Yellow Adduct Research Articles

Characterization of a paramagnetic mononuclear nonheme iron-superoxo complex.

O2 bubbling into a THF solution of FeII(BDPP) (1) at −80 °C generates a reversible bright yellow adduct 2. Characterization by resonance Raman and Mössbauer spectroscopy provides complementary insights into the nature of 2. The former shows a resonance-enhanced vibration at 1125 cm–1, which can be assigned to the ν(O–O) of a bound superoxide, while the latter reveals the presence of a high-spin iron(III) center that is exchange-coupled to the superoxo ligand, like the FeIII–O2– pair found for the O2 adduct of 4-nitrocatechol-bound homoprotocatechuate 2,3-dioxygenase. Lastly, 2 oxidizes dihydroanthracene to anthracene, supporting the notion that FeIII–O2– species can carry out H atom abstraction from a C–H bond to initiate the 4-electron oxidation of substrates proposed for some nonheme iron enzymes.

Highly facile homogeneous epoxidation of olefins using oxo-diperoxo tungstate(vi) complex as catalyst, bicarbonate as co-catalyst and hydrogen peroxide as a terminal oxidant

Addition of a dilute acetic acid solution of 8-quinolinol to an H2O2 solution of freshly precipitated H2WO4·2H2O furnishes a yellow adduct [WO(O2)2·2QOH] 1 which, on crystallization from a suitable solvent, affords orange-yellow complex [WO(O2)(QO)2] 2. When 2 reacts stoichiometrically with olefinic compounds in a 1∶1 molar ratio, the respective olefins are epoxidized and 2 is converted to the orange-red [WO2(QO)2] 3. When 1 is treated with an excess of H2O2 (greater than 6 equiv.) and PPh4Cl, an anionic light yellow complex PPh4[WO(O2)2(QO)] 4 is obtained. 4 reacts with cyclopentene (a representative olefin) in a 1∶1 molar ratio producing cyclopentene oxide and itself is converted to PPh4[WO2(O2)(QO)] 5. If the above reaction is conducted at a 1∶2 molar ratio (instead of 1∶1) then 2 moles of the corresponding epoxide is formed and 4 is converted to PPh4[WO3(QO)] 6. All these peroxo complexes have remarkable catalytic efficiencies in the epoxidation of olefinic compounds when used in tandem with NaHCO3 as co-catalyst and H2O2 as oxidant in a CH3CN medium at room temperature, the method being green and economical. The catalyst 4under the above experimental conditions shows so far unmatched efficiency in epoxidizing a wide variety of olefinic substrates.

Photochromic Behavior and Diastereomeric Isomerism in [(η6-spirobenzopyran)RuCp*]PF6

Complexation of photochromic spirobenzopyran 1 (SP-X) with the labile cationic ruthenium complex [Cp*Ru(NCMe)3]PF6 (2) furnishes two isomers of the η6-arene adducts, [Cp*Ru(η6-SP-X)]PF6 (3 and 4), i.e., one of the two diastereomeric adducts of the indoline part in the closed form of 1 (3) and the adduct of the dihydrobenzopyran part in the open trans-merocyanine form of 1 (4). UV irradiation of the pale yellow adduct 3 does not cause an apparent color change, but 1H NMR monitoring reveals formation of the diastereomer 3‘ with the inverted configuration of the chiral spiro carbon atom, which gradually reverts to 3 when left at ambient temperature in the dark over the course of a few days. The two diastereomers 3/3‘ are interconverted with each other through the open, merocyanine form III, which should result from photochemical C−O bond heterolysis of 3/3‘. In the case of the SP-H complex 3b, photochromic behavior (3b ↔ III‘b (trans isomer of IIIb)) is noted but the amount of the colored species III‘b formed is limited. On the other hand, irradiation of the deep red isomer 4 with visible light brings about trans to cis isomerization of the olefinic part to result in complete conversion to an equilibrated mixture of the two diastereomeric closed species 5 and 5‘, which are interconverted with each other at ambient temperature via the transient cis-open intermediate II. UV irradiation of the equilibrated mixture 5/5‘ reverses the ring-opening process to give a photoequilibrated mixture containing 4 in addition to 5/5‘. Thus, 3 and 4 undergo interconversion of the diastereomers via photochemical C−O bond heterolysis and photochromic behavior is noted for 4.

Synthesis and structures of diphosphinoamide complexes of nickel, palladium and platinum

Lithium bis(diphenylphosphino)amide, (THF) 3LiN(PPh 2) 2 reacts with Ni(COD) 2 or PtMe 2(COD) to give the corresponding bimetallic complexes (THF) 3LiN(PPh 2) 2Ni(COD) and (THF) 3LiN(PPh 2) 2PtMe 2. Reaction of (THF) 3LiN(PPh 2) 2Ni(COD) with Me 3SnCl gave the Ni–Sn derivative, also accessible from Me 3SnN(PPh 2) 2. The silyl derivatives Me 3SiN(PPh 2) 2M [M = Ni(COD), PtMe 2] were obtained similarly as red and colourless crystals, respectively. By contrast, the reaction with PdCl 2(COD) afforded an insoluble yellow adduct which, on attempted recrystallisation afforded a small amount of a Pd(I) product, [PdCl{HN(PPh 2) 2}] 2. The crystal structures of the Ni and Pt complexes are based on MP 2N four-membered rings. The geometric parameters proved rather insensitive to changes in the N-main group element bond. In all cases the amido-nitrogen atom deviated slightly from trigonal-planar geometry, most probably as the consequence of packing forces.

Spectrophotometric determination of fenoterol hydrobromide in pure form and dosage forms

A sensitive and rapid spectrophotometric procedure has been investigated for the determination of fenoterol either per se or in pharmaceutical preparations. The proposed procedure is based on the reaction between the drug and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) at pH 7.2, using borate buffer, to produce a yellow adduct. The latter has maximum absorbance at 400 nm and obeys Beer's law within the concentration range 5–30 μg/ml. Regression analysis of the calibration data showed a good correlation coefficient ( r=0.9996) with minimum detection limit of 0.24 μg/ml (6.2×10 −8 M). The proposed procedure has been successfully applied to the determination of this drug in its tablets and in syrup, the mean percent recoveries were 97.45±0.59 and 98.7±0.64%, respectively. The results obtained are in good agreement with those given using a reference method. The pharmaceutical additives other than active ingredient did not interfere. A proposal of the reaction pathway has been postulated.

1,2-Dihydro[1,3,2]diazaborolo[1,5-a]pyridines: a novel class of heterocycles

Reaction of a pyridine carbaldimine 2-tBuNCHC5H4N 1a with a molar equivalent of boron tribromide afforded a bicyclic 1,3,2-diazaborolium bromide 2a as an orange solid, whereas 1a and the corresponding 2-(2,6-Me2C6H3)N CHC5H4N 1b with two equivalents of boron trifluoride gave non-ionic yellow adducts 3a and 3b. The reduction of compounds 2a, 3a and 3b with an excess of sodium amalgam in a hexane slurry led to the formation of 1-X-2-R-1,2-dihydro[1,3,2]diazaborolo[1,5-a]pyridines 4 (X = Br; R = tBu), 5a (F; tBu) and 5b (F; 2,6-Me2C6H3) as yellow oils (4a, 5a) or a yellow wax (5b), respectively. Treatment of 4 with an excess of chlorotrimethylsilane caused a Br/Cl exchange to afford chloro derivative 6. The addition of a methyl group to the boron atom was effected by reaction of heterocycle 4 with methyllithium. The BCN derivative 8 resulted from treatment of 4 with silver cyanide. Reduction of 4 with lithium aluminium hydride gave the 1-hydro-derivative 9, whereas the BStBu compound was obtained from the reaction of 4 with KStBu. Compound 8 was subjected to an X-ray diffraction analysis.

Reactivity of X3P Compounds with Elemental Sulfur, Carbon Disulfide or Both, to Yield X3PS, X3P.CS2 or X3P.Sn.CS2 Adducts

Kinetic constants k2 have been obtained for the reaction of sulfur with 25 PIII compounds in toluene or hexane. In the series PhnMe3-nP (n = 1−3) or PhnBu3-nP (n = 0−3), log k2 decreases linearly with ∑χi(χi=Tolman's electronic parameter of each ligand on P), taken as a gauge for the donor strength of P. Dramatic deviations from additivity are observed for the series PhnP(OEt)3-n, PhnP(OPh)3-n and BunP(OEt)3-n(n = 0–3); the deviation is smaller for PhnPCl3-n and even smaller for PhnP(NEt2)3-n. The results are discussed in terms of P-coordination (PIV vs. PV), stability and geometry of the intermediate X3P.S8 or of the transition state leading to this adduct, emphasis being laid on the donor/acceptor character of the P site. A similar dependence on X governs the reactivity of X3P with S8, CS2 or both, to give X3PS, X3P.CS2 (binary red adduct) or X3P.Sn.CS2 (ternary yellow adduct) respectively; an explanation for this parallelism is proposed.

Further studies and observations on 2‐thiobarbituric acid assay (fat autoxidtion) and 2‐thiobarbituric acid‐aldehyde reactions

AbstractStudies both on the 2‐thiobarbituric acid assay (fat autoxidation, fat rancidity) and 2‐thiobarbituric acid‐aldehyde reactions were carried out. Physico‐chemical properties in solution of the reagents (2‐thiobarbituric acid, malonaldehyde) and the red adduct, especially, were evaluated. The 2‐thiobarbituric acid structure did not change if heated in diluted acid media (until 1% v/v concentration for strong acids) or in 50% v/v concentration for weak acids, as acetic acid. For high acid concentrations, especially with oxyacids (phosphoric acid, trichloroacetic acid), an oxidant hydrolytical effect can be observed. Diluted solutions of malonaldehyde, in a diluted weak acid medium, remained stable for more than ten days. For the first time the stoichiometries of the red and yellow adducts in solution were determined. Both the absorption maxima and molar absorptivity of the red adduct in acid medium were determined. The neutral and alkaline media were less favourable for the assay sensitivity and stability. The more suitable organic solvents for using in the optimized 2‐thiobarbituric acid assay in aqueous medium were cyclohexane, chloroform and the ethers, because the red adduct was not very soluble (less than 0.1 g/1) in the organic solvents (fat extractors).

Intramolecular [4 + 4] photocycloaddition reactions of the photochromic compounds, 3,4-bis(9-anthrylmethylene)tetrahydrofuran-2,5-dione and its 5-dicyanomethylene derivative

The red and the purple photochromic title compounds undergo intramolecular [4 + 4] photocycloaddition reactions on irradiation with white light to form pale yellow and colourless adducts, respectively, which undergo the reverse reactions thermally or on exposure to ultraviolet light.

X-ray structures of adducts of 1,2,5-triphenylphosphole with dimethyl acetylenedicarboxylate: a confirmation, a revision, and a new structure

Dimethyl acetylenedicarboxylate was reacted with 1,2,5-triphenylphosphole under mild conditions, and four products isolated. Regardless of conditions used, every preparation gave low yields of dimethyl 3,6-diphenylphthalate coincident with loss of the phosphorus bridge. NMR data and X-ray crystal structures are provided for a yellow, and a red, 2:1 adduct. The yellow adduct, tetramethyl 1,6,7-triphenyl-6-phospha(V)-tricyclo[7.3.1.01,9]nona-3,5,7-triene-2,3,4,5-tetracarboxylate 6, crystallized in the triclinic space group [Formula: see text] (No. 2) with two molecules in the unit cell. Refinement (a = 11.259(1) Å, b = 12.947(3) Å, c = 13.784(3) Å, α = 112.25(2)°, β = 103.44(1)°, and γ = 101.80(1)°) converged at R = 0.0453 (Rw = 0.0453) for 537 parameters using 2880 reflections with I > 2σ(I). The red adduct, trimethyl 1,2,5-triphenylphosphoranylidene-4-methoxycyclopent-2-ene-5-one-2,3,4-tricarboxylate, an exocyclic phosphorane 8, crystallized in the monoclinic space group P21/c (No. 14) with four molecules in the unit cell. Refinement of this structure (a = 13.233(5) Å, b = 15.712(5) Å, c = 17.191(7) Å, α = 90°, β = 110.35(4)°, and γ = 90°) converged at R = 0.0916 (Rw = 0.0937) for 400 parameters using 2052 reflections with I > 2.5σ(I). Small amounts of a white or buff amorphous material, which could represent a polymeric product from the lost phosphorus bridge, were also obtained. Thermal rearrangement of the yellow adduct gave a colourless 6,5,3 tricyclic isomer 11, possibly via the isomeric cyclopropyl derivative 15 or the nine-membered phosphonin 7. The structure of 11 was confirmed by mild oxidation of the colourless rearrangement product to its P-oxide. This product, tetramethyl 2,3,6-triphenyl-2-phosphatricyclo[6.1.01,8.05,9]-2-oxonona-3,6-diene-1,7,8,9-tetracarboxylate 12, was also colourless. It crystallized in the orthorhombic space group Pbc21 (No. 29) with four pairs of molecules in the unit cell. Refinement of this structure (a = 8.918(1) Å, b = 22.605(4) Å, and c = 30.169(6) Å) converged at R = 0.0747 (Rw = 0.0757) for 321 parameters using 3255 reflections with I > 3σ(I). Unequivocal structures for these adducts and derivatives finally confirms, and establishes further understanding of, the complex reactions of the triphenylphosphole with dimethyl acetylenedicarboxylate.

Interactions of sulfanilamide and 2-thiobarbituric acid with malonaldehyde: structure of adducts and implications in determination of oxidative state of nitrite-cured meats

Reaction of malonaldehyde (MA) with 2-thiobarbituric acid (TBA) in model systems resulted in the formation of the typical pink adduct (TMT) with absorption minima at 278, 372, and 532 nm. Reactions of MA with sulfanilamide (SA) produced a bright yellow adduct (SMS) with absorption minima at 256, 332, and 396 nm. Addition of TBA to the MA-SA system resulted in the disappearance of the characteristic absorption bands of SMS and the appearance of the characteristic absorption bands of TBA-MA as well as a new band at 472 nm

Congregation of gangliosides at the junction between two model membranes

The diversity and distribution of gangliosides in vertebrate tissue suggests an important role in cellular recognition. Two types of experiments are reported to test the hypothesis that gangliosides can congregate to form an adhesive junction between two membranes. First, to monitor ganglioside distribution and mobility in different regions of two large spherical bilayer membranes, fluorescent derivatives of natural gangliosides were synthesized. Second, the cation carrier nonactin was used as a conductance probe to measure the membrane surface potential, which would be altered if there were a redistribution of the charged gangliosides. These studies were conducted in large spherical artificial membranes made from egg phosphatidylcholine or oleoylpalmitoylphosphatidylcholine with 0-12 mol % bovine brain gangliosides dissolved in n-decane. The fluorescent gangliosides utilized were lucifer yellow adducts to the sialic acids (LY-gangliosides) or a cis-paranaric acid substitution of the N-acyl moiety in the ceramide portion of gangliosides GM1 and GD1a (paranaryl-GM1 and paranaryl-GD1a). The polarized fluorescence from the adhesive junction between two membranes containing LY-gangliosides or either paranarylganglioside was compared to that in nonadhesive regions. For LY-gangliosides, total fluorescence in the junction decreased with time, possibly due to electrostatic repulsion of this highly charged derivative. For paranarylgangliosides, fluorescence in the junction increased 7-fold with time, suggesting congregation of this ganglioside. In both cases, a measure of rotational mobility, fluorescence anisotropy, increased dramatically, about 2-fold, as expected for restricted mobility of adhesive compounds. Independent evidence for congregation of charge-bearing gangliosides was found with the conductance probe nonactin.(ABSTRACT TRUNCATED AT 250 WORDS)

Übergangsmetallkomplexe mit Schwefelliganden, LXXII / Transition Metal Complexes with Sulfur Ligands, LXXII

Racemic [Ru(ClH)(PPh3)′S4'] · CH2Cl2 (′S4'2-= 1,2-bis(2-mercaptophenylthio)ethane(2—)) reacts with monodentate sulfur ligands L to yield diastereospecifically yellow adducts [Ru(L)(PPh3)′S4']. Asymmetric achiral thioethers (L = SPhMe, CH3SSCH3) give only one of two potentially possible pairs of enantiomers, chiral thioethers and thiols (L = N-Acetyl-(L)-Methionin, N-Acetyl-(L)Methionin-methylester, S-Methyl-(L)Cystein, N-Acetyl-(L)Cystein) only two of four potentially possible diastereomers in the ratio 1:1. These results prove that the diastereospecifity is related to the coordinated thioether or thiol sulfur atom: It becomes stereogenic in the course of coordination and its configuration is determined by the chirality of the [Ru(PPh3)′S4'] fragment. Additional stereogenic centres in the substituents of chiral thioethers or thiols do not enhance the degree of diastereoselectivity.

Cross-coupling reactions of d2 tantalum alkyne complexes: selective 1,3-diene syntheses and their relevance to alkyne cyclization chemistry

Ta(DIPP){sub 3}Cl{sub 2}(OEt{sub 2}) (DIPP = 2,6-diisopropylphenoxide) can be reduced by two electrons in the presence of the bulky alkynes PhC{triple bond}CPh and Me{sub 3}SiC{triple bond}CMe to provide the pale yellow adducts (DIPP){sub 3}Ta(PhC{triple bond}CPh) (1) and (DIPP){sub 3}Ta(Me{sub 3}SiC{triple bond}CMe) (2). The reduction of Ta(DIPP){sub 3}Cl{sub 2}(OEt{sub 2}) in the presence of smaller internal alkynes (viz. EtC{triple bond}CEt) or the terminal alkynes Me{sub 3}SiC{triple bond}CH or Me{sub 3}CC{triple bond}CH affords metallacyclopentadienes directly. The molecular structure of the PhC{triple bond}CPh adduct 1 is approximately tetrahedral (L-Ta-L angles average 109.4{degree}) and features very short Ta-C{sub alkyne} distances (2.070 (3) and 2.076 (3) {angstrom}, respectively) and an elongated C{triple bond}C' bond (1.346 (5) {angstrom}), which indicate a strongly bound and substantially reduced alkyne ligand. The molecular structure of metallacycle 3 reveals a trigonal bipyramidal geometry (L{sub ax}-Ta-L{sub ax} = 164.9 (3){degree}) with the metallacyclic {alpha} carbons occupying one axial and one equatorial site. The alkyne complex (DIPP){sub 3}Ta(PhC{triple bond}CPh) (1) reacts with MeC{triple bond}CMe, EtC{triple bond}CEt, Me{sub 3}CC{triple bond}CH, Me{sub 3}SiC{triple bond}CH, or PhC{triple bond}CH to afford high yields of the metallacyclization products. The alkyne adduct (DIPP){sub 3}Ta(Me{sub 3}SiC{triple bond}CMe) (2) also engages in metallacyclization chemistry. All of the metallacyclopentadiene complexes canmore » be hydrolyzed with H{sub 2}O/acetone solutions to afford the corresponding 1,3-dienes in essentially quantitative yields.« less

Trans-bis(diphenylphosphine)cyclopropane; a ligand selective for binuclear complexation with ca. 4.5 Å intermetallic separation

trans-1,2-Bis(diphenylphosphinoyl)ethylene was treated with (CH 3) 2S(CH 2) in dimethyl sulphoxide and the product reduced with HSiCl 3 to give trans-bis(diphenylphosphino)cyclopropane in 56% overall yield. The new ligand was found to have a strong affinity for AgBF 4 forming a 2/2 complex under conditions where related ligands gave a mixture of 2/2 and 3/2 adducts. This complex could be employed as precursor to a cationic binuclear rhodium carbonyl complex P 2RH 2 +(CO) 3Cl. When synthesis of the coresponding iridium complex was attempted, a soluble yellow adduct of P 2Ir 2(CO) 2Cl 2 and AgBF 4 was obtained, assumed to contain an IrAgIr bond.

Addition of benzyne to naphtho[2,3- c][1,2,5]selenadiazole

A yellow adduct obtained from benzyne and naphtho[2,3-c][1,2,5]selenadiazole is identified as 3-(10-cyano -9-anthryl)-1,2-benzisoselenazole (7). Sequential addition of dimethyl acetylenedicarboxylate and of benzyne to the same fused 1,2,5-selenadiazole affords 3-(4-cyano-2,3-bismethoxycarbonyl-1-naphthyl)-1,2-benzisoselenazole (12).

The reactions of 3‐Butyl‐1,2‐diphenylphosphindole with dimethyl acetylenedicarboxylate

AbstractUnlike 1,2,5‐triphenylphosphole, 3‐butyl‐1,2‐diphenylphosphindole reacts smoothly with two molecules of dimethyl acetylenedicarboxylate to give the phosphindole oxide, a yellow adduct and a colourless adduct. The case of the reaction is taken to indicate less lone pair interaction with the π‐system in phosphindoles than in phospholes. The yellow adduct is shown to be a phosphindolium cyclopentadienylide, i.e. an adduct of the phosphindole and two molecules of the ester less one oxygen atom. The colourless adduct is shown to be a 1:2:1 adduct of the phosphindole, the ester and water and has a benzodihydrophosphonin structure. Mechanisms for the formation of both adducts are proposed. Adducts of this general type were previously unknown in organophosphorus chemistry.

Electrochemical studies of phenothiazine-iodine charge-transfer complexes

The conductivity of the freshly prepared yellow adduct of phenothiazine and iodine in acetonitrile is due in about equal parts to 2:3 and 1:2 complexes at 20°C. In CH 3CN the complexes are completely dissociated. The equivalent conductivity remains constant, independent of concentration, at 130 mho. cm 2/eq which is of the same order as that of strong electrolytes. The mean mobility of the carriers is 6·2 × 10 −4 cm 2/V.s. Transport numbers were obtained from electrolysis in a Hittorf-type cell as t + = 0·17 and t ± = 0·83, yielding for the mobilities μ − = 1·0 × 10 −3 and μ + = 2·1 × 10 −4 cm 2/V.s. The anions, identified as I 3 −, are thus the majority carriers. It is estimated that the mean radius of the cations is about 2 to 4 times that of a hypothetical benzene ion in the same solvent. Further electrolysis experiments show that the complex formation-dissociation equilibria are reversible. Ageing and/or illumination, or addition of water, causes the colour of the adduct to change first to green, then to blue and eventually to violet. A new absorption initially at 650 nm and considered as a charge-transfer band shifts upon ageing to 625 nm for the green and to 550 nm for the violet adduct. The conductivity of the complex dissolved in acetonitrile rises with temperature at a rate considerably less than that of the pure solvent, the apparent activation energies being 0·003 and 0·06 eV respectively; this is considered as indicating the probability of recombination to rise with increasing temperature. The ground state of the complex in acetonitrile solution is shown to be predominantly ionic and its electronic structure to resemble that of the excited state of the isolated complex molecule.

Reactions of phosphines with acetylenes. Part X. Structure revision of a so-called spirobiphosphole. The rearrangement of a tricycloallylidenephosphorane to a phosph(III)onin

1,2,5-Triphenylphosphole and dimethyl acetylenedicarboxylate (2 equiv.) give a stable yellow adduct, which has been shown to be the tricyclo-allylidenephosphorane (12) rather than a stable spirobiphosphole, as previously suggested. The phosphorane rearranges in boiling chloroform to give a cis,cis,trans,cis-phosph(III)onin (17d). The stereochemistry, n.m.r. (1H and 31P), u.v., and i.r. spectra are discussed.

Reactions of phosphines with acetylenes. Part VII. Structure revision of a rearranged 1:2 adduct of triphenylphosphine and dimethyl acetylenedicarboxylate. A stable 2H-phosph(V)ole

Triphenylphosphine and dimethyl acetylenedicarboxylate (2 equiv.) react to form a yellow adduct, which has been shown to be the stable 2H-phosph(V)ole (10a) rather than an open-chain phosphine as previously postulated. Tri-p-tolylphosphine gives a similar yellow adduct (10b). The temperature-dependent 1H n.m.r. spectra of the adducts in deuteriochloroform solution and in trifluoroacetic acid solution display features characteristic of phosphoranes stabilised by alkoxycarbonyl groups. Treatment of the adduct with zinc and acetic acid gave the open chain phosphine oxide (12). The infrared spectra of allylidenephosphoranes stabilised by methoxycarbonyl groups are discussed.