bluuebunny/crossref_metadata_2025_split huggingface dataset:
Second‐sphere Coordination of [Pt(bipy)(NH3)2]2+ by Dibenzo‐crown Ethers. Solution Spectroscopic Studies and the Crystal and Molecular Structures of [Pt(bipy)(NH3)2.dibenzo‐30‐crown‐10] [PF6]2.0.6 H2O and [Pt(bipy)(NH3)2.dibenzo‐24‐crown‐8] [PF6]2
Authors: Colquhoun Howard M. , Doughty Simon M. , Maud John M. , Fraser Stoddart J. , Wllliams David J. , Wolstenholme John B. 
Published: November 2013

AbstractIn addition to hydrogen bonding and Coulombic forces, charge transfer interactions stabilise the 1:1 adducts formed between [Pt(bipy)(NH3)2] 2+ and a series of dibenzo‐3n‐crown‐n (n = 6–12) ethers as evidenced by 1H NMR and UV‐visible spectra in solution and by X‐ray crystal structures (for n = 8 and 10) in the solid state. Mutual diamagnetic (ring current) shielding by the aromatic systems of host and guest results in dramatic upfield shifts of certain aromatic proton resonances on adduct formation, especially when n = 10 or 11. A broad charge‐transfer absorption band at 350 nm attains its maximum intensity at n = 11 though stability constant measurements indicate optimum binding when n = 10. X‐ray diffraction studies reveal that, when n = 8, only one of the crown ether benzo‐rings interacts with the bipyridyl ligand in a charge‐transfer sense. However, when n = 10, the macrocycle is sufficiently large and flexible to allow both benzo‐rings to enter into stabilising interactions with the bipyridyl ligand such that the platinum complex is encapsulated by the host in a U‐shaped cavity.
Nature and Size of Included Guest Molecule Determines Architecture of Crystalline Cyclodextrin Host Matrix
Authors: Saenger Wolfram 
Published: November 2013

AbstractOwing to its annular shape, the cyclic hexasaccharide α‐cyclodextrin (α‐CD) can form inclusion complexes in aqueous solution. If these are crystallized, the guest molecules are invariably accommodated in the cavities of the host. Depending on size and molecular or ionic character of the guest, different crystal modifications are formed belonging to the herringbone or brick‐type cage structures or to the channel structures. Small molecular guests lead to herringbone cages, small aromatic guests crystallize in brick‐type cages whereas ionic and long molecular guests are enclosed in infinite channels. Thus, there is a clear dependence of crystal packing on the physical properties of the guest molecule. Polyiodide cocrystallizes with α‐CD in different channel forms with iodine atoms arranged linearly in the channels. The packing of the channels is in tetragonal, hexagonal or sheet‐like arrays, depending on counterions which are located in voids between the channels. If a α‐CD is replaced by the larger β‐CD (channel diameters 5 and 6.2 Å resp.), polyiodide now adopts a zigzag structure — a clear case of an influence of host matrix geometry on guest configuration.
Design and Synthesis ofα‐Diketones. The Cyclobutane‐1,2‐dione Chromophore: Synthesis, Dienophilic Reactivity and Electronic Properties of Cyclobutenedione and Polycyclic Cyclobutanediones [1]
Authors: Albert Bernhard , Heller Constanze , Iden Rudiger , Martin Georg , Martin Hans‐Dieter , Mayer Bernhard , Oftring Alfred 
Published: November 2013

AbstractA new synthesis of cyclobutenedione(1)is described. It is found that the tricyclic cyclobutanedione3splits into1and cyclopentadiene if subjected to flash pyrolysis conditions. The dienophilic reactivity of 1 allows the construction of various polycyclic cyclobutanediones, such as3–5and12–14.Other new polycyclic diones, like9–11, 15and16are prepared by means of the acyloin condensation. The low stereoselectivity of1with cyclopentadiene is compared with the selectivity of other cyclobutenes, and the results are placed in the context of secondary interactions and steric hindrance. The unusual colour properties of these diones, from colourless1to blue6are investigated by means of photoelectron spectroscopic measurements and semi‐empirical calculations (MNDO, HAM/3, CNDO/S‐CI).
Characterization of Several Metalloporphyrins in Unusual Oxidation States. The Effect of Axial and Equatorial Ligands
Authors: Cocolios P. , Kadish K.M. 
Published: November 2013

AbstractThe effect of axial and equatorial ligands on the generation of unusual oxidation states in metalloporphyrins is discussed. Selected examples have been taken from the literature. These include the generation of Ni(III) and Ru(III) porphyrins from Ni(II) and Ru(II) complexes containing specific axial and equatorial ligands as well as the generatoin of a Cu(I) metalloporphyrin dianion which is produced upon the overall three‐electron reduction of Cu(II) tetracyanoporphyrin. Special emphasis is placed on the oxidation and reduction of σ bonded iron phenyl porphyrins. These complexes, which are stable as Fe(III), may be oxidized by a single electron to yield unstable compounds characterized as containing a great deal of Fe(IV) character, or reduced by a single electron to produce stable species which resemble, in part, radical anions of Fe(III). This singly deduced species may be described by a resonance equilibria between an Fe(III) porphyrin anion radical and an Fe(II) porphyrin anion. Likewise, the singly oxidized complex may be described by a resonance equilibria between an Fe(IV) porphyrin cation and an Fe(III) cation radical.
Metal—Metal Triple Bonds Possessing the Electron‐Rich σ2π4δ2δ*2 Electronic Configuration
Authors: Walton Richard A. 
Published: November 2013

AbstractThe structural and reaction chemistry of dimetal complexes containing metal—metal triple bonds of the electron‐rich type (σ2π4δ2δ*2 configuration) is reviewed. Metal cores possessing this unit are Mo2+2, Re4+2, Ru6+2, and Os6+2, of which only Re4+2 has yet been subject to a detailed study. Emphasis is placed upon the more recent developments in this field.
Synthesis and Properties of Conducting Bridged Macrocyclic Metal Complexes
Authors: Hanack Michael 
Published: November 2013

AbstractStacked bridged macrocyclic metal complexes of the type shown in Fig. 1A, with pyrazine and 1,4‐diisocyanobenzene as the bridging ligands L, phthalocyanine (Pc) and tetrabenzoporphyrine (TBP) as the macrocycle (Mac), and Fe and Ru as the central metal atoms M, are doped with iodine. The properties and conductivities of the doped compounds [MacML]n are reported. The synthesis and properties of type‐B polymers (Fig. 1B) ([PcMCN]n, M = Co, Rh, Fe, Mn, Cr) with CN as the bridging ligand are described. With Co and Fe these polymers show room temperature conductivities around 10−1 S/cm without doping, which are in the same range as the iodine doped [PcML]n‐compounds. [PcCo(SCN)]n and [TBPCoCN]n are additional examples of type B polymers.
Cyclophanes, XXIII [1] [2.2] Indenophanes — Building Blocks for Novel Multilayered Organoiron Complexes
Authors: Hopf Henning , Raulfs Friedrich‐Wilhelm 
Published: November 2013

AbstractA general approach for the synthesis of [2.2] indenophanes is described employing readily available mono‐(8, 13) and bis‐formyl[2.2]paracyclophanes (20, 21) as substrates. The anellated five‐membered ring is introduced by a multistep sequence involving Wittig‐Horner chain elongation of the different aldehydes, saponification, catalytic hydrogenation, acid‐catalyzed ring closure, and dehydration. In this manner the novel indenophanes 11, 16, 17, 26, and 27 have been synthesized in good yields. The first representatives of a novel class of extended metallophanes, the multilayered ferrocenophanes 32 and 34, have been prepared from 11 and 28, respectively, via their sodium salts 29 and 33. The effect of an anellated [2.2] paracyclophane unit on the proton chemical shifts of the model compounds 30, 31, and 35 is discussed.
Molecular Design of Specific Uranophiles
Authors: Tabushi Iwao , Kobuke Yoshiaki 
Published: November 2013

AbstractMolecular design of uranyl specific ligands is reviewed. Basic principles to characterise the unique nature of uranyl complexes are scrutinized from ligand field caluclations, crystallographic analyses and stability constants of various complexes. The most typical characteristic of uranyl coordination is a planar hexacoordiantion by anionic ligands giving rise to the formation of the “ate‐complex.” Several macrocycles were synthesized by the appropriate combination of these principles. Approaches to recovery of uranium from sea water are briefly reviewed. Organic chelating resins are the most promising candidates for the practical adsorbent.
Structure‐Conductivity Relationship of a Novel Semiconducting Diacetylene Polymer
Authors: Thakur M. , Lando J.B. 
Published: November 2013

AbstractThe crystal structure and electrical conductivity of the polymerized dimer of 1,11‐dodecadiyne has been recently reported. In this article we will present the temperature dependence of the electrical conductivity of this conducting polymer in the undoped state and will probe the structure‐conductivity relationship via a band theoretical approach.
Crystalline‐State Reaction of Cobaloxime Complexes by X‐ray Exposure. XII. A New Type of Racemization with a Negligibly Small Change of the Cell Dimensions [1]
Authors: Tomotake Yasuko , Uchida Akira , Ohashi Yuji , Sasada Yoshio , Ohgo Yoshiaki , Baba ShōE 
Published: November 2013

AbstractCrystals of [(R)‐1‐cyanoethyl] bis(dimethylglyoximato)(diphenylmethyl‐phosphine)cobalt(III), [Co(C3H4N)(C4H7N2O2)2(C13H13P)], on exposure to X‐rays undergo crystalline‐state racemization with a negligibly small change of the cell dimensions. At the initial stage the two crystallographically independent molecules are related by pseudo inversion symmetry in the A2 cell. On X‐ray irradiation to the crystal, the pseudo inversion center becomes a true crystallographic one and the space group becomes A2/a. Both the chiral cyanoethyl groups are converted to the disordered racemates. The rate of the racemization was measured by the intensity variation of the reflections that should disappear after the racemization. The rate constants at 293 and 343 K are calculated to be 4.81 and 5.07 × 10−6 s−1, respectively, assuming first‐order kinetics. The cavities for the two cyanoethyl groups in the initial structure have the largest volumes known in this and related crystals. The positive correlation between the reaction rate and the volume of the cavity for the reactive group holds good for the present crystal.
Effect of the Structure of Some New Weak‐Base Ion‐Exchange Resins on Anion Selectivity
Authors: Bolto B.A. , Jackson M.B. , Siudak R.V. 
Published: November 2013

AbstractThe selectivity of some poly(N‐substituted diallylamine) ion‐exchange resins and some polyamine ion‐exchange resins prepared from crosslinked polyepichlorohydrin toward the systems SO=4/Cl−, NO−3/Cl− and HCO−3/Cl− was measured. The polyallylamine resins show the usual selectivity behaviour towards SO=4 over Cl− with the affinity of SO=4 increasing with dilution of the solution and decreasing with reducing ionization of the resin, providing equilibrium has been reached. The size of the nitrogen substituent on the resin, the resin capacity (which affects the overall charge density) and the base strength of the resin all influence the resin selectivity. The resin type and the nature of the two ions being exchanged determine the relative importance of each factor. In the systems considered in this paper, apart from the normal factors which affect selectivity, the most noteworthy parameter appeared to be the size of the nitrogen substituent. The selectivity behaviour toward the HCO−3/Cl− system of a polyamine prepared from crosslinked polyepichlorohydrin and aminated with homopiperidine compared favourably with Amberlite IRA 68 in a DESAL‐type process.
Soluble Polychelatogenes for Separation of Actinide Ions by Membrane Filtration
Authors: Bayer Ernst , Eberhardt Hans , Grathwohl Paul‐Anton , Geckeler Kurt 
Published: November 2013

AbstractSeparation of metal ions by functionalized soluble polymers using membrane filtration has been investigated. Actinide elements and members from the transition groups and rare earth elements have been bound to polymeric chelatogenes as a function of pH. Sixteen different polymers and derivatives based on poly(ethylenimine), poly(vinylalcohol), poly(urethane), and poly(acrylic acid) have been studied in terms of their capacity and selectivity. Binding studies and cleavage experiments have been carried out by application of membrane filtration for several metals and polychetatogenes. Finally, the stability of polymers and membranes has been studied and found to be sufficient for selective separation of actinide ions.
Solvent‐Polymeric Membranes for Separation of Li+ From Other Alkali Metal and Alkaline Earth Ions
Authors: Jagur‐Grodzinski Joseph , Schori Ehud 
Published: November 2013

AbstractLithium may be recovered from the Dead Sea brines by a process which combines membrane separation with ion‐exchange. Solvent‐polymeric membranes based on alkyl‐arylphosphates cause selective permeation of lithium ions with Br−3 as counter ions. Addition of the derivatives of neutral “crown” ethers did not improve their performance and an adverse effect, due to the decrease in the fluidity of the membrane system, was observed. Incorporation of ionizable “crown” ethers compatible with the system may, however, be advantageous; pH gradients could act as a driving force for transport of lithium in such systems. Membranes prepared with (2‐ethylhexyl)‐diphenyl phosphate (Santicizer 141) gave the best results from the point of view of selectivity of Li+ transport vs. Mg2+ and Ca2+. Maintenance of ca. 10−3 M concentrations of Br2 in the end‐brine solutions gives optimal membrane performance. No significant change in membrane permeability and selectivity occurred during six months of their operation. Lithium ions in the product solution of the membrane separation process may be further separated from the residual Mg2+ and Ca2+ ions and concentrated up to 1 M by ion exchange processes. Lithium may be precipitated from such solutions, free from alkaline earth ions, as Li2CO3.
The Thermal Rearrangement of 1,2,7‐Trienes
Authors: Huntsman William D. , Li Yong‐Jing , Giannamore Vincent P. 
Published: November 2013

AbstractThe thermal rearrangement of 1,6,7‐nonatriene and 1,2,7‐octatriene at 400°C has been studied. Besides intramolecular [2 + 2] cycloaddition reactions, these hydrocarbons undergo intramolecular ene reactions, furnishing cis‐1‐methyl‐2‐(1‐propynyl)cyclopentane and cis‐1‐ethynyl‐2‐methylcyclopentane, respectively.
A New Multi‐Step Thermal Rearrangement of a Terminal Allene
Authors: Mazur Mark R. , Berson Jerome A. 
Published: November 2013

AbstractThe gas‐phase pyrolysis of 2‐methylhept‐2‐ene‐6‐yne proceeds by two pathways, one of which leads via an acetylene → vinylidene rearrangement to a hypothetical bicyclo[3.1.0]hex‐1‐ene intermediate and subsequently to products derived from the 2‐isopropylidenecyclopentane‐1,3‐diyl biradical. The second pathway leads to 1,2‐dimethyl‐4‐methylenecyclopent‐1‐ene by a multi‐step process involving Cope rearrangement, two successive 1,5‐sigmatropic hydrogen shifts, and the equivalent of intramolecular ene reaction. This mechanism is supported by two separate isotopic labeling experiments.
From Allenes to Cyclic Compounds by Hetero‐Ene Synthesis
Authors: Bertrand M. , Cavallin B. , Roumestant M‐L. , Sylvestre‐Panthet P. 
Published: November 2013

Abstractγ‐ and δ‐allenic carbonyl compounds have been synthesized and submitted to thermolysis. A variety of substituted ring systems are thus easily accessible by intramolecular hetero‐ene synthesis.
Cycloaddition Reactions of Substituted Allenes with Triplet Excited Aromatic Thiones: Product Formation and Reaction Mechanism
Authors: Kamphuis J. , Grootenhuis P.D.J. , Ruijter A.P. , Visser R.G. , Bos H.J.T. 
Published: November 2013

AbstractThe reactivity of substituted allenes H2CCC(R)X towards three triplet aromatic thiones has been investigated. Product analysis reveal the formation of two (2+2)‐cycloaddition products the thietanes3, 4(E + Z) and occasionally of one (4+2)‐cycloaddition product, thiopyran derivative (Z)‐5, generally in high overall yields. Steady state measurements show that electron donating substituents in the allenic system enhance the overall reaction rate. There is little effect of solvent polarity on the reaction rate. The correlation between the relative reaction rates and the first adiabatic ionization energy of the substituted allenes is in accordance with the formation of an exciplex between the excited thione and that π‐bond of the allenic system which is conjugated with the substituent X. From this exciplex two isomeric allylic 1,4‐biradicals (Z)‐8 and (E)‐8 are probably formed. After inter‐system crossing, ring closure gives the thietanes3, (E)‐4, (Z)‐4and/or thiopyran derivative (Z)‐5. The ratio in which3, (E)‐4, (Z)‐4and (Z)‐5are formed is explained by considering electronic and steric factors in the proposed reaction mechanism. Experiments with an optically active allene (+)‐PhC(H)CC(H)Me support the intermediacy of a non‐chiral relatively stable allylic 1,4‐biradical. At infinite allene concentration the quantum yield approaches 1, indicating no energy loss during the reaction. Thus no measurable disproportionation of the allylic biradicals (Z)‐8and (E)‐8occurs.
A Horner‐Emmons Approach to Cumulatrienes
Authors: Macomber Roger S. , Hemling Thomas C. 
Published: November 2013

AbstractReaction of allenic phosphonates of structure (R'O)2P(O)CH′CCR2 with LDA led to ylid‐like carbanions (2) by removal of H′. Intermediate 2 reacted with a variety of ketones (R′2′CO) to give adducts (3) which fragmented to cumulatrienes of structure R′2CCCCR2. The cumulatrienes prepared and their yields were: 4a (RCH3, R′Ph, 43%); 4b (R+RR′+R′(CH2)5, 64%); 4c (R+R(CH2)5, R′Ph, 28%); 4d (RR′CH3, 23%). In two cases, 4a and 4d, the cumulatrienes were complexed with chlorotris (triphenylphosphine)‐rhodium.
Electrophilic Additions to Allenes. VIII. The Kinetics and Mechanism of the Addition of Benzenesulphenyl Chloride to Allenes
Authors: Beaulieu Pierre L. , Morrisset Veronique M. , Garratt Dennis G. 
Published: November 2013

AbstractThe rates of addition of benzenefulphenyl chloride to 62 alkyl substituted allenes have been determined in methylene chloride solution at 24.5°C. The rates of addition span a range of 3.4 × 103 in reactivity. No correlation with the extended Taft equation or variations thereof was found when the rates of all 62 compounds were considered. Partitioned rate constants, wherein each term reflects the relative propensity for attack upon a given π orbital‐lobe of the allenic system, allows one to demonstrate the specific effect of placing an alkyl group in each of three stereochemically distinct positions. Of note is the observation that while the magnitude of the polar effect of an alkyl group changes with the stereochemical location, this magnitude is a constant for methyl, ethyl and isopropyl. The rates reported herein are interpreted in terms of rate‐limiting formation of alkylidenethiiranium ions.
Applications of Phase Transfer Catalysis to Arenediazonium Cation Chemistry
Authors: Gokel George W. , Ahern Michael F. , Beadle James R. , Blum Lorna , Korzeniowski Stephen H. , Leopold Ahuva , Rosenberg David E. 
Published: November 2013

AbstractArenediazonium cations have been known for many years but the synthetic utility has been diminished by their lack of stability and by their proclivity for undergoing sundry side reactions. Arenediazonium BF4 and PF6 salts are generally stable solids, but are relatively insoluble in nonpolar organic media. Crown complexation and other forms of phase transfer catalysis increase solubility and allow numerous synthetic transformations to be conducted in good yield. The yield improvements result from a reduction in competing side reactions rather than any fundamental change in mechanism. The reactions to which the phase transfer technique is successfully applied are diazo coupling, reduction, halogenation, arylation and cyclization. In the latter case, the use of potassium superoxide is sometimes a more efficacious reagent than potassium acetate. The phase transfer approach can be used in the high yield synthesis of arenediazosulfones and arenediazocyanides. The latter undergo cycloaddition with many dienes to yield pyridazine derivatives.
Real and Ideal Relationships between Selectivity, Reactivity and Equilibrium
Authors: Argile A. , Carey A.R.E. , Fukata G. , Harcourt M. , More O'Ferrall R.A. , Murphy M.G. 
Published: November 2013

AbstractReactivity and selectivity are discussed in terms of quadratic rate—equilibrium relationships for reaction series sharing a common intrinsic barrier, notably Marcus' equation. R.D. Levine's emphasis on such reactions as forming a “Brønsted Series” is suggested as a basis for defining “ideal” reactivity behavior. Ideal relationships between selectivity and reactivity and selectivity and equilibrium are derived based on reaction schemes drawing a formal distinction between reagent and substrate. In a simple Brønsted relationship, the reagent varies and the substrate is held constant. In an extended relationship, in which both substrate and reagent vary, the Brønsted series becomes a selectivity “network” or matrix characterized by direct and cross quadratic coefficients reflecting curvature of a free energy relationship and the dependence of selectivity upon rate or equilibrium respectively. In the ideal case, the quadratic coefficients are equal but, in practice, they generally differ. Inspection of the relevant reaction schemes shows that in evaluating the coefficients, there is greater cancellation of experimental and chemical scatter arising from non‐systematic variations in reagent structure for the cross than the direct coefficient; this phenomenon accounts in part for the wider observation of reactivity—selectivity than non‐linear free energy relationships. New measurements are reported for reactions of carboxylic acids with enolate and imine substrates. The results are combined with literature data and plotted as reactivity—selectivity and extended Brønsted relationships. The correlations are satisfactorily considered in the context of departures of real from ideal behaviour.
On the Relation Between Reactivity and Selectivity
Authors: Levine R.D. 
Published: November 2013

AbstractCan one relate in a systematic fashion changes in the nature of the reactants to changes in the magnitude of the reaction rate constant? It is suggested that such correlations can be given a precise meaning and that the inverse correlation high selectivity—low reactivity is indeed valid. What need not always be true is that a single selectivity index (e.g., location of the transition state) suffices to quantitatively describe the correlation. When a single selectivity index does suffice we prove the reactivity—selectivity principle including the Hammond postulate.