bluuebunny/crossref_metadata_2025 huggingface dataset:
Stypandrol, a Toxic Binaphthalenetetrol Isolated from Stypandra imbricata
Authors: Colegate SM , Dorling PR , Huxtable CR , Skelton BW , White AH
Published: September 2010

The compound responsible for the toxicity of the plant Stypandra imbricata has been isolated and shown to be 7,7′-diacetyl-6,6′- dimethyl-2,2′-binaphthalene-1,1′,8,8′-tetrol (5) by spectroscopic and single-crystal X-ray diffraction methods.
Complexes of Carbohydrates with Metal Cations. XIV. Separation of Sugars and Alditols by Means of Their Lanthanum Complexes
Authors: Angyal SJ , Mills JA
Published: September 2010

The mobilities of numerous polyols, sugars and methyl glycosides on ion-exchange resin thin-layer plates in the calcium and lanthanum form have been measured. Under these conditions, alditols which have a threo-threo sequence of hydroxy groups complex more strongly with lanthanum than with calcium, whereas methyl glycosides complex less strongly.
The Chemistry of Eremophila spp. XXII. New Eremane Diterpenes from E. fraseri
Authors: Carroll PJ , Engelhardt LM , Ghisalberti L , Jefferies PR , Middleton EJ , Mori TA , White AH
Published: September 2010

The resin components of different collections of the highly variable Eremophila fraseri F. Muell. Have been examined. Five new eremane diterpene acids have been characterized and evidence for their structures is presented. The structure of a new diterpene, also isolated from E. fraseri, has been determined by X-ray crystallographic methods. The carbon skeleton of this new diterpene incorporates a tricyclo[6.2.1.01,5]undecane ring system.
The Prototype centro-Cl-tetrahedro-Zn4-icosahedro-(µ-SPh)12-tetrahedro-(ZnSPh)4 Molecular Structure, and Topological Analysis of Surface Ligand Packing for an Ensemble of High Symmetry M8(µ-SR)12 Aggregates and Derivatives
Authors: Dance IG
Published: September 2010

The aggregate [ClZn8( SPh )16]- (1) has been characterized by diffraction analysis of crystals obtained as the minor product from a mixture of Zn(NO3)2, PhSH , Et3N and Me4NCl in methanol. The new and prototypical structure of (1) contains a bitetrahedron (tetracapped tetrahedron) of zinc atoms, centred by the monatomic ligand and bridged on the twelve edges by thiolate ligands , and with four terminal thiolate ligands. All metal atoms are tetrahedrally coordinated. In terms of expanding concentric regular polyhedra (1) is centro-Cl-tetrahedro-Zn4-icosahedro -(μ- SPh )12-tetrahedro-Zn4-tetrahedro-( SPh )4, introducing the structural principle of aggregation in which metal atoms are inside and outside a regular polyhedron of bridging ligands. The cage framework and the substituents of the bridging ligands virtually adhere to the symmetry of the rare point group T: the packing of obliquely inclined ligand substituents over the surface of the aggregate is responsible for this unusually high symmetry configuration. Alternative aggregate stereochemistries bitetrahedro-M8-cuboctahedro-(μ-SR)12, hexahedro-M8- icosahedro (μ-SR)12, and hexahedro-M8-cuboctahedro-(μ-SR)12, structurally plausible and accessible to (1) without bond breaking or angular strain, are analysed topologically. Again high symmetry is required in the array of substituents from bridging ligands . It is shown that in these aggregates based on a (μ-SR)12M8 framework, the polyhedron formed by the twelve a-carbon atoms of substituents and the S12 polyhedron manifest an icosahedron/cuboctahedron complementarity. Crystal data: orthorhombic P bcn, a 23.493(3), b 29.726(4), c 17.835(2), Z = 8×[Cl0.5Zn4(SC6H5)8- + uncertain cation], 2715 observed data, Cu Kα, R = 0.12. Identification of the central ion of (1) as Cl - rather than the possible alternative s2- is not definite.
Heterocyclic Amplifiers of Phleomycin. VIII. Mono- Bis-(5'-substituted 1',3',4'-thiadiazol-2'-yl)pyridines and Mono(5'-substituted 1',3',4'-thiadiazol-2'-ylmethyl)pyridines
Authors: Barlin GB
Published: September 2010

A series of mono- and bis -(5′-substituted 1′,3′,4′-thiadiazol-2′- yl )pyridines with strongly basic side chains, e.g., 3,5-bis[5′(2′-N,N- dimethylaminoethylthio )-1′,3′,4′-thiadiazol-2′-yl]pyridine (1), and (5?-substituted 1′,3′,4′-thiadiazol-2′-ylmethyl)pyridines have been prepared for evaluation as amplifiers of phleomycin. Five of the six bis (5′-substituted 1′,3′,4′-thiadiazol-2′-yl)pyridines were themselves antibacterial under the test conditions, but compound (1) and the mono(5′-substituted 1′,3′,4′-thiadiazol-2′-yl)-pyridines and -methylpyridines displayed moderate two-to-three-star activity.
Ab Initio Studies on Amides: Pyrrolidin-2-one (γ-Butyrolactam)
Authors: Riggs NV
Published: September 2010

By optimization with the 3-21G basis set, pyrrolidin-2-one is found clearly to prefer an envelope conformation with the flap bent 27.4° out of the NC(=O)C reference plane. The ring may be bent or twisted through a few degrees at low energy-cost, and undergoes rapid inversion through a planar-ring structure lying only 3.3 kJ mol-1 above the preferred equilibrium structure.
Synthesis of Analogues of GABA. XIV. Synthesis and Activity of Unsaturated Derivatives of 5-Aminopentanoic Acid (d-Aminovaleric Acid)
Authors: Allan RD , Dickenson HW , Johnston GAR , Kazlauskas R , Tran HW
Published: September 2010

The (Z) and (E) pairs of 5-aminopent-2-enoic acid and 5-aminopent-3- enoic acid, as well as the related 5-aminopent-3-ynoic acid, have been prepared for structure-activity studies on GABA receptors. Only the (Z) isomers were active as GABA agonists with (Z)-5-aminopent-2-enoic acid being two- to four-fold more active than 5-aminopentanoic acid.
The nitration of 4-Nitro- and 4-Bromo-2,6-dimethylphenols; X-Ray Crystal Structures of t-6-Hydroxy-2,6-dimethyl-r-2,4,t-5-trinitrocyclohex-3-enone, r-2,t-6-Dihydroxy-2,6-dimethyl-4,t-5-dinitrocyclohex-3-enone and 4-Bromo-t-6-hydroxy-2,6-dimethyl-r-2,t-5-dinitrocyclohex-3-enone
Authors: Hartshorn MP , Readman JM , Robinson WT , Vaughan J , Whyte AR
Published: September 2010

The nitration of 2,6-dimethyl-4-nitrophenol (1b), with either fuming nitric acid in acetic acid or nitrogen dioxide in dichloromethane, gives the C2-epimeric hydroxy trinitro ketones (4) and (5), the dinitro phenol (6) and the dihydroxy dinitro ketone (7). The nitration of the 4-bromo phenol (1c) is accompanied by some nitro- debromination and compounds (4), (5) and (13)-(17) are isolated. X-ray structure determinations are reported for compounds (5), (7) and (14).
Phase-Behavior of Carbon-Dioxide and Hydrocarbon Mixtures
Authors: Sadus RJ , Young CL
Published: September 2010

Upper critical solution
temperatures, gas-liquid critical temperatures and solubility data of carbon dioxide and hydrocarbon mixtures have been used to obtain a parameter, ξ, characterizing the interaction between pairs of unlike molecules in the mixture. The calculation of ξ values involved the use of the van der Waals one-fluid model together with the Guggenhiem and Redlich-Kwong equations of state. There is a discrepancy of several percent between ξ values calculated from the three sources of data. Trends in the value of ξ are discussed briefly.
Central-Nervous-System Active Compounds .XVI. Some Chemistry of 6-Oxo Caprolactams Derived From an Enamine Ring-Expansion Synthesis
Authors: Heinicke GW , Morella AM , Orban J , Prager RH , Ward AD
Published: September 2010

Several 6-oxo caprolactam derivatives have been prepared by the ring- expansion of enaminopyrrolidones with dimethyl acetylenedicarboxylate . Other acetylenic systems did not react. The products exist in the enol form of the β- keto ester system are are very resistant towards hydrolysis. They react with hydrazine and phenylhydrazine to form pyrazolo [3,4-c] azepinones in low yield. Many of the caprolactams and their pyrazolo -fused derivatives show central nervous system activity of a depressant nature in mice.
Anisotropic Polarizabilities of Tin(IV)-Containing Groups
Authors: Allen GW , Armstrong RS , Aroney MJ , Pierens RK , Skamp KR
Published: September 2010

Electric birefringences , dipole moments and refractivities are reported for a series of organotin compounds. From these are deduced molecular polarizability anisotropies which, with data from Raman band intensities, can be dissected to give the anisotropic polarizabilities for component tin-containing groups. The results fit reasonably within a 'valence-optical' scheme of group polarizability additivity. Regular trends are observed in the directional polarizabilities of groups containing the Group 4b elements Si, Ge and Sn.
1H N.M.R Studies of High-Spin Complexes of Soybean Leghemoglobin. Interactions Between the Distal Histidine and Acetate, Formate and Fluoride Ligands
Authors: Trewhella J , Appleby CA , Wright PE
Published: September 2010

High-resolution 1H n.m.r . spectra have been measured for the acetate, formate and fluoride complexes of ferric soybean leghaemoglobin a. The chemical shifts of the resolved ow-field haem resonances are very sensitive to pH, reflecting titration of a group, assigned as the distal histidine, with pKa 7.1, 7.3 and 6.2 for the acetate, formate and fluoride complexes respectively. The magnitude of the pH-induced resonance shifts indicates direct interaction between the distal histidine and the axial ligand . The hyperfine shifted resonances of ferrous deoxyleghaemoglobin, in which no sixth ligand is expected, are insensitive to pH over the range pH 5.5-9.3. Evidence for conformational mobility of the distal histidine is presented.
The Chemistry of Pyrrolic Compounds. LVIII. meso-substituted Porphyrins. Further Observations on the Oxidative Cyclization of Bilenes-b
Authors: Clezy PS , Duncan MW , Ravi BN , Vanthuc L
Published: September 2010

The oxidative cyclization of a series of bilenes -b carrying substituted methyl groups at a terminal site (1d-i) has been investigated as an approach to the synthesis of meso-substituted porphyrins . Although in most cases the required porphyrin was formed the yield was generally low and the sequence complicated by the presence of by-products. The usefulness of this procedure as a route to meso -substituted porphyrins is therefore limited although the identification of the by-products has increased our general understanding of the mechanism of the oxidative cyclization.
The Chemistry of Pyrrolic Compounds. LIX. The Oxidative Cyclization of Bilenes-b Substituted by Ethyl or Propyl Groups at a Terminal Site
Authors: Clezy PS , Ravi BN , Thuc LV
Published: September 2010

Oxidative cyclization of bilenes -b substituted with an ethyl or propyl group at one terminal site and a formyl equivalent at the other yields substantial quantities of the meso-ethyl- or meso-propyl-porphyrin. The origin of these meso-substituents has been substantiated by a study of a deuterated analogue. The copper chelate of the meso-ethylporphyrin (2d) seems unexpectedly stable in acid allowing the formation of by- products involving the interaction of the meso-substituent and the adjacent ring ester.
Diels-Alder Reactions With Unsaturated Sulfoxides. Reactions of (Z)-3-Phenylsulfinylprop-2-Enoic Acid and Methyl-Ester With Furan, 1,3-Diphenylisobenzofuran and Anthracene
Authors: Picker K , Proust SM , Ridley DD
Published: September 2010

Methyl (Z)-3-phenylsulfinylprop-2-enoate undergoes Diels -Alder reactions with furan, 1,3-diphenylisobenzofuran and anthracene but chemical and stereochemical courses of the reactions are very dependent upon reaction conditions. Thus, with furan, cis,endo - and cis,exo - adducts are formed exclusively; with 1,3-diphenylisobenzofuran cis,endo - and cis,exo -adducts are formed at low temperatures, whilst the corresponding trans-adducts are formed upon heating; with anthracene where high temperatures are required for condensation cis- and trans-adducts arise together with products from further thermal reactions.
Elimination-Reactions of Stilbene Dibromides. Debromination by Cyanide, Chloride, Iodide or 4-Nitrothiophenoxide Ions in Dimethylformamide
Authors: Avraamides J
Published: September 2010

Transition state structures for debromination reactions of a series of para-substituted stilbene dibromides were evaluated from kinetic and product distribution data for the nucleophiles chloride, cyanide, iodide and 4-nitrothiophenoxide in dimethylformamide . The debrominations appear to utilize transition states in which nucleophilic attack is at bromine despite the strong carbon- nucleophilicity of some of the bases. Products are largely those derived from anti- debromination with all nucleophiles and reactivity is in the order 4-nitrothiophenoxide > cyanide > iodide > chloride.
Fused Heterocycles From Pyrrolethiols. Thieno[2,3-B]Pyrroles, Thieno[3,2-B]Pyrroles and Thiazolo[3,2-a]Pyrroles From Pyrrol-2-Yl Phenacyl Sulfides
Authors: Harris RLN , Mcfadden HG
Published: September 2010

A reinvestigation of the cyclization of pyrrol-2-yl phenacyl sulfides in polyphosphoric acid has shown that the major product is a thieno[3,2-b]pyrrole, where rearrangement of the sulfur substituent from position 2 to position 3 has preceded cyclization. When TiCl4 is used as cyclocondensation reagent minimal rearrangement is observed and the product obtained is either a thiazolo[3,2-a]pyrrole when the pyrrole nitrogen is unsubstituted, or a thieno[2,3-b]pyrrole where an N-substituent is present.
Binuclear Copper(II) Complexes of Some Tetradentate Pyridyl Phthalazine Ligands. Structure, Electrochemistry and Magnetism - Crystal-Structure of Aqua-µ-[1,4-Di-(4',6'-Dimethylpyridin-2'-Ylamino)-Phthalazine-N1',µ-N2 ,µ-N3,N1'']-µ-Hydroxo-Dinitratodicopper(II) Nitrate
Authors: Mandal SK , Woon TC , Thompson LK , Newlands MJ , Gabe EJ
Published: September 2010

The molecular structure of aqua-μ-[1,4-di(4′,6′-dimethylpyridin-2′- ylamino )phthalazine-N1′,μ-N2,μ-N3,N1′]-μ- hydroxo-dinitratodicopper (II) nitrate has been determined by single-crystal X-ray diffractometry . The compound is triclinic, space group Pī , with two molecules in the unit cell of dimensions a 7.8064(11), b 12.9137(14), c 14.8564(14), α 69.857(8), β 80.074(10), γ 83.659(11). The structure was refined by least-squares to a residual of 0.057 for 2806 reflections. The binuclear centre in the complex involves a five-coordinate and a tetragonally distorted six-coordinate copper atom, each with a coordinated, bidentate nitrate, a
copper-copper separation of 3.156 Ǻ and a Cu-O(H)-Cu bridge angle of 113.7°. This complex, and other related systems, exhibit low room-temperature magnetic moments (< 1.2 BM), suggesting antiferromagnetically coupled binuclear copper centres , and in the case of the complex [Cu2( paps )(OH)Cl3].3H2O variable- temperature magnetic data indicate moderately strong exchange with -2J = 432 cm-1. Very high redox potentials are observed for these complexes [0.00-0.83 V (v. s.c.e .)] involving two-electron transfer in one step or two separate steps.
The Reactions of 11 Compounds of Copper, Silver and Chromium With the Molten Lithium-Sodium-Potassium Carbonate Eutectic
Authors: Salarzadeh I , Tariq SA
Published: September 2010

The reactions of Cu2Cl2, CuCl2, AgCl , AgNO3, CrCl2, CrCl3, Cr2O3, K2CrO4, K2Cr2O7, K2Cr3O10 and CrO3 with the molten lithium-sodium-potassium carbonate eutectic were investigated under argon as well as carbon dioxide atmospheres. Copper(I) and copper(II) chlorides reacted to produce CuO with the evolution of CO and CO2 respectively. The silver compounds reacted to produce silver metal and a mixture of O2 and CO2. Chromium(II) and chromium(III) chlorides and Cr2O3 were converted into alkali-metal chromate(III) species. Potassium chromate(VI) was found to be stable in the eutectic. Chromium(VI) oxide, dichromate(VI) and trichromate (VI) accepted oxide ions from the carbonate eutectic, and were ultimately converted into chromate(VI). Carbon dioxide was evolved in all the reactions of the chromium compounds; however, the CrCl2 reaction produced a mixture of CO and CO2. The temperature ranges of the reactions and their stoichiometries were established.
Molybdenum Binding by Pseudomonas aeruginosa
Authors: Stojkovski S , Magee RJ , Liesegang J
Published: September 2010

The uptake of molybdenum by certain bacteria hinders its role as a trace metal in the micronutrients for plant growth. The binding of molybdenum by the Gram-negative bacterium Pseudomonas aeruginosa, PAO1, has been investigated. A molybdenum complex of uronic acid, which forms in the extracellular polysaccharide layer (slime), was isolated and characterized by a variety of techniques. Comparisons with 'mimic' compounds of uronic acids suggest that Pseudomonas aeruginosa, PAO1, produces a binuclear, di-oxo-bridged magnesium salt MgMo2O4(C6H8O7)2.5H2O; this indicates the important role of uronic acids in metallic uptake by bacteria.
Electron-Paramagnetic-Res Spectra of Cu2+ Doped Potassium Tetranitroplatinate(II)
Authors: Duggan LL , Hitchman MA
Published: September 2010

The e.p.r . spectrum of Cu2+ doped into single crystals of K2Pt(NO2)4 is reported. In contrast to the host lattice, which contains four nitrogen-bonded nitrite groups, superhyperfine structure due to coupling with the nitrogen nuclear spins suggests that the guest Cu(NO2)42- complex contains two nitrites bonded through nitrogen, and two coordinated through oxygens probably asymmetrically chelated . The likely structure and orientation of the copper(II) complex is discussed, and the g and A tensors are interpreted in terms of the ground-state wavefunction parameters.
The Oxidation of 1,8-Cineole by Pseudomonas flava
Authors: Carman RM , Macrae IC , Perkins MV
Published: September 2010

Growth experiments of Pseudomonas flava, with cineole and various metabolites of cineole as the sole carbon and energy sources, yielded results which require alterations to a scheme by which P. flava is proposed to utilize these compounds. The optical purity of the metabolites obtained from achiral cineole has been reinvestigated.
Simulated Dynamics of Photochemical Water Splitting
Authors: Lenoir PM , Kozak JJ , Ebbesen TW
Published: September 2010

The evolution of a photochemical water splitting system under continuous irradiation is analysed by numerical simulation for various kinetic and thermodynamic conditions, up to atmospheric pressures of H2 and O2. The analysis shows that it will often be very difficult to interpret experimentally the effect of one variable on the evolution of the system owing to variations in the latency period and the time at which the system reaches a photostationary state. Furthermore, the standard components of sacrificial systems, such as the sensitizer Ru ( bpy )32+ and the electron acceptor methyl viologen , are found to be very ill-suited for a complete photoconversion system. The key problem of poor performance is the fact that intermediate species generated by the system become majority species. These broad conclusions are quantified by our simulations and the benefits and drawbacks of various optimization procedures are presented.
Synthesis of (S)-N-(2,3-Dihydroxy-3-Methylbutyl)Acetamide
Authors: Eichholzer JV , Macleod JK
Published: September 2010

The absolute configuration of naturally occurring N-(2,3-dihydroxy-3- methylbutyl ) acetamide, from Verbesina enceloiodes, has been established by synthesis of the (S)-enantiomer.
Theoretical Prediction of CH3O and CH2OH Gas-Phase Decomposition Rate Coefficients
Authors: Greenhill PG , Ogrady BV , Gilbert RG
Published: September 2010

Theoretical predictions are made for the pressure and temperature dependences of two reactions involved in methanol combustion: (A) CH3O → CH2O + H and (B) CH2OH → CH2O + H. The calculations are carried out by using RRKM theory with a Gorin model for the activated complexes, with fall-off effects being taken into account by using the master equation. Results for the high-pressure rate coefficients (s-1) are (A) 3×1014 exp(-108 kJ mol-1 /RT), (B) 7×1014 exp(-124 kJ mol-1 /RT) at 1000 K. For the low-pressure limiting rate coefficient (cm3 s-1) over the range 600- 1000 K (A) 8×10-9 exp(-90 kJ mol-1 /RT); (B) 2×10-8 exp(-108 kJ mol-1 /RT). At 1000 K, the pressure at which the fall-off rate coefficients are one-half of their limiting high-pressure values are 3x108 Pa for both reactions. Formulae for inclusion of these reactions (including fall- off effects) over the range 300-2000 K and 10-2-106 Pa in modelling complex kinetic schemes are presented.
The Rates of Gas-Phase Reactions of Solvated Anions With Acetone and Methyl Acetate. A Flowing Afterglow Study
Authors: Bowie JH , Hayes RN , Sheldon JC , Depuy CH
Published: September 2010

The gas-phase reactions of MeO ---- HOMe with acetone and methyl acetate to form solvated enolate anions have rates of 2.0×10-9 and 4.8×10-11 cm3 molecule-1 s-1. It is proposed that the latter reaction is slow because internal barriers (transition states more negative in energy than reactants) cause the reactants to be entropy- favoured. Rates of reaction decrease dramatically as the extent of solvation of the nucleophile is increased; e.g., for the reactions of MeO -( HOMe )n(n = 1- 3) with acetone, the rates for n = 1-3 are 2.0×10-9, 1.5×10-10 and 1.6×10-12 cm3 molecule-1 s-1, respectively.
Stabilization of Simple Imines by Coordination to Ruthenium(II), and Aspects of Their Reactivity
Authors: Whebell GW , Keene FR
Published: September 2010

The oxidation of a number of secondary amines coordinated to ruthenium(II) was investigated. Pyrrolidine (1) and piperidine (5) formed the corresponding 1-imines [1-pyrroline (2) and 2,3,4,5- tetrahydropyridine (6)]; these complexes were stable, although spectral and electrochemical properties show there to be only minor π-back- bonding between the RuII metal centre and the imine ligands. The analogous β-unsaturated amines [3-pyrroline (3) and 1,2,3,6- tetrahydropyridine (7)] complexes also underwent oxidative dehydrogenation reactions, and in these cases produced the corresponding aromatic species [pyrrole (4) and pyridine (8), respectively]. Coordinated N-methylallylamine (9) was oxidized to a mixture of the two possible 1-imine species (10) and (11), and preliminary studies indicated that the 1-aza 1,3-diene (11) product would undergo a Diels-Alder reaction while attached to the metal centre.
2,2',4,4',6,6'-Hexanitrobiphenyl-3,3',5,5'-Tetramine: Synthesis and Comparison of Physicochemical Properties With Those of Other Amino Nitro Biphenyls
Authors: Bell AJ , Eadie E , Read RW , Skelton BW , White AH
Published: September 2010

A synthesis of 2,2′,4,4′,6,6′-hexanitrobiphenyl-3,3′,5,5′-tetramine, the most highly aminated of a series of hexanitrobiphenyl explosives, is described, and its physical and spectroscopic characteristics determined. The thermal properties and impact sensitiveness of the explosive have been studied, and the substance has been found to be relatively unstable to heat and more sensitive to impact than expected by comparison with other aminated polynitroaromatic compounds. Evidence is provided which suggests that, contrary to present understanding, the introduction of amino groups into such nitroaromatics may decrease their thermal stability and lower their chemical stability sufficiently to allow partial decomposition at low impact energies. �The structure of the tetramine has been determined by X-ray crystallography, and the features likely to be responsible for the unexpected physicochemical properties of the tetramine are discussed based on this.
Synthesis of Casein-Related Peptides and Phosphopeptides. I. Solution-Phase Synthesis and 13C N.M.R.-Spectroscopy of the N-α-Acetyl Octapeptide N-Methylamide Corresponding to Region 14-21 of Bovine β-Casein A2
Authors: Perich JW , Alewood PF , Johns RB
Published: September 2010

The octapeptide, Ac-Glu-Ser-Leu-Ser-Ser-Ser-Glu-Glu-NHMe (I), was synthesized by the solution-phase method by using the mixed anhydride coupling procedure for the fragment condensation of the Nα-acetyl tripeptide, Ac-Glu(OBut)-Ser(But)-Leu-OH, with the pentapeptide N-methylamide hydrochloride, Cl.H2-Ser(But)-Ser(But)-Ser(But)-Glu(OBzl)-Glu(OBzl)-NHMe, followed by palladium-catalysed hydrogenolysis of Ac-Glu(OBut)-Ser(But)-Leu-Ser(But)-Ser(But)- Ser(But) Glu(OBzl)Glu(OBzl NHMe in trifluoroacetic acid. The synthesis of the two peptide fragments was accomplished in high yields and purity by using the repetitive excess mixed anhydride procedure and the isobutoxycarbonyl mixed anhydride of acetic acid for the rapid and high yielding N-acetylation of the tripeptide fragment. 13C n.m.r. spectroscopy was routinely used to monitor the efficiency of the coupling steps and to confirm the structure of octapeptide (1), signal assignments being possible for both the protected tri- and penta-peptides.
The Chemistry of Eremophila spp. XXVII. A New Lignan From E. dalyana
Authors: Ghisalberti EL , Jefferies PR , Skelton BW , White AH
Published: September 2010

The structure of a new lignan isolated from Eremophila dalyana F. Muell . has
been determined to be (-)-3,6-bis-(3,4-dimethoxyphenyl)tetrahydro-1H,3H-furo[3,4c]furan-1,4-diol by spectroscopic and X-ray crystallographic methods.
Phenyl Tetraacetic Acid Ligands for Gadolinium: Potential Magnetic-Resonance Image Enhancing Agents
Authors: McLaren AB , Baker RJ , Wilson JG
Published: September 2010

Three new ligands suitable for chelation to gadolinium have been synthesized. N,N'- (1,2-Phenylenebis[imino(2-oxoethane-2,l-diyl)])bis[N-(carboxymethyl)glycine] and N,N'-(1,3-phenylenebis[imino(2-oxoethane-2,l-diyl)])bis[N-(carboxymethyl)glycine] were prepared from the corresponding phenylenediamines and N,N'-[1-(4-methylpheny1)ethane-1,2-diyl]bis[N-(carboxymethyl)glycine] from 4-methylbenzaldehyde. Attempted syntheses of other para derivatives of the latter compound produced only oxopiperazinediacetic acids.
The Nature of the Hexahydrates of Divalent Transition Metal Cations: The Structures of the Hexafluorogermanate Hexahydrates of Iron(II), Cobalt(II) and Nickel(II)
Authors: Hoskins BF , Linden A
Published: September 2010

The crystal and molecular structures of the room temperature phases of MII(H2O)6GeF6 (M = Fe, Co, Ni) are reported. In each structure the M(H2O62+ and GeF62- octahedra are in approximate CsCl -type packing with hydrogen bonding between the ions. Differences in the structures arise from disorder in the orientations of the octahedra . Fe(H2O)6GeF6 crystallizes in the spate group R3M, with three molecules in the unit cell of dimensions ahex , 9.728(2), Chex 9.796(2) �. Refinement converged with R 0.0135 and Rw 0.0137, 286 independent observed reflections being used. There is disorder of both fluorine and oxygen atoms between two positions related by a mirror plane, which raises the 3 symmetry within each octahedron to overall 3m symmetry. Ni(H2O)6GeF6 crystallizes in the spate group R3 with three molecules in the unit cell of dimensions ahex 9.443(1), chex 9 .77O(l) �. Refinement converged with R 0.016 and R, 0.018 for 444 independent observed reflections. There is disorder only of the fluorine atoms between two positions unrelated by any symmetry element. CO(H2O)6GeF6 crystallizes in the space group P21/c with two molecules in the unit cell of dimensions a 6.552(2), b 9.577(2), c 8.520(1) �, ,β 99.74(2)�. Refinement converged with R 0.042 and R, 0.054 for 1232 independent observed reflections. The structure is not disordered and deviates only slightly from rhombohedral symmetry.
An E.S.R. Investigation of Ethoxy and Trimethylsilyloxy Iminyl Radicals
Authors: Glover SA , Beckwith ALJ
Published: September 2010

Trimethylsilyloxy and ethoxy iminyls (4a-i) have been generated by photolysis of solutions of the corresponding trimethylsilyl and ethyl N- chloro imidates , in the cavity of an e.s.r. spectrometer. The unpaired electron resides in a 2py orbital on nitrogen in concurrence with the results of MNDO and INDO calculations. The bimolecular rate constants for decay of trimethylsilyloxy t-butyl iminyl (4c) have been evaluated. Trimethylsilyloxy 1,l-dimethylbut-3-enyl iminyl (4e) undergoes an N-C δ cyclization.
The Photoelectron Spectra the Chloro Toluenes
Authors: Peel JB , Vonnagyfelsobuki EI
Published: September 2010

The HeI and HeII photoelectron spectra of the chloro toluenes have been measured. The spectra are assigned using HeI/HeII cross-section ratios and a composite-molecule model within an ab initio valence-electron-only model potential (VEOMP) framework. The order of the first two ionization potentials for the chloro toluenes is assigned as πS < πA which is contrary to the VEOMP assignment for benzal chloride and benzotrichloride , but is consistent with linear correlations using group electronegativities and σI scales. Furthermore, linear correlations using the first two ionization potentials of fluoro and chloro toluenes with group electronegativities are shown to be a useful aid in spectral assignment and, moreover, suggest that for benzyl fluoride and benzal chloride the most appropriate σI values are 0.20 and 0.31 respectively.
Gliotoxin-E: A New Biologically-Active Epipolythiodioxopiperazine Isolated From Penicillium terlikowskii
Authors: Waring P , Eichner RD , Tiwari-Palni U , Mullbacher A
Published: September 2010

The trisulfide analogue (1; n = 3) of gliotoxin (1; n = 2) has been purified and characterized from cultures of Penicillium terlikowskii , and has also been shown to be present in cultures of the pathogenic fungus Aspergillus fumigatus and the thermophilic fungus Thermoascus crustaceus. This compound is equipotent with gliotoxin in a macrophage cell adherence assay confirming earlier results on crude preparations of the compound from A.fumigatus . The compound has been named gliotoxin -E by analogy with sporidesmin-E.
Oxidation of Isomuellitol and Hexahydromuellitol With Chromium Trioxide
Authors: Fazldeen H
Published: September 2010

Chromate oxidation of isomuellitol (2) led cleanly to the production of a cyclic trione , 2,2,9,9,15,15-hexamethyl- 1,8,14-trioxatrispiro [4.1.4.1.4.l]octadecane-6,12,18-trione (4), but the product derived from hexahydromuellitol (3) was an unexpected γ-lactone, 4-hydroxy-2,4-bis(3′-methylbutyl )-3-(4″-methyl-1″-oxopentyloxy)-5-oxotetrahydrofuran-2-carboxylic acid (5).
Heterocyclic-Derivatives of Guanidine. VI. Formation and X-Ray Structure Determination of 2-Dimethylamino-7,8-diphenyl-4,6-dihydropyrrolo[1,2-a]pyrimidine-4,6-dione
Authors: Banfield JE , Fallon GD , Gatehouse BM
Published: September 2010

The structure N-(2-dimethylamino-4-oxo-7,8-diphenyl-4,6-dihydropyrrolo [l,2-a]pyrimidi n-6-yl-idene)acetamide (3) is proposed for a compound derived from the action of ketene on 2-(2-imino- 3,4-diphenyl-2H-pyrrol-5-yl)-1,1,3-trimethylguanidine (1; R1 = R2 = R3 = Me) on the basis of the crystal structure of its hydrolysis product, the oxo-compound 2-dimethylamino-7,8-diphenyl-4,6-dihydropyrrolo[l,2-a]pyrimidine-4,6-dione (4), the structure of which was determined by X-ray analysis. A lower homologue of (3), N-(2-methylamino-4-oxo-7,8-diphenyl-4,6-dihydro- pyrrolo[l,2-a]pyrimidin-6-ylidene)acetamide (2), and some related compounds are described.
The Crystal and Molecular Structure of trans-Dichloro-mer-tris(dimethylphenyl-phosphine)hydridoiridium(III) by X-Ray and Neutron Diffraction
Authors: Robertson GB , Tucker PA
Published: September 2010

The crystal and molecular structure of mer -(PMe2Ph)3H- trans-Cl2IrIII (1) has been determined by single-crystal X-ray and neutron diffraction analyses. Crystals are monoclinic, space group P1, with a 8.91 9(4), b 9.895(4), c 12.269(6) �, α 70.33(4), β 81.75(4), γ 88.26(4)�, Z 2. The structure was solved by conventional heavy atom methods and refined by full-matrix least-squares analyses to final R values of 0.067 (X-ray data, R = ∑// Fo/-/Fc2/∑Fo/, 7516 independent reflections) and 0.086 (neutron data, R = ∑/Fo2- Fc2/∑ Fo2 2290 independent reflections). Weighted mean values for metal-ligand distances are Ir -P(trans to H) 2.365(2) �, Ir -P(trans to PMe2Ph) 2.329(2) � and Ir -Cl(trans to Cl) 2.402(2) and 2.364(2) �. The iridium-hydrogen bond [1.616(7) �] is trans-lengthened, vis-a-vis Ir -H trans to Cl, by c. 0.05 �. The difference in the mutually trans Ir -Cl bond lengths is ascribed to the inequivalence of intramolecular non-bonding interactions. The Ir -P(trans to PMe2Ph) bond length in (1) is shorter than that in mer -(PMe2Ph)Cl3IrIII. The smaller steric requirement of the hydride ligand in (1) allows the mutually trans phosphines to move away from their cis neighbour. In turn, the phosphines approach the metal more closely to compensate for the decreased phosphine substituent-phosphine substituent non-bonding interactions.
Experiments Directed Towards the Synthesis of Anthracyclinones .XIV. An Intermediate for the Synthesis of Vineomycins
Authors: Cambie RC , Howe TA , Pausler MG , Rutledge PS , Woodgate PD
Published: September 2010

Anthrarufin (4) has been converted by a high-yielding route involving sequential reductive Claisen rearrangements into 1-acetoxy-5-methoxy-9,10-dioxo-6-(2'-oxopropy1)-9,10-dihydroanthracene-2-carbaldehyde (3), an intermediate which is suitable for the synthesis of vineomycins . The thermal Claisen rearrangements of some allyl ethers of 1,5-dihydroxyanthraquinone have been examined.
The Crystal Structure of Acifluorfen {5-[2-Chloro-4-(trifluoromethyl)-phenoxy]-2-nitrobenzoic Acid}
Authors: Kennard CHL , Smith G , Hari T
Published: September 2010

The crystal structure of the herbicide acifluorfen (5-[(2-chloro-4-trifluoromethyl)]phenoxy-2- nitrobenzoic acid] has been determined by X-ray diffraction and refined to a residual of 0.051for 1124 observed reflections. Crystals are monoclinic, space group C2/c with cell dimensions a 26.848(7), b 8 .O29(2), c 19 .Ol4(6) �, ,R l34.72(2)� and Z 8. The molecules form centrosymmetric hydrogen-bonded cyclic dimers [O---0, 2.637(7) �] with the carboxylic acid group and the phenoxy group synclinally related to the first phenyl ring while the nitro substituent isessentially coplanar with the ring.
An Extremely Simple Route to a Prostaglandin Precursor: Hexamethylphosphoric-Triamide-Mediated Conjugate Addition of 1-(Phenylthio)Oct-2-Enyllithium to 4-Tert-Butoxycyclopent-2-Enone and Triphenyltin-Chloride-Assisted Reaction of the Enolate With Methyl 7-Iodohept-5-Ynoate
Authors: Haynes RK , Lambert DE , Schober PA , Turner SG
Published: September 2010

Reaction of 4-t-butoxycyclopent-2-enone with (E)-1-(pheny1thio)oct-2-enyllithium in tetrahydrofuran containing 1.5 equivalents of hexamethylphosphoric triamide at - 78� followed by treatment of the resulting enolate with one equivalent of triphenyltin chloride and then with methyl 7-iodohept-5-ynoate at - 20� gives the vicinally dialkylated cyclopentanone, methyl (a-9-oxo-1l-t-butoxy-13-(phenylthio)prost-14-en-5-ynoate, as a 1 : 1 mixture of diastereomers epimeric at C13, in 70-72% overall yields from the octenyllithium reagent. Stereoselective reduction of the C9 carbonyl, conversion of the sulfide into the allylically transposed alcohol, and removal of the t-butyl group by means of iron(III) chloride in acetic anhydride at 0� provides a triacetate which is converted into racemic methyl 5,6-didehydroprostaglandin F2a methyl ester as a 1 : 1 mixture of diastereomers epimeric at C15.
The Alkaloids of Picrasma javanica
Authors: Arbain D , Sargent MV
Published: September 2010

Extraction of Picrasma javanica B1. (Simarubaceae) has yielded two new P- carboline alkaloids,1-ethenyl-4-methoxy-9 H- pyrido-[3,4-blindol-5-ol (5-hydroxydehydrocrenatine) (4) and l-ethyl-4-methoxy-9H-pyrido[3,4-blindol-5-ol (5-hydroxycrenatine) (5), the structures of which follow from their spectroscopic properties. In addition, the known alkaloids crenatine (2) and dehydrocrenatine (1) were isolated. Attempts to synthesize 1-ethyl-4,5-dimethoxy-9-methyl-9 Hpyrido [3,4-blindole(6) are described.
Synthesis of Polynitro-Substituted 2'-Nitrobiphenyl-2-Amines, Analogs of Polynitro Benzo[c]cinnoline Oxide Derivatives
Authors: Bell AJ , Read RW
Published: September 2010

2',3,4',5- and 2',3,5,6'-Tetranitrobiphenyl-2-amines, and 2',3,4',5,6'- and 2',4,4',6,6'-pentanitrobiphenyl-2-amines, have been synthesized for the first time, along with the known 2,4,8- and 2,4,10-trinitrobenzo[c]cinnoline 6-oxides and 1,3,7,9-tetranitrobenzo [c]cinnoline 5- oxide. The benzocinnoline oxide derivatives were found to have higher densities and thermal stability than those of the corresponding biphenylamines. These observations are discussed in terms of structure.
Substitution Reactions of α-Alkyl 4- and 5-Nitropyrrol-2-ylmethyl Derivatives
Authors: Harsanyi MC , Norris RK
Published: September 2010

The α-t-butyl 4- and 5-nitropyrrol-2-yl chlorides (5b) and (6b) react with azide, thiocyanate and p- toluenethiolate ions in dimethylformamide through cationic species in an SN 1-type process, rather than by the SRNl or SN(AEAE) processes, by which their analogues in the benzene, furan or thiophen systems react. These reactions are so facile that they take place in the aqueous dimethylformamide solutions produced during the workup of reaction mixtures. Solvolysis of (5b) or (6b) in methanol produces high yields of the corresponding methyl ethers (5f) and (6f) The chloride (6b) reacts with methoxide ion to produce the diene (33), which reacts reversibly with excess methoxide to give polymethoxylated derivatives. The mesitoic ester (3d) and the acetic ester (3c) are sufficiently unreactive by the cationic pathway, unlike the highly reactive chlorides (3b) and (4c), to allow reaction with the lithium salt (16) and the tetrabutylammonium salt (17) of 2-nitropropane to occur by an SRNl mechanism to give the C- alkylate (3e).
Lewis Base Adducts of Lead(II) Compounds. I. Polymer Isomerism in Some 1-2 Adducts of Lead(II) Halides With Pyridine Bases
Authors: Engelhardt LM , Patrick JM , Whitaker CR , White AH
Published: September 2010

Recrystallization of lead(II) halides, PbX2 (X = C1, Br, I), from n- methylpyridine, n = 3, 4, yields crystalline 1 : 2 adducts; these have all been shown by single-crystal X-ray structure determination to contain the lead in an essentially octahedral six-coordinate environment, two of the coordination sites being occupied by monodentate pyridine base moieties and four by bridging halogen, yielding infinite polymeric arrays. For X = Cl, Br, n = 3, the nitrogen atoms lie cis in the coordination sphere; for the other complexes, they are trans. In the two cis complexes, distortion from ideal orthogonal geometry is more substantial than in the trans, possibly indicative of the presence of a sterically active 'lone pair'.
Simulated Stern-Volmer Plots for 1-1 Ground-State Complexation
Authors: Blatt E , Mau AWH , Sasse WHF , Sawyer WH
Published: September 2010

Stern-Volmer plots are simulated for the case of static quenching due to 1:1 ground-state complexation of quencher and fluorophore in solution, and compared with previously obtained experimental data. For cases where the association constant KC > 105 dm3 mol-1, upward curvatures of Stern- Volmer plots are expected. When KC is between 103 and 105 dm3 mol-1 linearity is obtained, while for KC < 103 dm3 mol-1 upward curvatures are again predicted. The significance of these results to fluorescence quenching experiments in general is discussed.
Preparation and Structure of Tetraphenylarsonium Bis[1,2-Dicyanoethenedithiolato]oxotechnetate(V)
Authors: Colmanet SF , Mackay MF
Published: September 2010

The reaction of sodium 1,2-dicyanoethenedithiolate with [AsPh4][TcOCl4] in ethanol yields crystals of [AsPh4][ TcO ( mnt )2] (1). Crystals of (1) are monoclinic and belong to the space group P21/c with a 12.636(1), b 13.749(1), c 18.484(1)Ǻ, β 93.49(1)� with Z 4. Refinement on 3669 data measured with Cu Kα radiation converged at R 0.063. The structure consists of [ TcO ( mnt )2]- anions and [AsPh4]+ cations. The technetium(V) atom is five-coordinate with the four sulfur atoms in the basal positions and the oxo ligand in the apical position, to give a distorted square-pyramidal environment about the technetium. The Tc =O bond distance is 1.655(6)Ǻ.
Evaluation of Some Cyclic Dipeptides as Catalysts for the Asymmetric Hydrocyanation of Aldehydes
Authors: Jackson WR , Jayatilake GS , Matthews BR , Wilshire C
Published: September 2010

A series of cyclic dipeptides has been prepared and evaluated as catalysts for the asymmetric hydrocyanation of benzaldehyde and 3-phenoxybenzaldehyde. Cyclo -(R,R)- or (S-S)-( phenylalanylhistidyl ), previously reported by Inoue and his coworkers, has proven to be the most effective catalyst, giving high preparative and optical yields under appropriate conditions.
The Meisenheimer Rearrangement in Heterocyclic Synthesis. IV. Derivatives of the 2H,6H-1,5,4-Benzodioxazocine and 7H-1,6,5-Benzodioxazonine Ring Systems: X-Ray Crystal Structure of 10-Methoxy-5-methyl-7-phenyl-2,3,4,5-tetrahydro-7H-1,6,5-benzodioxazonine
Authors: Bremner JB , Browne EJ , Engelhardt LM , Gunawardana IWK , White AH
Published: September 2010

Meisenheimer rearrangement of the N-oxides (4) derived from a series of 5-aryl-4-methyl-2,3,4,5-tetrahydro-1,4-benzoxazepines (3) gave rise to eight derivatives (5) of the new 2H,6H-1,5,4-benzodioxazocine ring system. Reaction of 9-methoxy-5-methyl-6-phenyl-3,4,5,6- tetrahydro-2H-1,5-benzoxazocine (6) with 3-chloroperoxybenzoic acid gave an unstable N-oxide (7). A Meisenheimer rearrangement product from (7), 10-methoxy-5-methyl-7-phenyl-2,3,4,5-tetrahydro-7 H-1,6,5- benzodioxazonine (8), the first example of this ring system, was isolated directly in moderate yield on oxidation of (6) with cooling. The crystal and molecular structure of (8) has been determined by X-ray crystallographic methods.
The Nitration of 3,4,5,6-Tetramethylbenzene-1,2-Dicarbonitrile, 2,3,5,6-Tetramethylbenzonitrile, 1,2,3-Trimethyl-4,6-Dinitrobenzene and 1,2,4,5-Tetramethyl-3,6-Dinitrobenzene. Methyl Migrations Following ipso-Substitution
Authors: Hartshorn MP , Readman JM , Robinson WT , Sies CW , Wright GJ
Published: September 2010

Nitration of 3,4,5,6-tetramethylbenzene-1,2-dicarbonitrile (1a) gives epimeric pairs of dinitro ketones (6a) and (7a), and hydroxy ketones (9) and (10), in addition to the benzyl nitrate (4) and phthalide (5). Nitration of 2,3,5,6-tetramethylbenzonitrile (11) gives the epimeric dinitro ketones (15) and (16), in addition to the nitrobenzonitrile (12) and the nitrophthalide (13). Nitration of 1,2,3-trimethyl-4,6- dinitrobenzene (17) gives dimethylpropanedioic acid (23), the dinitrobenzoic acid (24), and the hydroxy dienone (25). Nitration of 1,2,4,5-tetramethyl-3,6-dinitrobenzene (18) gives dimethylpropanedioic acid (23), the dinitrobenzoic acid (26), and the nitro dicarboxylic acid (27). The formation of compounds (6a),(7a),(9),(10),(15),(16),(23) and (27) all involve methyl migrations following nitronium ion attack ipso to the migrating methyl group. X-Ray structure determinations are reported for compounds (6a), (9) and (15).
The Reaction of Some o-Nitroazobenzenes With Hydroxylamine
Authors: Wilshire JFK
Published: September 2010

The reaction of some representative o-nitroazobenzenes with hydroxylamine in ethanolic sodium hydroxide solution gave good to excellent yields of the corresponding 2-aryl-2H-benzotriazole 1-oxides. In some cases, the corresponding parent 2-aryl-2H-benzotriazoles were also obtained. Under the same reaction conditions, nitrobenzene was essentially unreactive. It is suggested that the reactive species is diimide.
The Reduction of Some 2,2'-Dinitrodiaryl Compounds and Related Compounds by Thiourea S,S-Dioxide (Formamidinesulfinic Acid)
Authors: Wilshire JFK
Published: September 2010

The reaction of thiourea S,S-dioxide ( formamidinesulfinic acid) in ethanolic alkali with 2,2?-dinitrobiphenyl and several related dinitro compounds possessing an -X-bridge (where X = NH, NMe , O and S), located at the 1,1′-positions, has been investigated. With 2,2′-dinitrobiphenyl ′(which gives good yields of benzo [c] cinnoline and its oxides) and, to a minor extent, with 2,2′-dinitrodiphenylamine, anintramolecular reaction occurred to give heterocyclic products; with each of the other dinitro compounds, the only product obtained was formed as the result of a Smiles rearrangement.
The Deposition of Sulfur on Pyrite and Chalcopyrite From Sodium Sulfide Solutions
Authors: Buckley AN , Woods R , Wouterlood HJ
Published: September 2010

The deposition of sulfur from oxygenated sodium sulfide solutions on to fracture surfaces of massive natural pyrite from two different locations has been studied by X-ray photoelectron spectroscopy. For both samples an overlayer of elemental sulfur was formed from sulfide concentrations between 10-5 and 5×10-2 mol dm-3 with a maximum near 10-2 � mol dm-3; the decrease in sulfur coverage at the higher concentrations is accounted for by polysulfide formation. However, under the same conditions, the sulfur coverage on pyrite from Spain was double that on pyrite from Elba. Although the two minerals contain different levels of trace elements, it was not possible to identify the cause of the difference in behaviour. The incorporation of copper into the surface of the Spanish pyrite decreased the sulfur coverage by a factor of two, indicating that foreign atoms can have a significant effect. The sulfur layer formed on chalcopyrite after immersion in sodium sulfide solutions was about half that on Spanish pyrite treated simultaneously. The significance of these findings to the selective collectorless flotation of chalcopyrite/pyrite ores is discussed.
Zinc Acid Reduction of 2,3,4,5-Tetraalkylpyrroles
Authors: Andersonmckay JE , Lawlor JM
Published: September 2010

The stereo- and regio -chemical course of the zinc/acid reduction of C-tetraalkylpyrroles to pyrrolines and pyrrolidines is strongly influenced by experimental conditions, especially the acidity and the nature of the N-substituent.
The Crystal Structures of the Diastereoisomers (+)589-(Λ-δ-δ)-cis-Bis(ethylenediamine)dinitrocobalt(III)Hydrogen-D-tartrate Monohydrate and (-)589-(Λ-λ-λ)-cis-Bis(ethylenediamine)dinitrocobalt(III) Hydrogen-D-tartrate Dihydrate
Authors: Frederiksen JM , Horn E , Snow MR , Tiekink ERT
Published: September 2010

The crystal structures of the diastereoisomers formed between the hydrogen-D-tartrate anion and the cations (+)-(Λ-[Co(en)2(NO2)2]+ (1) and (-)-(Δ)-[Co(en)2(NO2)2]+ (2) have been determined by three-dimensional X-ray analysis. The crystal structures are comprised of octahedrally coordinated cobalt atoms, hydrogentartrate anions and water molecules interconnected by a complex hydrogen bonding network. In (1), columns of complex parallel to a 21 screw axis along a, are linked via hydrogen bonding contacts to a total of six chains of 'head-to-tail' hydrogentartrate strands. In contrast, in (2) the chains of hydrogentartrate anions associate with each other to form well defined 'walls' which sandwich hydrogen-bonded columns of complex cations such that the structure may be thought of as a layer structure of hydrogentartrate anions and complex cations. Crystals of both compounds are orthorhombic, space group P212121 with Z = 4, unit cell parameters for (1): a 7.670(1), b 12.160(1), c 18.028(1)Ǻ, V 1681.4 Ǻ3 and for (2): a 7.735(2), b 8.505(5), c 26.846(9) Ǻ, V 1766 1 Ǻ3. The structures were each refined by a full-matrix least-squares procedure to final R 0.026, Rw 0.027 for 1764 reflections with I ≥ 2.5σ(I) for (1) and R 0.065, Rw 0.073 for 1322 reflections for (2).
Stabilization of Cobalt(I) by Tripodal π-Acceptor Ligands Py3X (Py=2-Pyridyl; X=N, Ch, COH, P, P=O), and Preliminary Studies on the Reaction of Water and Carbon Dioxide With the Bis(ligand)cobalt(I) Complexes
Authors: Hafeli TA , Keene FR
Published: September 2010

Bis ( ligand )cobalt(III/II) complexes of the tripodal π-acceptor ligands Py3X ( Py = 2-pyridyl; X = N, CH, COH, P, P=O) have been synthesized and characterized. Electrochemical studies in acetonitrile (or propylene carbonate) solution reveal the CoIII/CoII and CoII/CoI redox couples for all complexes on the cyclic voltammetric time scale; coulometry studies show the CoI species for X = CH, P, P=O have long-term stability, while for X = N, COH the analogous complexes may be observed but are not sustained for such long periods (i.e. minutes or hours in the last two cases). Aspects relating to the stabilization of the CoI state by these ligands are discussed. Preliminary studies on the reactivity of the bis(ligand)cobalt(I) species (X = CH, P) with water and HCO3- are also reported: water undergoes reduction to H2 but no reduction of HCO3- occurs. In the water reduction reaction involving the complex with X = P, ligand dissociation does not occur, in contrast to the case for X = CH and for the analogous reaction of [Co( bpy )3]+.