalkynes

A series of well-defined N-heterocyclic carbene palladium (II) complexes with general formula (NHC)Pd(N^˄O)(OAc) were prepared through reaction of Pd (NHC)(OAc)₂(H₂O) with 1-methyl-1H-pyrazole-3-carboxylic acid or 1-methyl-1H-indazole-3-carboxylic acid in the presence of K₂CO₃. These complexes were then used for desulfinative Sonogashira coupling of arylsulfonyl hydrazides with terminal alkynes. With low catalyst loading, all synthesized palladium compounds exhibited moderate to high catalytic activities for the reactions.     

A theoretical study of keto-enol isomerism and internal rotation in the H<Subscript>2</Subscript>Salen molecule,N,N′-ethylene-bis(salicylidenimine) — schiff base

Geometric parameters, vibrational spectra, and the energies of isomerization of seven keto-enol isomeric forms of the H₂Salen molecule (N,N′-ethylene-bis(salicylidenimine)) are calculated using electron density functional theory (DFT/B3LYP) and correlation consistent valence triple-zeta Gaussian basis sets (cc-pvtz). The isomer with two enol groups (EE₁) and C ₂ symmetry configuration is most energetically favorable. Calculations of the keto-enol equilibrium show that at T ≥ 250 K the H₂Salen gas phase is a mixture of four conformers (rotamers of the main isomer EE₁). The contribution of other isomers does not exceed a few percent. The NBO analysis reveals that the system of π-conjugated bonds involves not only the atoms of the benzene moiety, but also the O, C, and N atoms nearest to the benzene ring. The energy stabilization of the isomer EE₁ is shown to be due to the presence of two strong intramolecular N...H hydrogen bonds. Intramolecular N...H and O...H hydrogen bonds are observed in all other isomers. The bathochromic shift of O-H and N-H vibrational frequencies, caused by the effect of hydrogen bonds, is 520–790 cm⁻¹.