The Structure of 2,5-Semiquinones derived from 1,6-Bridged [10] Annulenes

ESR. spectra are reported for the radical anions of the diketones I and II (see below), recently prepared from 1, 6-methano[10]annulene and its 11, 11-difluoro-derivative, respectively [1]. The π-spin populations of I? and II? are shown to be incompatible with the structure A an enedione-norcaradiene. Although the alternative structure B of a [10]annulenequinone is acceptable for both I? and II?, the ESR. data is more satisfactorily rationalized in terms of a structure ‘intermediate’ to A and B. This is particularly true for the radical anion I?, for which the π-spin populations suggest a structural ‘shift’ B → A relative to II?. Structures A and B were postulated [1] for the neutral diketones I and II, respectively.     

Equilibres conformationnels de glucides au niveau de liaisons s̀ sp2-sp3 C?C. II Dérivés d'hydrozones d'aldéhydo-sucres

A series of alkyl-and aryl-hydrazones of different types of aldehydo-sugars with blocked hydroxy groups have been studied, mainly by PMR. spectroscopy. No traces of the azoalkane or ene-hydrazine forms were detected; the hydrazones were found to exist only in the syn form, except for the cases where an intramolecular hydrogen bond between the ‘amino’ hydrogen of the hydazono group and an oxygen o the glycosyl group provides an extra-stabilization to the anti isomer. Most of these syn hydrazones seem to exist as an equilibrium of the ‘classical’ eclipsed rotamers. The influence of solvent polarity both on configurational and conformational equilibria has been examined. The factors which determine the relative stability of the conformers about a sp²-sp³ s? bond, particularly some kind of non-bonded attraction, are discussed.     

Building [2]Catenanes around a Tris(diimine)ruthenium(2+) ([Ru(diimine)3]2+) Complex Core Used as Template

In the course of the last two decades, the use of transition metals as templates for constructing catenanes has almost exclusively been restricted to tetrahedral copper(I). The present work is dealing with an octahedral metal, ruthenium(II), coordinated to three bidentate chelates. Incorporation of two chelates (1,10‐phenanthroline) in a ring allows to prepare a C₂‐symmetric ruthenium complex, the two chelates being disposed cis to one another (see 14 ²⁺ and 16 ²⁺ in Scheme 5 and 6, resp.). The ring is large enough to accomodate a third chelate, thus allowing the metal‐directed threading of a long fragment containing the third chelate (2,2′‐bipyridine derivative; see 23 ²⁺ and 24 ²⁺ in Scheme 8). The last step consists of a ring‐closing metathesis reaction with two terminal olefins. The two ruthenium(II)‐complexed catenanes 25 ²⁺ and 26 ²⁺ were prepared by using this strategy, each containing a 42‐membered ring interlocked to a larger macrocycle (50‐ or 63‐membered ring) incorporating the two 1,10‐phenanthroline chelates. It is expected that these catenanes can be set in motion under light‐irradiation, thus behaving as photochemically driven molecular machines.     

Coordination compounds of transition metal hydrazine derivatives. Part 25. Monohydrazine-S-methylcarbodithioate schiff bases derived from α-dicarbonyl compounds

Summary The monohydrazones derived from the condensation of diacetyl and benzil with hydrazine-S-methylcarbodithioate (Dahydth) and (Benhydth) were prepared and their ligation properties with nickel(II), copper(II), palladium(II), zinc(II) and cadmium(II) were studied. A series of bisligand chelates were isolated and characterized. In the zinc(II), cadmium(II) copper(II) and palladium(II) bisligand chelates, both Dahydth and Benhydth act as mononegative bidentate molecules. The Ni(Dahydth-H)₂ chelate possesses an octahedral structure where Dahydth acts as a mononegative tridentate ligand. The¹H n.m.r. spectra of the two ligands as well as of the diamagnetic metal(II) chelates are discussed. The fragmentation in a mass spectrometer of all these chelates was also studied.     

Bis-adducts formed by nickel(II) and zinc(II) chelates of pyridine-2-(1H)thiones with nitrogen donors

Summary The bis-adducts formed by nickel(II) and zinc(II) chelates of 3-cyano-4-aryl-6-phenyl pyridine-2-(1H)thiones with pyridine and N-methylimidazole have been prepared and characterized by microelemental analyses, i.r., u.v., vis., and ¹Hn.m.r. spectra and magnetic measurements. Owing to Lewis acid-base interactions, the diamagnetic square planar nickel(II) or zinc(II) chelates interact with two molecules of pyridine or N-methylimidazole in the two axial positions forming the corresponding octahedral bis-adducts.     

Reactivity of tert‐butylperoxyl radical with manganese(III), cobalt(II), and nickel(II) salicylidene Schiff base chelates

Salicylidene Schiff base chelates (R,R)‐(–)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediaminomanganese(III) chloride, (R,R)‐(–)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediaminocobalt(II), N,N′‐bis(salicylidene)‐ethylenediaminocobalt(II), N,N′‐bis(salicylidene)ethylenediaminonickel(II), and N,N′‐bis(salicylidene)ethylenediaminoaquacobalt(II), as well as (R,R)‐(–)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)1,2‐cyclohexanediamine, were kinetically examined as antioxidants in the scavenging of tert‐butylperoxyl radical (tert‐butylOO^?). Absolute rate constants and corresponding Arrhenius parameters were determined for reactions of tert‐butylOO^? with these chelates in the temperature range ?52.5 to ?11°C. High reactivity of tert‐butylOO^? with Mn(III) and Co(II) salicylidene Schiff base chelates was established using a kinetic electron paramagnetic resonance method. These salicylidene Schiff base chelates react in a 1:1 stoichiometric fashion with tert‐butylOO^? without free radical formation. Ultraviolet–visible spectrophotometry and differential pulse voltammetry established that the rapid removal rate of tert‐butylOO^? by these chelates is the result of Mn(III) oxidation to Mn(IV) and Co(II) oxidation to Co(III) by tert‐butylOO^?. It is concluded that removal of alkylperoxyl radical by Mn(III) and Co(II) salicylidene Schiff base chelates may partially account for their biological activities. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 431–439, 2007     

Spectrophotometric Studies of Nickel(II) and Copper(II) Chelates of p-(2-Hydroxy-1-Naphthylazo)-Benzenesulphonate

The ionization constant of p-(2-hydroxy-1-naphthylazo)benzene-sulphonate (Orange II) and the formation constants of the metal chelates of this reagent with Ni(II) and Cu(II) have been determined spectrophotometrically in aqueous solution at 25° and at an ionic strength of 0.10M. The ionization constant of orange II was found to be pK_a=10.95. Formation of orange II chelates with Ni(II) and Cu(II) was pH dependent, and the optimum pH range of the Ni(II) Chelate was at pH 9.2-9.4, and Cu(II) chelate at 9.5-9.7, respectively. The mole ratio of orange II to both of metal ions was found to be 2 to 1 stoichiometry. The formation constants (logK) of the Ni(II) and Cu(II) chelates were 12.50 and 16.11, respectively. The molar extinction coefficients and the photometric sensitivities of these chelates were determined.     

CHLOROPHYLL a FLUORESCENCE OF GONYAULAX POLYEDRA GROWN ON A LIGHT-DARK CYCLE AND AFTER TRANSFER TO CONSTANT LIGHT

Abstract— The chlorophyll a fluorescence properties of Gonyaulax polyedra cells before and after transfer from a lightdark cycle (LD) to constant dim light (LL) were investigated. The latter display a faster fluorescence transient from the level ‘I’ (intermediary peak) to ‘D’ (dip) to ‘P’ (peak) than the former (3 s as compared to 10 s), and a different pattern of decline in fluorescence from ‘I’ to ‘D’ and from ‘P’ to the steady state level with no clearly separable second wave of slow fluorescence change, referred to as ‘s' (quasi steady state)→‘M’ (maximum) →‘T’ (terminal steady state). The above differences are constant features of cells in LD and LL, and are not dependent on the time of day. They are interpreted as evidence for a greater ratio of photosystem II/photosystem I activity in cells in LL. After an initial photoadaptive response following transfer from LD to LL, the cell absorbance at room temperature and fluorescence emission spectra at 77 K for cells in LL and LD are comparable. The major emission peak is at 685–688 nm (from an antenna Chl a 680, perhaps Chl a-c complex), but, unlike higher plants and other algae, the emission bands at 696–698 nm (from Chl a_II complex, Chl a 685, close to reaction center II) and 710–720 nm (from Chl a₁, complexes, Chl a 695, close to reaction center I) are very minor and could be observed only in the fluorescence emission difference spectra of LL minus LD cells and in the ratio spectra of DCMU-treated to non-treated cells. Comparison of emission spectra of cells in LL and LD suggested that, in LL, there is a slightly greater net excitation energy transfer from the light-harvesting peridinin-Chl a (Chl a 670) complex, fluorescing at 675 nm, to the other antenna chlorophyll a complex fluorescing at 685–688 nm, and from the Chl a., complex to the reaction center II. Comparison of excitation spectra of fluorescence of LL and LD cells, in the presence of DCMU, confirmed that cells in LL transfer energy more extensively from the peridinin-Chl a complex to other Chl a complexes than do cells in LD.     

Solvolysen von 4-Alkylidenbicyclo[3.2.0]hept-2-en-6-olen. Synthese von 1-Vinylfulvenen und 8,8-Diphenylheptafulven

Solvolysis of 4-Alkydenbicyclo[3.2.0]hept-2-en-6-oles. Synthesis of 1-Vinylfulvenes and 8,8-Diphenylheptafulvene Four 4-alkylidenebicyclo[3.2.0]hept-2-en-6-ones 2–5 , obtained via ketene cycloaddition to fulvenes, were reduced to separated mixtures of the ‘endo’ -alcohols ‘endo’- 6 to ‘endo’- 9 (68–73%) and ‘exo’- 6 to ‘exo’- 9 (3–20%). Treatment of some of these alcohols with (CF₃SO₂)₂O in CH₂Cl₂/pyridine caused a spontaneous solvolysis to yield unsaturated 7-membered rings as pyridinium triflates 10–12 or 1-vinylfulvenes 13 and 14 , a new class of reactive tetraenes: Both ‘endo’- 9 and ‘exo’- 9 , having two methyl groups at C(7), were converted into the vinylfulvene 13 (≈ 80%). The alcohols with two H-atoms at C(7) exhibited a stereochemically controlled reaction selectivity, inasmuch as ‘endo’- 6 to ‘endo’- 8 afforded only the corresponding 7-membered-ring pyridinium salts 10–12 (66–79%), while ‘exo’- 6 produced only the vinylfulvene 14 (77%). A stereoelectronic control argument explains the C(1), C(5)-bond cleavage with ‘endo’- B and ‘endo’– 6 -‘endo’- 8 , as well as the C(1), C(7)-bond cleavage with ‘exo’- B , ‘exo’- 6 , and with both ‘endo’- and ‘exo’- 9 . Thermolysis (120°) of the pyridinium triflates 10 and 11 yielded the 3-isopropenyl-cycloheptatrienes 18 and 19 , respectively (≈90%); similar conditions (145°) applied to the triflate 12 produced the doubly cyclized fluorene derivative 21 (60%). When the iodide 22 derived from the triflate 12 with Nal was heated in refluxing toluene, 8,8-diphenylheptafulvene ( 23 , 86%) was obtained.     

A tetradentate bisoxime and its supramolecular nickel(II) cluster: synthesis,crystal structure,and spectral properties

Salen-type bisoxime 5,5′-dimethoxy-2,2′-[(ethylenedioxy)bis(nitrilomethylidyne)]diphenol (H₂L) and its trinuclear Ni(II) cluster {[(NiL)(n-BuOH)]₂(μ-OAc)₂Ni}?·?n-BuOH have been synthesized and structurally characterized. The structure of H₂L adopts an L-shape conformation where the two salicylaldoxime moieties are well separated. In the trinuclear Ni(II) cluster, two acetates coordinate to three Ni(II)'s through Ni–O–C–O–Ni bridges, four μ-phenoxos from two [NiL(n-BuOH)] units also coordinate to Ni(II), and two n-butanols coordinate to two terminal Ni(II)'s forming a distorted octahedral geometry. The Ni–O–C–O–Ni and μ-phenoxo bridges play important roles in assembling Ni(II) and the ligands. H₂L forms a rectangle-like large cave structure through O–H?···?N, C–H?···?O, and C–H?···?π hydrogen-bond interactions, whereas its trinuclear Ni(II) cluster exhibits a 3-D supramolecular network structure through intermolecular O–H?···?O, C–H?···?O, and C–H?···?π hydrogen-bond interactions.     

An Unexpected Atropisomerically Stable 1,1‐Biphenyl at Ambient Temperature in Solution,Elucidated by Vibrational Circular Dichroism (VCD)

Biphenyls with only two substituents at the ‘peri'‐position normally show rotation about their chiral axis at room temperature. Using vibrational circular dichroism (VCD), we found no evidence for rotation of (P)‐2′‐[(4S)‐4,5‐dihydro‐4‐(1‐methylethyl)oxazol‐2‐yl][1,1′‐biphenyl]‐2‐methanol ((P,S)‐ 1 ) in CDCl₃ about its chiral axis due to stabilization by intramolecular H‐bonding. All rotamers of 1 were calculated at the DFT level, and, from these optimized structures, the VCD spectra were calculated and compared to the measured VCD spectra. The best agreement between calculated and measured spectra is obtained when two rotamers are present in solution. These rotamers differ primarily in their intramolecular H‐bonding interactions, having either OH???N (the form present in the solid state) or OH???O H‐bonds, i.e., a rotation of the heterocycle in 1 takes place in solution.     

Coordination compounds of hydrazine derivatives with transition metals. Part 21. Reaction of 1,5-thiocarbodihydrazones with nickel(II) and copper(II) salts

Summary A series of 1,5-thiocarhodihydrazones (HL) were reacted with nickel(II) acetate to give neutral bisligand nickel(II) chelates, Ni(L)₂. Reaction of nickel(H) chloride, however. results in partial hydrolysis of the dihydrazones to give Ni(RCH=NNHCSNHNH₂)₂Cl₂ chelate complexes. Deprotonation of these chelates with pyridine gave the neutral chelates Ni(RCH=NN=CSNHNH₂)₂. Copper(H) salts are readily reduced by the dihydrazone ligands to copper(I) chelates of the type CuL, Cu(HL)₂CI and Cu₂(HL)₃CI₂.     

Electrofugal Fragmentation of Alkylcobalamin Derivatives Using Cob(I)Alamin and Heptamethyl Cob (I)yrinate as Catalysts

The cob (I)alamin- ( 1(I) ) and the heptamethyl cob(I)ynnate- ( 2(I) ) catalyzed transformation of an epoxide to the corresponding saturated hydrocarbon 3→4→5 is examined (see Schemes 1 and 3–5). Under the reaction conditions, the epoxyalkyl acetate 3 is opened by the catalysts with formation of appropriate (b?-hydroxyalkyl)-corrinoid derivatives ( 13 , 14 , 17 , 18 , see Schemes 12 and 14). Triggered by a transfer of electrons to the Co-corrin-π system, the Co, C-bond of the intermediates is broken, generating the alkenyl acetate 4 (cf. Schemes 12 and 14) following an electrofugal fragmentation (cf. Schemes 2 and 12). The double bond of 4 is also attacked by the catalysts, leading to the corresponding alkylcorrinoids ( 15 , 19 , see Schemes 12 and 14) which in turn are reduced by electrons from metallic zinc, the electron source in the system, inducing a reductive cleavage of the Co, C-bond with production of the saturated monoacetate 5 (see Schemes 2, 5 and 12). In the cascade of steps involved, the transfer of electrons to the intermediate alkylcorrinoids ( 13–15 , 17–19 , see Schemes 12 and 14) is shown to be rate-limiting. Comparing the two catalytic species 1(I) and 2(I) , it is shown that the ribonucleotide loop protects intermediate alkylcobalamins to some extent from an attack by electrons. The protective function of the ribonucleotide side-chain is shown to be present in alkylcobalamins existing in the base-on form (cf. Chap. 4 and see Scheme 14).     

Chiral Acylsilanes in Organic Synthesis. Diastereoselective 1,2-Additions to Racemic Alkoxymethyl-Substituted Acylsilanes

The synthesis of the three alkoxymethyl-substituted acyisilanes 1 – 3 is described (Schemes 1 and 2). Their reactions with NaBH₄ as well as PhLi gave the corresponding alcohols with moderate to good diastereoisomeric induction (up to 78% de; see Table), depending upon the solvent used (Scheme 3). The results indicate that in Et₂O, the reactions with PhLi proceed via 6-membered chelates (see C in Scheme 4) leading to the products with high de's (74–78%). In THF, these chelates are not formed, and as a consequence, the additions take place with reversed and lower stereoselectivities (34–50% de).     

Equilibres conformationnels de glucides au niveau de liaisons σ sp2-sp3 C-C. III Dérivés d'oximes d'aldéhydo-sucres utilisation de tris-dipivaloylméthanato-europium

A series of sugar oximes and O-methyloximes of the general formula RCH?NOR′ (R′ ? H, CH₃) have been studied by PMR. spectroscopy. These compounds exist in solution as a mixture of the syn and anti isomers. The conformational equilibrium of the syn isomers seems to consist exclusively of the eclipsed rotamers, whereas for the anti isomers there appears to be a significant contribution from bisecting rotamers. Using tris-dipivaloylmethanato-europium it is found that the α proton of the anti oximes is much more deshielded than the corresponding proton of the syn isomers, which means that the downfield shift of a particular proton does not depend exclusively on its distance from the oxygen of the oxyimino group.     

Preparations,IR spectra and crystal structures of cyano-bridged bimetallic complexes of zinc(II) and cadmium(II) with tetracyanopalladate(II)

The novel heteronuclear compounds [Zn(hydet-en)₂Pd(CN)₄] (1) and [Cd(hydet-en)₂Pd(CN)₄] (2) {hydet-en: N-(2-hydroxyethyl-ethylenediamine)} have been synthesized and characterized by elemental analyses and IR spectra. The crystal structures of 1 and 2 have been determined by X-ray diffraction. Structural analysis shows that both compounds have shown a polymeric chain, in which the Zn(II)/Pd(II) and Cd(II)/Pd(II) centres are linked by two CN groups. Both zinc and cadmium atoms are six coordinate with two trans cyanide–nitrogen and four hydet-en N atoms in a distorted octahedron arrangement; the palladium atoms in 1 and 2 are four coordinate with four cyanide-C atoms in a square planar arrangement. The chains in both compounds are connected through weak interchain hydrogen bonds, N–H?···?O, N–H?···?N and O–H?···?N, thereby forming a three-dimensional network.     

ABSORPTION,LUMINESCENCE, SOLVENT-INDUCED CIRCULAR DICHROISM AND1H NMR STUDY OF BILIRUBIN DIMETHYL ESTER: OBSERVATION OF DIFFERENT FORMS IN SOLUTION*

Bilirubin dimethyl ester (I) has been studied by absorption, fluorescence and fluorescence excitation, solvent-induced circular dichroism, and ¹H NMR techniques. The existence of two forms of the solute involving either or both syn-anti dipyrromethenone and lactam-lactim equilibria was established, and the occurrence of even more forms remains possible. The relative population is strongly influenced by the nature of the solvent and by temperature. Thus, the population of one species predominates in ethanol. What is presumed to be the same species increases on cooling in all solvents, while the population of another species is strongly preferred in dichloromethane. In other solvents appreciable populations of both forms persist over the temperature range 77–300 K.     

Spectrophotometric Studies of Cobalt(II) and Copper(II) Chelates of 2-Picolylamine

Cobalt (II) and copper (II) chelates of 2-picolylamine have been studied spectrophotometrically in aqueous solution. Formation of 2-picolylamine chelates was pH dependent, and the optimum pH range of the cobalt (II) chelate was at pH 8.8-9.6, and copper(II) chelate at 4.7-6.8, respectively. The mole ratio of 2-picolylamine to both of metal(II) ions was found to be 2 to 1 stoichiometry. The spectrophotometric sensitivities are 0.23γ of Co/Cm² and 8.9γ of Cu/Cm³, at 373 mμ, pH 9.0 for Co(II) chelate and 588 mμ, pH 6.0 for Cu (II) chelate. The stability constants (logK) of the chelates CoL₂²⁺ and CuL₂²⁺ have been evaluated at a constant ionic strength of 0.10 at 20, 25, 30, 35 and 40°C. Enthalpy and entropy changes characterizing the formation of the chelates have been calculated at 25°C The results are collected as follows:      

Z and E rotamers of N‐formyl‐1‐bromo‐4‐hydroxy‐3‐methoxymorphinan‐6‐one and their interconversion as studied by 1H/13C NMR spectroscopy and quantum chemical calculations

N‐Formyl‐1‐bromo‐4‐hydroxy‐3‐methoxymorphinan‐6‐one (compound 2 ), an important intermediate in the NIH Opiate Total Synthesis, presumably exists as a mixture of two rotamers (Z and E) in both CHCl₃ and DMSO at room temperature due to the hindered rotation of its N‐C18 bond in the amide moiety. By comparing the experimental ¹H and ¹³C chemical shifts of a single rotamer and the mixture of compound 2 in CDCl₃ with the calculated chemical shifts of the geometry optimized Z and E rotamers utilizing density functional theory, the crystalline rotamer of compound 2 was characterized as having the E configuration. The energy barrier between the two rotamers was also determined with the temperature dependence of ¹H and ¹³C NMR coalescence experiments, and then compared with that from the reaction path for the interconversion of the two rotamers calculated at the level of B3LYP/6‐31G*. Detailed geometry of the ground state and the transition states of both rotamers are given and discussed. Copyright © 2012 This article is a US Government work and is in the public domain in the USA.     

Metallionen und H2O2. IV. Über Struktur und Aktivität der den H2O2-Zerfall katalysierenden Cu2+-Komplexe. II. Einfluss der Zahl der freien Koordinationsstellen

The Cu²⁺ chelates of the bidentate ligands 2,2′-bipyridine (I; [2]), N, N′-diglycyl-1,5-diaminopentane (VI), ethylenediamine (II; [2]), glycine (V) and pyrophosphate (III; [2]) are found–parallel to the spectrochemical series–to be more active in catalysis of H₂O₂ decomposition than the chelates of the terdentate ligands–antiparallel to the spectrochemical series–iminodiacetic acid (IX), glycylglycine (VIII), 2, 2′-diaminodiethylamine (VII) and 2, 2′, 2″-terpyridine (IV; [2]), the activity decreasing in the given series. If all four coordination positions of Cu²⁺ are engaged (e.g. complex with N, N′-di-(2-aminoethyl)-ethylenediamine (X)) the complex is inactive. The catalytic activity of the Cu²⁺-chelates is parallelled by the tendency to form ternary peroxo complexes.