bluuebunny/crossref_metadata_2025_split huggingface dataset:
[Cu24S12(PMeiPr2)12], [Cu28S14(PtBu2Me)12], [Cu50S25(PtBu2 Me)16], [Cu70Se35(PtBu2Me)21], [Cu31Se15(SeSiMe3)(PtBu2Me)12] and [Cu48Se24(PMe2Ph)20]: New Sulfur‐ and Selenium‐Bridged Copper Clusters
Authors: Dehnen Stefanie , Fenske Dieter 
Published: July 2007

AbstractReaction of copper(I) acetate with bis(trimethylsilyl)chalcogenides E‐(SiMe3)2 (E = S, Se) in the presence of tertiary phosphines in organic solvents leads to the formation of chalcogenbridged copper clusters in crystalline form. In recent investigations, the following structures were isolated and characterised by X‐ray crystallography: [Cu24S12‐(PMeiPr2)12] (1), [Cu28S14(PtBu2Me)12] (2), [Cu50S25(PtBu2Me)16] (3), [Cu70Se35‐(PtBu2Me)21] (4), [Cu31Se15(SeSiMe3)‐(PtBu2Me)12] (5) and [Cu48Se24(PMe2‐Ph)20] (6). The cluster cores of 1‐6 have new structures or new structural characteristics and go some way towards providing an insight into the mechanisms of cluster formation reactions. With the help of the aforementioned compounds a number of structure principles that govern sulfur‐and selenium‐bridged copper clusters can be formulated.
Oxygen and Nitrogen in Competitive Situations: Which is the Hydrogen‐Bond Acceptor?
Authors: Böhm Hans‐Joachim , Brode Stefan , Hesse Ute , Klebe Gerhard 
Published: July 2007

AbstractIn the design of novel protein ligands one of the major challenges is the replacement of functional groups to modify and improve the binding characteristics. Often nitrogen‐ and oxygen‐containing groups are exchanged, or both atoms occur in a competitive situation. We have investigated the hydrogen‐bonding abilities of oxygen atoms covalently bound to two non‐hydrogen atoms of which at least one is formally assigned to an sp2‐type hybridization. In particular, examples in which such oxygen atoms compete with nitrogen atoms in the same molecular segment have been studied. Based on interaction energies obtained from ab initio calculations for complexes of these molecules with water, the oxygen atoms can be classified as rather weak hydrogen‐bond acceptors; nitrogen atoms present in the same fragment exhibit much stronger interaction energies. The ab initio results are confirmed by the relative frequencies with which oxygen and nitrogen atoms are found to be involved in hydrogen bonding in the crystal structures of organic molecules containing the fragments of interest.
Kinetic and thermodynamic study of the mechanism of reversible intermolecular electron‐transfer reactions between horse heart cytochrome c and a series of cobalt imine complexes
Authors: Meier Martin , van Eldik Rudi 
Published: July 2007

AbstractThe Kinetics and Thermodynamics of the Reversible Outer‐Sphere Electron‐Transfer Reactions between Horse Heart Cytochrome cII/III and [Co(phen)3]3+/2+ and [Co(bpy)3]3+/2+ were studied in detail, in particular as a function of temperature and pressure. It was possible to construct a volume profile for both reactions from the pressure data. The transition state was found to be halfway between the reactant and product states on a volume basis in all studied systems. This is in agreement with the λ≠ parameter estimated from the Marcus theory. For all the systems investigated, the differences in the activation volumes are in good agreement with the reaction volumes determined from spectrophotometric and electrochemical measurements at elevated pressure, and from the difference in the partial molar volumes of the metal complexes. The activation and reaction volumes of the bipyridine system are significantly smaller than those of the corresponding phenanthroline and terpyridine systems. A detailed mechanistic analysis is presented. The results show that the different kinetic and thermodynamic techniques employed complement one another.
Double Subroutine Self‐Assembly; Spontaneous Generation of a Nanocyclic Dodecanuclear Cu1 Inorganic Architecture
Authors: Funeriu Daniel P. , Lehn Jean‐Marie , Baum Gerhard , Fenske Dieter 
Published: July 2007

AbstractThe newly synthesised ligand 2 combines binding components known to undergo specific and distinct self‐assembly processes with Cu1 ions. It complexes Cu1 to form, in almost quantitative yield, a large inorganic architecture 1 made up from four ligand molecules and twelve metal ions. The structure of 1 was ascertained by X‐ray radiocrystallography as well as by NMR spectroscopy and electrospray mass spectrometry. It consists of a macrocycle of nanometric dimension with an external diameter of 28 Å; the central cavity has a diameter of 11 Å, which contains four PF−6 anions as well as solvent molecules. The spontaneous formation of 1 results from a self‐assembly process based on a “program” combining two assembly subroutines, each specific to one of the ligand subunits. Self‐assembly through double or, more generally, multiple subroutines can be used to generate a wide variety of highly complex inorganic supramolecular architectures by combination of two or more assembly processes.
Enantioselective Construction of Highly Functionalized Indoloquinolizines—congeners to Polycyclic Indole Alkaloids
Authors: Lock Ralf , Waldmann Herbert 
Published: July 2007

AbstractIndolo[2,3‐a]quinolizines have been prepared in enantiomerically pure form by a very short and efficient synthetic sequence consisting of a) formation of imines of tryptophan esters, b) their enantioselective reaction with substituted silyloxydienes mediated by a chiral or an achiral boron Lewis acid, and c) subsequent ring closure initiated by conversion of the generated vinylogous amides into vinylogous imidoyl chlorides. With this strategy various substituents can be incorporated directly into the 1‐position of the heterocyclic framework of complex indole alkaloids by the choice of an appropriate silyloxydiene, so that subsequent derivatization of the alkaloid precursor at this position is rendered unnecessary.
Quantum‐Chemical Investigations of Stabilizing Interactions in μ‐Diborylcarbene Dicobalt Complexes with a Planar Tetracoordinate Carbon Atom
Authors: Hyla‐Kryspin Isabella , Gleiter Rolf , Rohmer Marie‐Madelaine , Devemy Jérôme , Gunale Anuradha , Pritzkow Hans , Siebert Walter 
Published: July 2007

AbstractQuantum‐chemical methods have been employed to study the nature of stabilization in dinuclear cobalt complexes of the general formula [{(C5H5)Co}2(μ‐CR12BCBR2R3)] (6) as well as the “antivan't Hoff–Le Bel” configuration of the planar tetracoordinate carbon (ptC) atom of the bridging diborylcarbene ligand 9. Extended Hückel and ab initio Hartree‐Fock calculations have been carried out for the model compounds 6b (R1 = R2 = R3 = H) and 6c (R1 = R2 = H; R3 = C6H5). Ab initio electron deformation density maps and natural population analysis calculations show that complexes 6 are stabilized through push–pull effects by which the ptC experiences π electron density delocalization and σ electron density accumulation. The calculated electronic configuration of the ptC in the free ligand 9b is σ2.978π1.501, and in 6b σ3.944π1.356. Electron density donation from one cobalt atom to an aryl group on the bridging ligand further contributes to the stabilization of the complexes 6.
Adsorption of Ionophores and of Their Cation Complexes at the Water/Chloroform Interface: A Molecular Dynamics Study of a [2.2.2]Cryptand and of Phosphoryl‐Containing Podands
Authors: Varnek A. , Troxler L. , Wipff G. 
Published: July 2007

AbstractWe report molecular dynamics simulations on ionophores of different topologies and on their complexes with alkali and alkaline‐earth cations, with or without counterion, at the water/chloroform interface. As ionophores we consider two phosphoryl‐containing podands (the “chainlike” monopodand MP and the “octopuslike” tripodand TP) and the bicyclic cryptand 222. We find that all the solutes behave as surfactants: they remain adsorbed at the interface, without migrating to bulk phases. Their precise location and solvation depend on the nature and conformation of the ionophore, of the cation and of the counterion. Schematically, two types of solutes can be distinguished, depending on their hydrophilic/hydrophobic character. The first type (cryptand 222 and its complexes, or the [MP⋅K+] complex), which have a hydrophobic exterior, stay on the chloroform side of the interface and are partially hydrated by “water fingers”. The second type (free MP and TP, [MP⋅K+]Pic‐ and [MP⋅Sr2+](Pic‐)2 complexes), which are more hydrophilic, are partitioned to a greater extent between the two liquid phases. The status of the ion pairs at the interface depends on the interplay between cation … anion and anion … solvent interactions. When cation‐anion interactions are strong enough (as in [MP⋅Sr2+](Pic‐)2), the ion pairs remain intimate. Otherwise they dissociate, leading to solvent‐separated ion pairs adsorbed at the interface (in the [222⋅K+] Pic‐ complex) or to the migration of the anion to the water phase (in the [222⋅K+] Cl‐ complex).
Electron Transfer in Dinuclear Cobalt Complexes with “Non‐innocent” Bridging Ligands
Authors: Heinze Katja , Huttner Gottfried , Zsolnai Laszlo , Jacobi Albrecht , Schober Peter 
Published: July 2007

AbstractReaction of tripod cobalt(II) templates [{CH3C(CH2PAr2)3}CoII] with potentially bridging ligands L generates the dinuclear compounds [(tripod)‐Co‐L‐Co(tripod)]2+. With L = oxalate (C2O2‐4) a biscobalt(II) complex (1) is formed, while with L = C6H2O2‐4, the dianion derived from 2,5‐dihydroxy‐1,4=benzoquinone (anilic acid), two‐electron transfer within the dimetallic unit occurs and a biscobalt(III) charge distribution results (2a), as shown by X‐ray structural analyses of 1 and 2a, NMR spectroscopy, and theoretical investigations by the INDO method. Complex 2a exhibits an unusually intense, low‐energy absorption in its electronic spectrum; this is explained with a simple MO model. One‐electron reduction of 2a generates the corresponding mixed‐valence complex, which is highly stabilised through extensive electron delocalisation. Substituents at the 3,6 positions of the bridging ligand (Cl, Br, I, NO2, Me, iPr, Ph; 2b‐h) as well as alkyl substitution at the aromatic rings of the tripod ligands (3, 4) influence the optical and electrochemical properties consistent with the proposed model of charge distribution. Formal replacement of one [(tripod)CoIII]3+ moiety by [CH2]2+ leads to the mononuclear complex 6, which is shown to be a typical [(tripod)CoIII=(catecholato)]+ complex. Therefore the substantially different optical and electrochemical properties of the dinuclear complexes with respect to those of 6 result from strong metal‐metal interactions mediated by the bridging ligand.
Macrocyclic Ethers and Their Inclusion Complexes
Authors: Ratilainen Jari , Airola Karri , Nieger Martin , Böhme Marc , Huuskonen Juhani , Rissanen Kari , Nieger D. R. M. 
Published: July 2007

AbstractThe synthesis and characterisation of eleven new macrocyclic ethers (up to 96‐membered [6+6] gigantocycle) with well‐defined cavities are described. Syntheses of the macrocycles M1–M7 were performed under high‐dilution conditions. A “supramolecular” purification method was used for the small [2+2] macrocycles M3–M7, which separated selectively from the reaction mixture on recrystallisation from a dichloromethane/diethyl ether solution mixture. This proved to be an excellent method for purifying [2+2] macrocyclic ethers containing 1,1‐diphenylmethane moieties, and the separation was nearly quantitative. Molecular inclusion of dichloromethane in the cavities of noncovalently bonded macrocyclic ethers M2–M5 was studied by X‐ray diffraction in the solid state. Additionally, clathrate formation was found for macrocycles M1 (including diethyl ether), M2 (including water), M6 (including benzene) and M7 (including benzene).
Alkyne–Carbene Chelate Complexes of Chromium: Arrested Intermediates in the Benzannulation Reaction and Precursors of Densely Functionalized Centrosymmetric Chrysenes
Authors: Hohmann Frank , Siemoneit Sabine , Kotila Sirpa , Heinz Dötz Karl , Nieger Martin 
Published: July 2007

AbstractTetracarbonyl‐π2‐alkyne–carbene chromium(0) complexes 3a–c stabilized by a rigid C2‐arene unit bridging the alkyne and the carbene ligands were synthesized from their pentacarbonyl precursors 2a–c by low‐temperature photodecarbonylation. The chelates 3a–c are the first stable alkyne–carbene complexes containing a Group VIB metal carbonyl unit, and can be regarded as arrested intermediates in the chromium‐mediated benzannulation reaction. Comparative X‐ray and 13C NMR studies indicate only weak coordination of the alkyne, both in the solid state and in solution. Decomposition of chelates 3a–c as well as the thermal decarbonylation of their pentacarbonyl precursors 2a–c results in dimerization of the alkynylcarbene ligands to give densely substituted oxygenated chrysene derivatives. A modification of the substitution pattern in the central chrysene rings results in a gradual distortion of the arene system across the central CC arene bond.
Crystalline Mono‐ and Multilayer Self‐Assemblies of Oligothiophenes at the Air–Water Interface
Authors: Isz Sandrine , Weissbuch Isabelle , Kjaer Kristian , Bouwman Wim G. , Als‐Nielsen Jens , Palacin Serge , Ruaudel‐Teixier Annie , Leiserowitz Leslie , Lahav Meir 
Published: July 2007

AbstractThe formation of Langmuir monolayers at the air–water interface has long been believed to be limited to amphiphilic molecules containing a hydrophobic chain and a hydrophilic headgroup. Here we report the formation of crystalline mono‐ and multilayer self‐assemblies of oligothiophenes, a class of aromatic nonamphiphilic molecules, self‐aggregated at the air–water interface. As model systems we have examined the deposition of quaterthiophene (S4), quin‐quethiophene (S5), and sexithiophene (S6) from chloroform solutions on the water surface. The structures of the films were determined by surface pressure–area isotherms, by scanning force microscopy (SFM) after transfer of the films onto atomically smooth mica, by cryo‐transmission electron microscopy (Cryo‐TEM) on vitreous ice, and by grazing incidence synchrotron X‐ray diffraction (GID) directly on the water surface. S4forms two polymorphic crystalline multilayers. In polymorph α, of structure very similar to that of the three‐dimensional solid, the molecules are aligned with their long molecular axis tilted by about 23° from the normal to the water surface. In polymorph β the long molecular axis is perpendicular to the water surface. S5self‐aggregates at the water surface to form mixtures of monolayers and bilayers of the β polymorph; S6forms primarily crystalline monolayers of both α and β forms. The crystalline assemblies preserve their integrity during transfer from the water surface onto solid supports. The relevance of the present results for the understanding of the early stages of crystal nucleation is presented.
Localization Patterns in Interstitial Space: A Special Property of the Electron Localization Function (ELF)
Authors: Nesper Reinhard , Wengert Steffen 
Published: July 2007

AbstractThe electron localization function (ELF) is a new descriptor of chemical bonding in real space which has turned out to be enormously powerful. We show here that the ELF also has predictive power. By analysis of the interstitial space, undetected atoms can be recognized by localization patterns in such regions. The importance of this approach is that the correct number of valence electrons is unknown before the calculations. The method was tested for the compounds Ca4Sb2O, Ba3Ge4X, Ba10Ge7O3, and for the so‐called second SrSi modification, which, according to our analysis, very probably has the composition Sr10Si10X. In these cases the positions of the heteroatoms O and X were located and, in the case of X, proposals for a preferred atom type or group are made. Even in cases where the missing atoms are the majority component the approach was quite successful. As an example, the structure of CaH2 was generated from the known Ca positions by a two‐step iterative procedure.
The Cation‐Dinitrogen Interaction in the “Benzyldiazonium ion”: Preferential Electrostatic Complex Formation and Dinitrogen Catalysis of Benzyl Cation Rotational Automerization
Authors: Glaser Rainer , Farmer David 
Published: July 2007

AbstractDiazonium ions are reactive intermediates in deamination reactions pertinent to chemical carcinogenesis. While methyldiazonium ion has been shown to exist as a short‐lived intermediate in the gas phase and in solution, benzyldiazonium ions have never been observed, and the reaction intermediates in deaminations of benzyl systems remain a matter of debate. We therefore studied the benzylcation‐dinitrogen interaction by ab initio methods; several important conclusions resulted. Analysis of the potential energy surface at the level MP4(sdtq)/6‐31 G*/ MP 2(full)/6‐31 G* + ΔVZPE(MP 2(full)/6‐31 G*) revealed that a classical “benzyldiazonium ion” does not exist. The interaction of N2with benzyl cationM‐1results in an electrostatically bound complex2Cwith a long CN distance (2.935 Å) as the most stable structure. A covalently bound planar benzyldiazonium ion2Awith a “normal” CN bond length (1.514 Å) is the transition‐state structure for automerization of the electrostatic complex with concomitant rotation about the exocyclic CC bond. The potential energy surface characteristics result from the highly efficient π‐dative Ph → CH2bonding inM‐1; this is clearly demonstrated in its structure and that of its transition state for rotational automerizationTS‐1by the very high activation barrier for rotation (47.6 kcalmol−1!) and by the gradient vector fields of the total electron densities of conformers of1and2. The rotational barrier for1is reduced to 27.9 kcalmol−1in the N2complex2, and the potential energy surface characteristics of benzyldiazonium ion essentially facilitate the N2‐catalyzed rotational isomerization of benzyl cation. The benzyldiazonium ion system shows for the first time that the interaction of a donor molecule with a carbenium ion with a valence LUMO can lead to the formation of an electrostatic complex as opposed to dative bond formation. Dative σ‐bond formation between N2and the CH2carbon of1is energetically not competitive with dative Ph → CH2π;‐bond formation.
Metal‐Template Electrophilic Substitution on Phenols: Synthesis and Crystal Structure of Bromomagnesium Phenolate and Its Reactive Complex with para‐Isopropylbenzaldehyde
Authors: Bocelli Gabriele , Cantoni Andrea , Sartori Giovanni , Maggi Raimondo , Bigi Franca 
Published: July 2007

AbstractThe crystal structures of the bromomagnesium phenolate 5 and its complex 7 with para‐isopropylbenzaldehyde are reported; for the first time it has been possible to demonstrate that the reactive complex 7, responsible for the complete ortho‐regioselective control in the alkylation of phenoxymagnesium bromides with aldehydes, is not obtained by simple replacement of the ethereal ligand but by expansion of the metal coordination sphere from 4 (usual tetrahedral configuration) to 5. We infer from 1H NMR studies that the magnesium coordination of complex 7 in solution is analogous to that shown in the solid state, with a complexed ethereal molecule.
Zirconium‐Mediated Intramolecular Coupling of Terminal Alkynes and Their Subsequent Carbonylation: Novel Synthesis of Seven‐ and Eight‐Membered Heterocycles
Authors: Barluenga José , Sanz Roberto , Fañanás Francisco J. 
Published: July 2007

AbstractThe development of a new method for the intramolecular coupling of terminal alkynes and for the synthesis of seven‐ and eight‐membered benzoheterocycles is reported. The key steps involve the generation of zirconocene‐alkyne complexes from 2‐bromoalkenes and the subsequent intramolecular carbometalation of olefins or acetylides. The 8‐unsubstituted zirconabicyclopentenes were carbonylated to afford unexpected products and allow access to polyfunctionalized molecules from simple starting materials.
The First Peralkylated Phosphino(stibino)methanes and Their Organometallic Rhodium Complexes
Authors: Manger Matthias , Wolf Justin , Laubender Matthias , Teichert Markus , Stalke Dietmar , Werner Helmut 
Published: July 2007

AbstractThe first representatives of phosphino(stibino)methanes R2PCH2Sb‐R′2 (3–5) with bulky alkyl or cycloalkyl groups R and R′ were prepared in two steps from Ph3SnCH2I via the isolated stannylated phosphanes Ph3SnCH2PR2 (1, 2) as intermediates. X‐ray structural analysis of 5 (R = C6H11, R′ = tBu) reveals that the lone pairs and the substituents R and R′ at phosphorus and antimony and the hydrogen atoms of the CH2 bridge adopt staggered conformations. Treatment of [{C8H12RhCl}2] with 3–5 affords the neutral compounds [Rh‐Cl(η4‐C8H12)(κ‐P‐R2PCH2SbR′2)] (6–8), of which 7 and 8 react with CH3MgI to give the corresponding methylrhodium derivatives [RhCH3(η4‐C8H12)(κ‐P‐R2‐PCH2SbR′2)] (9, 10). Cationic complexes [Rh(η4‐C8H12)(η2‐P,Sb‐R2PCH2SbR′2)]‐X (X = PF6: 11a, 12a, 13; X = BPh4: 11b, 12b) containing the phosphino(stibino)methanes as chelating ligands were obtained either from [{C8H12RhCl}2], R2PCH2SbR′2 and MX, or (for 13) from 8 and AgPF6. Compound 12a (R = iPr, R′ = tBu) was characterized by X‐ray crystallography. The PF6 salts 11a, 12a, and 13 react with CH2N2 by insertion of CH2 into the Rh–Sb bond to yield the complexes 14–16, the first examples of transition‐metal compounds with Sb ylides as ligands. Treatment of BPh4 salts 11b and 12b with H2 gives the half‐sand‐wich‐type complexes [(η6‐C6H5BPh3)Rh(κ2‐P,Sb‐R2PCH2SbR′2)] (17, 18), in which the tetraphenylborate is coordinated like a substituted arene to the metal center.
Chiral Lewis Acid Controlled Synthesis (CLAC Synthesis): Chiral Lewis Acids Influence the Reaction Course in Asymmetric Aldol Reactions for the Synthesis of Enantiomeric Dihydroxythioester Derivatives in the Presence of Chiral Diamines Derived from L‐Proline
Authors: Kobayashi Shū , Horibe Mineko 
Published: July 2007

AbstractBoth enantiomers of 2,3‐dihy‐droxythioester derivatives were prepared with almost perfect stereochemical control by chiral Lewis acid controlled synthesis (CLAC synthesis). CLAC synthesis means synthesis of all individual diastereomers or enantiomers from the same starting materials by designing chiral Lewis acids. For example, (Z)‐1‐ethyl‐thio‐1‐(trimethylsiloxy)‐2‐(tert‐butyldi‐methylsiloxy)ethene (1) reacted with aldehydes in the presence of chiral tin(II) Lewis acids using (S)‐1‐methyl‐2‐[(isoin‐dolinyl)methyl]pyrrolidine (4) and (S)‐1‐methyl‐2‐[(indolinyl)methyl]pyrrolidine (5) to afford enantiomeric dihydroxy‐thioester derivatives. Chiral diamines 4 and 5, which were readily prepared from L‐proline, differ only in the fusion point of the benzene ring connected to the pyrrolidine moiety. The unique selectivities were ascribed to the conformational difference between the chiral tin(II) Lewis acids of chiral diamines 4 and 5, and the function of chiral sources for obtaining high selectivities has also been clarified.