bluuebunny/crossref_metadata_2025 huggingface dataset:
Interpretation of 31P‐NMR Coordination Shifts for Phosphane Ligands. Ab Initio ECP/DFT Study of Chemical Shift Tensors in M(CO)5L [M = Cr, Mo, W; L = PH3, P(CH3)3, PF3, PCl3]
Authors: Kaupp Martin
Published: July 2007

The 31P chemical shift tensors of the transition‐metal phosphane complexes M(CO)5PX3 (M = Cr, Mo, W; X = H, CH3, F, Cl) were studied using a combination of density functional theory and ab initio effective‐core potentials. The calculated isotropic shifts agree well with experimental results both for the free ligands and for the complexes, with the largest deviations occuring for the tungsten complexes. A breakdown of the computed phosphorus shielding tensors into contributions from localized molecular orbitals (LMOs) indicates that the positive coordination shift of PH3 and P(CH3)3 is due to increased paramagnetic contributions from the phosphorus lone pair (P‐M s̀ bonding) LMO to δ⊥. A similar increase of this contribution is found for PF3 and PCl3. However, for PCl3 complexes these terms are overcompensated by a reduction in the paramagnetic contributions from the P‐Cl bonds and by shielding contributions from metal‐centered orbitals. This results in a negative overall coordiantion shift. A partial cancellation is found with P(CH3)3 and with PF3. The changes in the 31P‐shift tensors of the same phosphane ligands upon protonation are qualitatively and quantitatively very different from the coordination shifts and do not provide good models for the latter.
Metal‐Catalyzed Oxidations, 4. The Reaction of Molybdenumperoxo Complexes with Brønsted and Lewis Acids
Authors: Thiel Werner R.
Published: July 2007

NMR studies of the reaction of complexes of the type (L‐L)MoO(O2)2 (L – L= bidentate ligand) with strong Brønsted and Lewis acids prove that protons are transferred preferentially to an η2‐peroxo and not to the oxo ligand. This behavior in proton transfer reactions is one critical point of the catalytic activity of such complexes in olefin epoxidation. EH calculations on the model complex (NH3)2MoO(O2)2 support the spectroscopic investigations.
Conformation of tripod Metal Templates in CH3C(CH2PPh2)3MLn (n = 2, 3): Neural Networks in Conformational Analysis
Authors: Beyreuther Stefan , Hunger Johannes , Huttner Gottfried , Mann Susanne , Zsolnai Laszlo
Published: July 2007

The conformational space spanned by tripod metal templates CH3C(CH2Ph2)3M is analysed on the basis of the solid‐state structures of 82 tripodCo templates in compounds tripodCoL2 and tripodCoL3. Systematic analysis, including the techniques of conformational space group scatter graphs, principal‐component analysis, and partial least squares, reveals a series of basic regularities: The torsion of the phenyl groups is strongly linked to the torsional skew of the bicyclooctane‐type framework of the chelate cage. For one sense of this skew there are two classes of low‐energy conformation that differ by the helicity of the phenyl arrangement and by the degree of torsional skew in the chelate backbone. From the scatter graphs it is evident that a change in helicity may occur by one‐ or by two‐ring flip mechanisms. The basic regularities found by the above methods are also evident from the analysis of the same data by a neural network approach. The fact that these regularities are found for tripodCoL2 and tripodCoL3, irrespective of the widely different coligands L and crystal environments, means that the conformation of the tripod metal templates is governed by the forces acting within them and not so much by the forces imposed on them by their individual chemical or crystal environment. It is shown that the classifications, although derived from a data basis only containing Co compounds, are characteristic for tripod metal templates irrespective of the specific metal involved.
The First SiH Complex, Dihydridotetrakis(3‐picoline)silicon Dichloride–Tetrakis(chloroform), [H2Si(3pic)4]Cl2 · 4 CHCl3: Formation, Chemical Equilibria, and Structural Investigation by NMR Spectroscopy and Single‐Crystal X‐ray Diffraction
Authors: Fleischer Holger , Hensen Karl , Stumpf Thorsten
Published: July 2007

Bis(dichlorosilyl)amine reacts in chloroform solution with 2‐picoline to give H3SiCl, H2SiCl2, and HSiCl3, whereas with 3‐picoline the two hypervalent silicon compounds H2SiCl2‐(3pic)2 and [H2Si(3pic)4]Cl2 · 4 CHCl3 containing hexacoordinated Si atoms are formed. These complexes are in a chemical equilibrium with each other in chloroform solution, from which crystals of [H2Si(3pic)4]Cl2 · 4 CHCl3 could be isolated. The crystal structure of the latter was determined by single‐crystal X‐ray diffraction. The complex can be regarded as an “contact ion trio” of [H2Si(3pic)4]2+ and two Cl– ions. The N–Si bond lengths, r(Si–N) = 196.9(3) and 197.5(3) pm, are similar to those found in neutral hexacoordinated Si complexes. The data obtained from a 1H1H ROESY experiment suggest that dissolution has no significant impact on the molecular structure of [H2Si(3pic)4]Cl2 · 4 CHCl3.
New Bis(lithiomethyl)silanes: Building Blocks for Organosilanes
Authors: Strohmann Carsten , Lüdtke Silke , Wack Eric
Published: July 2007

The first high yield preparation of non π‐stabilized bis(lithio‐methyl)silanes was performed by the reductive cleavage of C–S bonds with electron transfer reagents. Bis[(phenylthio)‐methyl]silanes synthesized by the reaction of dichlorosilanes with [(phenylthio)methyl]lithium were transformed to the corresponding bis(lithiomethyl)silanes 7 by reaction with lithium naphthalenide (LiC10H8) or lithium p,p′‐di‐tert‐butyl‐biphenylide (LiDBB) as an electron transfer reagent and were characterized by their reaction with Bu3SnCl. The C–S bonds of bis[(phenylthio)methyl]silanes can be cleaved selectively making possible the introduction of two different groups. – The silicon atom plays a central role in the reactivity of the presented structural types. The bis(lithiomethyl)silanes are used as new building blocks for the preparation of organosilanes, Si–H‐functionalized organosilanes, and 1,3‐disilacyclobutanes containing SiCH2Si structural units.
Organoamido‐ and Aryloxo‐lanthanoids, 14. Organometallic Compounds of the Lanthanoids, 106. Synthesis and Characterisation of Complexes of Lanthanoid Pyrazolates with 1,2‐Dimethoxyethane and the X‐Ray Structures of (1,2‐Dimethoxyethane‐O1:O2)(1,2‐dimethoxyethane‐O1)tris(3,5‐diphenylpyrazolato)erbium(III) and catena‐Poly[tris(3,5‐di‐tert‐butylpyrazolato)‐μ‐(1,2‐dimethoxyethane‐O1:O2)‐neodymium(III)]
Authors: Cosgriff Joanna E. , Deacon Glen B. , Fallon Gary D. , Gatehouse Bryan M. , Schumann Herbert , Weimann Roman
Published: July 2007

The complexes [Ln(Ph2pz)3 (DME)2] and [Ln(tBu2pz)3 (DME)] (Ln = La, Nd, Er; Ph2pzH = 3,5‐diphenylpyrazole; tBu2pzH = 3,5‐di‐tert‐butylpyrazole; DME = 1,2‐dimethoxyethane) have been prepared by reaction of the lanthanoid metal with bis(pentafluorophenyl)mercury and the pyrazole in DME. The molecular structures of [Er(Ph2pz)3 (DME)2] (3) and [Nd(tBu2pz)3 (DME)]∞ (5) have been determined by X‐ray diffraction. Complex 3 has nine‐coordinate Er with three chelating Ph2pz ligands and one chelating and one η1‐bound DME. There is a trigonal prismatic arrangement of the oxygen donors and the centres of the N – N bonds. 5 was found to be a linear polymer with transoid DME ligands bridging Nd(tBu2pz)3 units in a novel manner. The centres of the N – N bonds (which are essentially coplanar with Nd), and the oxygen donor atoms adopt an arrangement intermediate between trigonal‐bipyramidal and square‐pyramidal [O – Nd – O 153.5(2)°].
Copper Coordination Polymers with Infinite Chloride Ion Channels and Different Directions of the Jahn‐Teller Distortion, Built from Tris(1,2,4‐triazolyl)borate as a Modified Tris(pyrazolyl)borate Ligand
Authors: Janiak Christoph , Scharmann Tobias G. , Günther Wulf , Hinrichs Winfried , Lentz Dieter
Published: July 2007

[Co{HB(C2H2N3)3}2] reacts with an excess of CuCl2 in hot water with formation of ∞2[Cu2Cl2{μ3‐HB(C2H2N3)3}2 · 2 H2O] (7) or ∞3{[Cu2{μ4‐HB(C2H2N3)3} (μ‐OH)2]Cl · 6 H2O} (8), depending on the reaction time. 8 can also be obtained from [Cu{HB(C2H2N3)3}2] and CuCl2 in aqueous ammonia. The 2‐D double‐layer‐type coordination polymer 7 crystallizes in the orthorhombic space group P212121. The two different Cu(II) centers in the lattice are distinguished only be the direction of the Jahn‐Teller distortion. The following corresponding distances for the CuClN5 coordination sphere were found Cu1/Cu2–Cl = 2.572(2)/2.328(2), Cu1/Cu2–N = 2.585(5)/2.077(4); 2.000(4)/1.979(5); 2.100(5)/2.734(5); 2.005(4)/1.994(4); 2.024(5)/2.369(5). In the 3‐D coordination polymer 8 one of the two different Cu centers is chelated by the three endodentate nitrogen donors, while the other Cu center is coordinated by three exodentate nitrogen atoms. The coordination sphere is completed in both cases by two hydroxo bridges to symmetry‐related Cu centers. The metal‐ligand connectivity creates infinite channels with helical walls which contain the solvated chloride anions.
Synthesis and Structure of Mononuclear Titanium Complexes Containing ansa‐Aminopyridinato Ligands
Authors: Oberthür Markus , Arndt Perdita , Kempe Rhett
Published: July 2007

A series of siloxane‐bridged bis(2‐aminopyridines) were synthesized from dichlorosiloxanes and 2‐aminopyridines in the presence of a base via nucleophilic substitution reactions. They were used, after deprotonation, as dianionic (ansa‐aminopyridinato) ligands to stabilize mononuclear titanium complexes with unusual coordination geometries. An X‐ray crystal structure analysis of one of the ligands and of a titanium complex proved mononuclearity and provided information about the binding mode of this novel type of ligands. Ethylene polymerization studies showed low activity, remarkable differences between structurally related complexes, and broad molecular weight distributions. Sterically less demanding substituents and a high basicity of the ligand increase polymerization activity.
Diboran(4)yl Groups as Ligands to Transition Metals
Authors: Braunschweig Holger , Ganter Beate , Koster Margot , Wagner Trixie
Published: July 2007

Reaction of Na[(Cp)Fe(CO)2] and Na[(Cp)W(CO)3] with B2(NMe2)2Cl2 yields the first transition metal‐substituted diboranes [Cl(Me2N)B–B(NMe2)M(Cp)(CO)n] [M(Cp)(CO)n  Fe(Cp)(CO)2, W(Cp)(CO)3] (1a, b). The compounds were characterized in solution by NMR methods and in the crystal by X‐ray structural determination.
Reaktionen des Tripod‐Co‐Templats CH3C(CH2PPh2)3Co(II) mit funktionalisierten Hydrazinen
Authors: Körner Volkmar , Vogel Sabine , Huttner Gottfried , Zsolnai Laszlo , Walter Olaf
Published: July 2007

The coordination behaviour of ligands having the same basic constitution RN=NC(=X)R′ (X  O, NR″, S) in their tripod cobalt derivatives has been analyzed. The ligands themselves may be considered as neutral heterodiene compounds and are in this respect vinylogues to diazenes RNNRy′. Two‐ electron reduction of these neutral species results in dianionic heterosubstituted heteroolefins RN‐ ‐NC(X‐)R′. Due to their redox ambiguity the oxidation state of the metal M in chelate complexes is not a priori evident. Compounds tripod [5: X, R′  O, Ph; 6; (X, R′)  (py); 7: X, R′  S, NH2] are best described as containing low‐spin Co(III) and dianionic ligands. Co(II) species are obtained with diethyl azodicarboxylate EtOOCNNCOOEt as the ligand. In the mononuclear compound, with only one nitrogen and one carbonyl oxygen of the ligand acting as donor groups, the neutral ligand is coordinated to give the high‐spin cobalt(II) species tripod (8). In the dinuclear compound 9 with both of the nitrogen atoms and carbonyl groups involved in coordination the dianionic ligand bridges two high‐spin cobalt(II) centers to give tripod (9) as a derivative with two fused five‐membered chelate rings. In addition to the conventional analytical techniques X‐ray structure analyses, cyclovoltametric measurements, magnetic susceptibility and ESR data are used to characterize the compounds.
Crystal Structures and Preparation of K2AgVS4 and Rb2AgVS4 by Using the Molten Flux Method: Low‐Dimensional Materials with Infinite Metal‐Ion‐Centered Tetrahedra Chains
Authors: Bensch Wolfgang , Dürichen Peter
Published: July 2007

The quaternary sulfides K2AgVS4 and Rb2AgVS4 crystallize as dark violet needle‐like crystals with a metallic lustre. Infinite Ag‐ and V‐centered tetrahedra sharing common edges are running parallel to the crystallographic a axis. The chains are separated by K+ or Rb+ ions which are in an eightfold environment. The tetrahedra are occupied in an ordered fashion. The Ag–V interatomic distances amount to 2.904(1) and 2.910(1) A, respectively, which is significantly larger than the sum of the ionic radii of Ag+ and V5+. Whereas the V–S distances are in the normal range, the average (Ag–S) distances are the shortest reported so far indicating strong covalent bonding between monovalent Ag+ and S2–. In addition, the title compounds represent very rare examples of AgS4 polyhedra with equidistant Ag–S bonds. The geometrical parameters within the tetrahedra chains are only slightly affected when K+ is replaced by the larger Rb+ demonstrating the rigidity of the bonding properties within the tetrahedra. The compounds are isotypic with the quaternary copper sulfide K2CuVS4 and the selenides K2CuMSe4 (M=Nb, Ta).
A Palladium‐Catalyzed Domino Coupling Process Leading to Annelated Pentafulvenes
Authors: Dyker Gerald , Nerenz F. , Siemsen P. , Bubenitschek P. , Jones Peter G.
Published: July 2007

Annelated pentafulvenes 2, 10, 13, and 14 are efficiently accessible by a palladium‐catalyzed domino coupling process of aryl substituted vinylic bromides 1, 9, 11, and 12, 5‐Membered palladacycles 3 are discussed as key intermediates.
Organmetallic Selenolates, IV. Reactions of MSeW(CO)3cp (M=Li, Na) with Organodi‐ and ‐tetrahalides – X‐ray Crystal Structures of C6H5CH2W(CO)3(η5‐C5H 5), μ‐[m‐C6H4{CH2SeW(CO)3(η5‐C5H5)}2], μ‐[p‐C6H4{CH2SeW(CO)3‐ (η5‐C5H5)}2], and C6H5CH[SeW(CO)3(η5‐C5H5)]2
Authors: Eikens Wolfgang , Jäger Stefan , Jones Peter G. , Laube Jörg , Th öne Carsten
Published: July 2007

Organotungsten‐selenolato complexes were prepared in moderate yields by insertion of selenium into the alkali metaltungsten bonds of MSeW(CO)3cp (M = Li, Na) and subsequent reactions with the organohalides o‐, m‐, and p‐ C6H4(CH2Br)2, C6H5CHBr2, m‐C6H4(CHBr2)2 and C6H5CCl3. The 77Se‐NMR data of the new complexes are discussed and compared with those of related complexes derived from organomonohalides. Moreover, the X‐ray crystal structures of C6H5CH2W(CO)3cp (1), μ‐[m‐C6H4{CH2SeW(CO)3cp}2] (3), μ‐[p‐C6H4{CH2SeW(CO)3cp}2] (4), and C6H5CH[SeW‐(CO)3cp]2 (5) were determined. In complex (1), the W–CH2 bond length is 2.374 Å; the W–Se bond lengths in the complexes 3, 4 and 5 are all in the range 2.625–2.655 Å, corresponding to W–Se single bonds.
Reactions of Lactams with Titanocene‐ and Zirconocene‐Alkyne Complexes as Elemental Steps in Catalytic Anionic Ring‐Opening Polymerization of Lactams
Authors: Arndt Perdita , Lefeber Claudia , Kempe Rhett , Tillack Annegret , Rosenthal Uwe
Published: July 2007

Depending on the nature of the metal and the ring size, lactams react with titanocene and zircocene complexes of bis‐(trimethylsilyl)acetylene Cp2Ti(Me3SiC2SiMe3) and Cp2Zr‐(L)(Me3SiC2SiMe3) (L = Py, THF) to yield different products. In the reaction of Cp2Zr(Py)(Me3SiC2SiMe3) with N‐methyl‐€‐caprolactam a simple ligand exchange reaction occurs and the complex Cp2Zr(Me3SiC2SiMe3)[OH2)5] (1) was isolated. With β‐propiolactam the alkenyl‐amido complex Cp2)(SiMe3)][–NH2] (2) was obtained, which indicates that an agostic metal‐hydrogen interaction has taken place. The reaction of Cp2Ti(Me3‐SiC2SiMe3) with €‐caprolactam gives after elimination of the alkyne and molecular hydrogen the first early transition metal complex with a deprotonated coordinated €‐caprolactam in a η2‐amidate bonding fashion (3). The obtained complexes were characterized by NMR spectra (1, 2) and crystal structure analysis (1–3) and discussed as elemental steps in anionic ring‐opening polymerization of lactams catalyzed by metallocene‐alkyne complexes.
Suzuki‐Coupling of Cp*Ru(para‐C6H4Br2) with Phenyl Boronic Acid: A Model Reaction for the Synthesis of Organometallic Polymers
Authors: Harre Kathrin , Enkelmann Volker , Schulze Margit , Bunz Uwe H. F.
Published: July 2007

The synthesis of a terphenyl derivative complexed by the cationic moiety Cp*Ru+ by Suzuki coupling of [Cp*Ru(BrC6H4Br)]OTf with phenyl boronic acid under catalysis of Pd(PPh3)4 in a DME‐water mixture at 85°C in quantitative yield is reported. The stable coupling product 3 was characterized by X‐ray crystal structure analysis.
A Theoretical Study of Thionitrosyl Azide (N3NS), Thiazyl Azide (N3SN) and Nitrosyl Azide (N3NO)
Authors: Nguyen Minh Tho , Flammang Robert
Published: July 2007

Stimulated by the recent detection of nitrosyl azide (N3NO), we investigated the stability of the sulfur analogues thionitriosyl azide (N3NS) and thiazyl azide (N3SN) by using ab initio MO calculations up to the QCISD(T)/6‐311+G(d)//QCISD/6‐311G(d) + ZPE level. Both azides have a similar energy content. While thionitrosyl azide is not stable with respect to N2 elimination, thiazyl azide resists to this process by an energy barrier of about 110 kJ/mol. The NS and N3 fragments resulting from homolytic cleavage lie about 100 kJ/mol above the azides. The five‐membered ring is thermodynamically much more stable than both azides but kinetically unstable with respect to cheletropic decomposition yielding N2S + N2. Overall, trans‐thiazyl azide is the most likely candidate for experimental observation of, for example, the reaction of NS+ salts with the azide anion. IR wavenumbers of the azides were also predicted.
Preparation and Reactivity of Tris(trifluoromethylselanyl)carbenium [(CF3Se)3C+] and Trifluoromethylsulfanylacetic Acid Derivatives [(CF3S)3–nCXn(O)R]
Authors: Haas Alois , Möller Guido
Published: July 2007

Reaction pathways for the synthesis of the (CF3E)3C moieties (E = Se, S) are described. [(CF3Se)3C+][AsF] was found to be a suitable synthon for the preparation of (CF3Se)3C derivatives. It can be prepared either from (CF3Se)3C derivatives. It can be prepared either from (CF3Se)4C or (CF3Se)3CF and AsF5 in liquid SO2. Direct access to (CF3Se)3CF was realized by the reaction of FCBr3 with Hg(SeCF3)2. Treatment of [(CF3Se)3C+][AsF6‐] with potassium halides provided (CF3Se)3CX (X = F, Cl, Br). A different course took the reaction with KI, as CF3SeSeCF3 and (CF3Se)2C=C(SeCF3)2 were formed as main products. Minor amounts of (CF3Se)3CC(SeCF3)3 were formed which could be isolated and unambiguously characterized. Only two routes led to a threefold CF3S‐substituted acetic acid ester (CF3S)3CC(O)OR [R = CH3, (CH3)3C]: Metatheses between (CF3S)2CBrC(O)OCH3 and Hg(SCF3)2 and metalation of (CF3S)2CHC(O)OR [R = CH3, (CH3)3C] with NaH followed by reaction with CF3SCl. Other precursors such as (CF3S)2CXC(O)OR′ [X = H, Br; R′ = Me3Si, (n‐C4H9)3Sn] and (CF3S)2CBrC(O) Y (Y = Cl, Br) were synthesized but could not be converted to the corresponding (CF3S)3C derivatives. Attempts to hydrolyze (CF3S)3CC(O)OR to (CF3S)3CC(O)OH failed.
Preparation and X‐ray Crystal Structure of the First Trimeric Nickel Thiosemicarbazone Complex: The First Example of Oligomerization by both NiONi and NiSNi Bridging
Authors: Berkessel Albrecht , Hermann Gesine , Rauch Olga‐Tatjana , Büchner Michael , Jacobi Albrecht , Huttner Gottfried
Published: July 2007

Monomeric nickel(II) thiosemicarbazone complexes are an attractive new class of homogeneous catalysts for the activation of silanes. However, their activity is limited by the formation of inactive oligo‐ and polymers. The pathway by which aggregation takes place was elucidated by the preparation and X‐ray structural analysis of the first trimeric nickel(II) thiosemicarbazone complex. Aggregation was shown to proceed via NiONi and NiSNi bridging, giving rise to both fourfold planar and pseudooctahedral coordination of the nickel ions.
Synthesis and Substituent Interactions of Tricarbonylchromium‐complexed Arylalkynylbenzenes — Novel Organometallic Push‐pull Chromophores
Authors: Müller Thomas J. J. , Ansorge Markus , Lindner Hans Jörg
Published: July 2007

The tricarbonylchromium complexes chlorobenzene 1 reacts with terminal alkynes 2 through a palladium‐copper‐catalyzed coupling to give a variety of Cr(CO)3‐complexed phenylethynyl arenes, heteroarenes and ferrocene 3 in good to excellent yield. Due to the electron‐withdrawing nature of the Cr(CO)3 group these novel complexes can be regarded as organometallic push‐pull chromophores. Analogously, the corresponding free ligands 4 (phenylethynyl arenes, heteroarenes and ferrocene) were synthesized by coupling iodobenzene and 2. The crystal structure analysis of the singly Cr(CO)3‐complexed tolane 3e reveals a strong deviation from coplanarity of both phenyl rings by an angle of 50.9(2)° presumably due to crystal packing. Correlations are established between selected substituent parameters (σP, σI, σR, σP+ and Δπ) and the carbonyl carbon resonances in the 13C‐NMR spectra for the complexes 3. The overall electronic substituent effect is transmitted to the carbonyl groups by both mesomeric and inductive mechanisms. The push‐pull complexes 3 display relatively small negative solvochromicities of longest wavelength absorption band (MLCT band).
Synthesis and Stereochemistry of the First Chiral (Imidazolinylidene)‐ and (Triazolinylidene)palladium(ii) Complexes
Authors: Enders Dieter , Gielen Heike , Raabe Gerhard , Runsink Jan , Teles J. Henrique
Published: July 2007

The reaction of three equiv. of a chiral imidazolium or triazolium perchlorate with one equiv. of Pd(OAc)2, an excess of NaI and a base leads to the corresponding chiral dicarbenediiodopalladium(II) complexes in chemical yields up to 98% and with the trans isomer as the major product (1, 2). If only one equiv. of the imidazolium or triazolium perchlorate is used, then dinuclear complexes with bridging iodine atoms are formed (3, 4, chemical yield 92—94%). The latter can add Lewis basic ligands, e.g. amines, phosphanes or other carbenes, to give mononuclear complexes with one carbene ligand coordinated to the PdI2 fragment (5, 6). Preliminary test experiments with these Pd(II) complexes as catalysts for an enantioselective Heck‐type reaction have been carried out.
The Interlocking of Salicylic Aldehydes and Ketones with a 2h‐1,2,4,3‐Triazaphosphole
Authors: Schmidpeter Alfred , Steinmüller Franz , Nöth Heinrich
Published: July 2007

Salicylic aldehyde (2a) adds to 2‐methyl‐5‐phenyl‐2H‐1,2,4,3‐triazaphosphole (1) to yield the bicyclic phosphonic amide 3a. The OH group adds to the P=N bond, the carbon atom the carbonyl group is inserted into the other P—N bond, and the phosphorus atom is oxidized. In the crystal the compound forms dimers by a double hydrogen bond between two HN‐PO units. Substituted salicylic aldehydes as well as ortho‐hydroxyacetophenone and benzophenone react in the same way.
Phosphazenes with (2‐Pyridylmethylamino) Groups, I. Syntheses and Crystal Structures of Pentaphenoxy(2‐pyridylmethylamino)‐cyclotriphosphazene and Its Copper(II) Nitrate, Platinum (II) Chloride, and Cobalt(II) Nitrate Complexes
Authors: Diefenbach Ursula , Kretschmann Michael , Stromburg Brigitte
Published: July 2007

The reaction of the (2‐pyridylmethylamino)‐substituted cyclotriphosphazene N3P3(OC6H5)5(NHCH2(C5H4N)‐2) (1) with copper(II) nitrate, platinum(II) chloride, and cobalt(II) nitrate yields the stable complexes [Cu(NO3)2·(1)2] (1a), [PtCl2·(1)] (1b), [Co(NO3)2 · (1)] (1c). The X‐ray crystallographic studies of these metal complexes revealed the different coordination behavior of the multifunctional ligand.
Halogen/Metal vs. Hydrogen/Metal Exchange: General or Specific Site Selectivity as Exemplified in the Camphene Series
Authors: Garamszegi László , Schlosser Manfred
Published: July 2007

(Z)‐(3,3‐Dimethylbicyclo[2.2.1]hept‐2‐ylidene)methyllithium can be readily generated by treatment of (Z)‐3‐bromomethylene‐2,2‐dimethylbicyclo[2.2.1]heptane with tert‐butyl‐lithium. At ‐75°C, the organometallic intermediate is configurationally stable and reacts with a variety of electrophiles under stereochemical retention.
Synthesis and Structure of Binuclear Single‐Bridged Bis[(phosphane)gold(I)]halogenonium Complexes
Authors: Bayler Angela , Bauer Andreas , Schmidbaur Hubert
Published: July 2007

Reactions of (R3P)AuX (X = Cl, Br, I) with [(R3P)Au]+ BF−4 obtained from (R3P)AuCl and AgBF4 in tetrahydrofuran, lead to cationic binuclear gold(I) complexes of the general formula ([(R3P)Au]2X}+ BF−4. A number of chloro‐ (R = Ph, o‐Tol, Mes, Bzl, Et), bromo‐ (R = Ph, o‐Tol, Mes) and iodo‐bridged (R = Ph, Mes) complexes of this type have been isolated and identified on the basis of their analytical and spectroscopic data. The crystal structure of bis[(triphenylphosphane)gold(I)]bromonium tetrafluoroborate was determined by single‐crystal X‐ray diffraction. The cations contain two‐coordinate bromine atoms with an Au‐Br‐Au angle of 96.83(3)°.
Chemie polyfunktioneller Moleküle, 125 Synthese und Kristallstruktur von N,N,N′,N”︁,N‐Pentamethyl‐diethylentriamin‐cokoordiniertem Kalium‐bis(diphenylphosphanyl)amid
Authors: Ellermann Jochen , Schütz Martin , Heinemann Frank W. , Moll Matthias , Bauer Walter
Published: July 2007

The metalation of bis(diphenylphosphanyl)amine [HN‐(PPh2)2,1 with KOtBu at 95°C in toluene affords a pale yellow precipitate of potassium bis(diphenylphosphanyl)amide (3a). On addition of liquid N,N,N′,N”︁,N”︁‐pentamethyldiethylenetriamine (PMDTA, 4) the precipitate dissolves in toluene at 115°C to give a yellow solution, from which yellow‐green blocks of [(Ph2P)2NK·PMDTA] (3b) are obtained. X‐ray analysis reveals that the coordination sphere of potassium consists of the chelating triamine ligand and [N(PPh2)2]− as N‐donor as well as η1 and η2 C‐donor with two phenyl fragments. No phosphorus coordination of [N(PPh2)2]− is observed.
Cobalt‐Catalyzed Selective Oxidation of the Tritertiary Phosphane Triphos with Molecular Oxygen
Authors: Heinze Katja , Huttner Gottfried , Zsolnai Laszlo
Published: July 2007

The reactivity of complexes of triphos [CH3C(CH2PPh2)3] and CoCl2 towards dioxygen has been investigated. Reaction of the pseudo‐tetrahedral complex (η2‐triphos)CoCl2 (1) with dioxygen yields after work‐up the mixed phosphane/phosphane oxide ligands triphosO and triphosO2. The novel ligand triphosO2 can be obtained in quantitative yield using catalytic amounts of 1. In order to gain some insight into the catalytic dioxygen activation reaction, experiments with various triphos/Co/Cl species, in different solvents and at several concentrations have been carried out. A mechanism involving two separate reaction pathways is proposed. Complexes of triphosO and triphosO2 with CoCl2, [η2‐(P, P)‐triphosO]CoCl2 (4), and [η2‐(P, O)‐triphosO2]CoCl2 (5), which are present as intermediates in the oxygenation reaction, have been isolated and fully characterized including X‐ray structural analyses.
Cyclic and Bicyclic Poly(phosphane)borane Cations
Authors: Sigl Mareus , Sehier Annette , Schmidbaur Hubert
Published: July 2007

The reactions of (Me2S)BH2Br and (Me2S)BHBr2 with equimolar quantities of 1,2‐bis(diphenylphosphanyl)ethene (1) or ‐benzene (2) lead to cyclic, cationic bis(phosphane)boranes [4[(1)BH2]+ Br−; 6: [(2)BH2]+ Br; 7: [(2)BHBr]+ Br−]. The Br counterions can be exchanged in metathesis reactions (e.g. with AgBF4 to afford 4a). The tritertiary phosphane bis[2‐(diphenylphosphanyl)phenyl]phenyl‐phosphane (3), reacts with (Me2S)BHBr2 to give bicyclic dicationic tris(phosphane)borane 8, [(3)BH]2+ Br−, which can be converted into the bis(hexafluorophosphate) 8a using NH4PF6. All compounds have been characterized by analytical and NMR‐spectroscopic data. The crystal and molecular structures of 5 ‐ 7 have been determined by single‐crystal X‐ray diffraction. The five‐membered rings C2P2B have an envelope conformation and show no sign of electron delocalization. Attempts to deprotonate the BH functions in 5 – 8 have not been successful. Clearly, the two (5 – 7) or three phosphonium centers (8) adjacent to the boron atom are not sufficient to induce an “umpolung” of the BH group
Structure and Reactivity of Sodium Phenoxide ‐ Following the Course of the Kolbe‐Schmitt Reaction
Authors: Kunert Michael , Dinjus Eckhard , Nauck Maria , Sieler Joachim
Published: July 2007

Solvent‐free sodium phenoxide (NaOPh) crystallises as a polymer and forms a polymeric chain in the [0 0 1] direction. The low coordination of the sodium atoms, as evident in the crystal structure, is confirmed by the easy coordination of oxoligands (α‐donors). Hence, the four‐membered ring chain of the solvent‐free sodium phenoxide is separated by oxoligands, and forms partial structures as the polymer fragments. Thus, NaOPh crystallises in THF with the formation of an Na6O6 core, consisting of two face‐fused heterocubes, and in N, N, N′, N′‐tetramethyl urea (TMU) with the formation of a Na4O4 heterocubane. The solvent‐free NaOPh‐CO2 complex obtained from the addition of CO2 to a solution of sodium phenoxide is, when exposed to a temperature of 80°C, subject to an irreversible phase transition, as demonstrated by FT‐IR and DTA studies. The complex formed at 80°C is, apparently, another intermediate of the Kolbe‐Schmitt reaction.
P/O Ligand Systems: Facile Synthesis, Structure, and Catalytic Tests of 2′‐Phosphanyl‐1,1′ ‐phenyl‐2‐ols and 2′‐Phosphanyl‐1,1′‐binaphthyl‐2‐ols
Authors: Kadyrov Renat , Heinicke Joachim , Kindermann Markus K. , Heller Detlef , Fischer Christine , Selke Rüdiger , Fischer Axel K. , Jones Peter G.
Published: July 2007

A facile synthesis of 2′‐phosphanyl‐1,1′‐biphenyl‐ and 2′‐phosphanyl‐1,1′ ‐binaphthyl‐2‐ols and their silyl ethers has been developed, consisting of electron‐transfer‐catalyzed ring‐opening of dibenzofuran and dinaphthofuran, respectively, subsequent reaction with chlorophosphanes, and work‐up with acetic acid or ClSiMe3. Studies of the molecular and crystal structures reveals the presence of P—H—O bridging bonds in the more basic tBuPhP derivative and a nearly perpendicular arrangement of the aryl planes in the biphenyl derivatives. The barrier to rotation of the aryl planes about the C–C axis was determined by NMR in the case of the P‐asymmetric derivative 3d, using the appearence of diastereoisomers by atropisomerism and P‐asymmetry. Comparative screening tests of the title compounds, phosphanyl phenols and phosphanylnaphthols in homogeneous Rh‐catalyzed reactions demonstrate catalytic activity in hydroformylation reactions and superior properties of the biphenyl‐ and binaphthyl‐2‐ol derivatives in relation to other P–O ligands.
Coordination Chemistry of Pentahalocyclopentadienyls
Authors: Sünkel Karlheinz
Published: July 2007

The coordination chemistry of perhalocyclopentadienyl ligands, first developed in the early 1970's as a part of a research program directed towards the synthesis of oxidation‐resistant fuel additives, has been revived in the last ten years. This renewed interest stems from the discovery that the coordinated cyclopentadienyl ligand allows multiple functionalizations. Thus, the high versatility of this important class of ligands can be broadened even further, which may be important with regard to industrial applications of metallocenes.
Compounds of Germanium and Tin, 22 – Reactions of a Silyene with a Germylene and a Stannylene: Formation of a Digermene with an Unusual Arrangement of the Substituents and of a Stannane
Authors: Schäfer Annemarie , Saak Wolfgang , Weidenbruch Manfred , Marsmann Heinrich , Henkel Gerald
Published: July 2007

The reaction of the diaminosilylene :Si(tBuNCH2CH2NtBu) (5) with the diaminogermylene :Ge(tBuNCH2CH2NtBu) is thought to proceed via a germasilene → silylgermylene rearrangement and dimerisation to furnish the (Z)−1,2‐diamino‐1,2‐disilyldigermene (Z)‐9. The X‐ray structure analysis of (Z)‐9 reveals a long GeGe bond length of 245 pm and a large trans‐bent angle of 42°. Air‐oxidation of (Z)‐9 takes place with retention of configuration at the germanium atoms to provide the corresponding substituted (Z)−2,4‐digerma‐1,3‐dioxetane (Z)‐10. Treatment of 5 with the stannylene :Sn[N(SiMe3)2)2 gives, as a final product, the hydridodisilylstannane 12. The structures of (Z)‐10 and 12 were also determined by X‐ray crystallography.
Betulin binds to melanocortin receptors and antagonizes α‐melanocyte stimulating hormone induced cAMP generation in mouse melanoma cells
Authors: Muceniece Ruta , Saleniece Kristine , Riekstina Una , Krigere Liga , Tirzitis Gunars , Ancans Janis
Published: July 2007

Betulin is a principal component of birch bark and is known to possess a broad range of biological activities, including antiinflammatory, antiviral and anticancer actions. The present study was carried out in vitro to clarify the influence of betulin on melanocortin (MC) receptor‐ergic signalling by using COS‐7 cells transfected with corresponding human MC receptor DNA. The results showed that betulin binds to the human melanocortin MC1, three to five receptors with selectivity to the MC1 subtype (Ki value 1.022 ± 0.115 µM). Betulin binds to the MC receptors with the following potency order—MC > MC3 > MC5 > MC4. Betulin itself does not stimulate cAMP generation, however, it slightly antagonizes α‐melanocyte‐stimulating hormone (α‐MSH)‐induced cAMP accumulation in the mouse melanoma cell line B16‐F1. As a water‐insoluble substance, betulin was dissolved in DMSO therefore DMSO competition with the labelled ligand NDP‐MSH for the binding to the MC receptors was tested in the identical experimental set‐up. We found that DMSO competes for binding to all the MC receptor subtypes, at 20% concentration and above. Selectivity for one or another receptor subtype was not observed. We have demonstrated for the first time, the ability of the plant compound betulin to bind to the MC receptors. One may suggest MC receptor MC1 subtype as the essential target for the antimelanoma action of betulin and its structurally close molecules such as betulinic acid. Moreover, we have found a new non‐peptide small molecule MC mimetic, that is betulin. Thus, we report a new chemical motif for the binding to the MC receptors that could be used as a template for the search of more selective MC mimetics. Copyright © 2007 John Wiley & Sons, Ltd.
The Path Ahead for Ionic Liquids
Authors: Joglekar H. G. , Rahman I. , Kulkarni B. D.
Published: July 2007

Ionic liquids are designer molecules which can efficiently replace the conventional organic solvents used in chemical processes and operations. Although a number of such applications have been reported in the literature for almost a decade, very few have actually been commercialized. This paper details the different applications claimed and examines the issues and barriers which obstruct the rapid commercialization of ionic liquids. It identifies further courses of action required for the assessment and realization of the advantages of ionic liquids.
Adsorption of Pb2+ on Chitosan Cross‐Linked with Triethylene‐Tetramine
Authors: Tang X.‐H. , Zhang X.‐M. , Guo C.‐C. , Zhou A.‐L.
Published: July 2007

A novel triethylene‐tetramine cross‐linked chitosan (CCTS) was synthesized via the cross‐linking of triethylene‐tetramine and epichlorohydrin activated chitosan. Its structure was characterized by elemental analysis, infrared spectroscopy and X‐ray diffraction analysis, and the surface topography was determined with ESEM. The results were in agreement with expectations. The capacity of CCTS to adsorb Pb2+ ions from aqueous solutions was examined, and equilibrium and kinetic investigations were undertaken. The adsorption isotherms were fitted well by the Langmuir equation (R > 0.999). The maximum adsorbed amount, at pH 5.5, with an initial concentration of 3 mmol/L (621 ppm), was 378.8 mg/g. The adsorption process could be best described by a second‐order equation (R = 1). This suggests that the rate‐limiting step may be the chemical adsorption (chemisorption) step and not the mass transport. The separation factor used was 0 < RL < 1. Therefore, it can be concluded that CCTS is an effective adsorbent for the collection of Pb2+.
CFD Simulation of Mass Transfer Efficiency and Pressure Drop in a Structured Packed Distillation Column
Authors: Haghshenas Fard M. , Zivdar M. , Rahimi R. , Nasr Esfahani M. , Afacan A. , Nandakumar K. , Chuang K. T.
Published: July 2007

The pressure drop and mass transfer efficiency for two‐phase flow in a structured packed column were simulated using a commercial CFD package, CFX version 10. The distillation of the methanol/isopropanol system was carried out in a 0.073 m diameter column, with an element composed of a ceramic structured packing and 0.053 m in height. The Height Equivalent to Theoretical Plate (HETP) value varied from 0.106–0.146 m. Pressure drop experiments were measured with an air/water system. The pressure drops at the flooding and loading points were ca. 173 and 580 Pa/m of packing, respectively. HETPs and pressure drops calculated from the Computational Fluid Dynamics (CFD) model were compared to their experimental counterparts. The average relative error between CFD predictions and the experimental data for the prediction of dry pressure drop, irrigated pressure drop and mass transfer efficiency are 20.3 %, 23 % and 9.15 %, respectively. In all cases, the CFD predictions show a good agreement with the experimental data, indicating that CFD is a reliable, cost saving and suitable technique for the design and optimization of separation processes.
Capillary Pressure Estimation Using Statistical Pore Size Functions
Authors: Ghazanfari M. H. , Rashtchian D. , Kharrat R. , Vossoughi S.
Published: July 2007

Capillary pressure curves, which have been employed for a long period of time by researchers interested in pore size distribution, are commonly obtained from experimental measurements. The dynamic capillary pressure that influences the flow is affected by many factors including the pore size characteristics and pore scale dynamics. Hence, it is important to investigate the variation of the estimated pore size distribution with capillary number. In this study, a glass type micromodel is considered as the porous media sample. A parametric probability density function is proposed to express the pore size distribution of the porous model, which is also measured using an image analysis technique. The capillary pressure saturation mathematical model is developed by integrating the pore size distribution function. Model parameters with a physical significance are estimated by fitting the model to the measured capillary pressure data at different capillary numbers. The results of capillary pressure obtained are well matched to the measured values. The results show that the trends of the extracted pore size distribution curves have similar trends, but they are not exactly the same. Therefore, the dynamic capillary pressure data alone are not sufficient for estimation of the pore size distribution. As a related development, the prediction of the capillary pressure curves based on measured pore size distributions is also presented. The proposed probability distribution function has the flexibility of representing a wide variety of pore size distributions.
3‐D Simulations of an Internal Airlift Loop Reactor using a Steady Two‐Fluid Model
Authors: Huang Q.‐S. , Yang C. , Yu G.‐Z. , Mao Z.‐S.
Published: July 2007

Three‐dimensional (3‐D) simulations of an internal airlift loop reactor in a cylindrical reference frame are presented, which are based on a two‐fluid model with a revised k‐ϵ turbulence model for two‐phase bubbly flow. A steady state formulation is used with the purpose of time saving for cases with superficial gas velocity values as high as 0.12 m/s. Special 3‐D treatment of the boundary conditions at the axis is undertaken to allow asymmetric gas‐liquid flow. The simulation results are compared to the experimental data on average gas holdup, average liquid velocity in the riser and the downcomer, and good agreement is observed. The turbulent dispersion in the present two‐fluid model has a strong effect on the gas holdup distribution and wall‐peaking behavior is predicted. The CFD code developed has the potential to be applied as a tool for scaling up loop reactors.
A Sensitive Fluorescence Anisotropy Method for Point Mutation Detection by Using Core–Shell Fluorescent Nanoparticles and High‐Fidelity DNA Ligase
Authors: Deng Ting , Li Jishan , Jiang Jian‐Hui , Shen Guo‐Li , Yu Ru‐Qin
Published: July 2007

The present study reports a proof‐of‐principle for a sensitive genotyping assay approach that can detect single nucleotide polymorphisms (SNPs) based on fluorescence anisotropy measurements through a core–shell fluorescent nanoparticles assembly and ligase reaction. By incorporating the core–shell fluorescent nanoparticles into fluorescence anisotropy measurements, this assay provided a convenient and sensitive detection assay that enabled straightforward single‐base discrimination without the need of complicated operational steps. The assay was implemented via two steps: first, the hybridization reaction that allowed two nanoparticle‐tagged probes to hybridize with the target DNA strand and the ligase reaction that generated the ligation between perfectly matched probes while no ligation occurred between mismatched ones were implemented synchronously in the same solution. Then, a thermal treatment at a relatively high temperature discriminated the ligation of probes. When the reaction mixture was heated to denature the duplex formed, the fluorescence anisotropy value of the perfect‐match solution does not revert to the initial value, while that of the mismatch again comes back as the assembled fluorescent nanoparticles dispart. The present approach has been demonstrated with the discrimination of a single base mutation in codon 12 of a K‐ras oncogene that is of significant value for colorectal cancers diagnosis, and the wild type and mutant type were successfully scored. Due to its ease of operation and high sensitivity, it was expected that the proposed detection approach might hold great promise in practical clinical diagnosis.
Efficient representation of nonreflecting boundary conditions for the time‐dependent Schrödinger equation in two dimensions
Authors: Jiang Shidong , Greengard Leslie
Published: July 2007

We present a fast algorithm for the evaluation of exact, nonreflecting boundary conditions for the time‐dependent Schrödinger equation in two dimensions on the unit circle. After separation of variables, the exact outgoing condition for each Fourier mode contains a nonlocal term that is a convolution integral in time. The kernel for that convolution is the inverse Laplace transform of the logarithmic derivative of a modified Bessel function, and the convolution integral can be split into two parts: a local part and a history part, which can be treated separately. The local part is easily handled by an appropriate quadrature. For the history part, we show that the convolution kernel can be well approximated by a sum of exponentials. Once such a representation is available, the convolution integrals can be evaluated recursively, reducing the cost from O(N2) work to O(N), where N is the number of time steps. The main technical development lies in the uniform rational approximation of the logarithmic derivative of the modified Bessel function Kν(√is). © 2007 Wiley Periodicals, Inc.
Time domain analysis and design of multirate wave digital filters
Authors: Fahmy M. F. , El‐Wardaney A. , El‐Gayed N. A. , Sobhy M. I.
Published: July 2007

A generalized time domain approach is described for the analysis and design of wave digital filters capable of performing sampling rate alterations whether integer or non‐integer. It is based on sequential computation of the filter's system response; then this discrete response is reduced to a rational function form. the proposed approach is characterized by its simplicity as well as its ability to analyse and design multistage, multirate wave digital structures. Illustrative examples are also given.
Switched‐capacitor neural networks for differential optimization
Authors: Cichocki A. , Unbehauen R.
Published: July 2007

The primary goal of this paper is to solve some types of optimization problems whose objective functions and constraints are smooth and continuously differentiable and which are not suited for digital signal processing. the optimization problems are mapped into systems of first‐ and second‐order non‐linear ordinary differential equations and/or systems of difference equations. These systems of equations are simulated by appropriate switched‐capacitor (SC) circuits employing some neural network (neurobiological) principles. New switched‐capacitor architectures for on‐line solving of non‐linear optimization problems are proposed and their properties are investigated. Various circuit structures are investigated to find which are best suited for SC CMOS implementation. the structures developed exhibit a high degree of modularity, and a relatively small number of basic building blocks (computing cells) are required to implement effective and powerful optimization algorithms. Basic mathematical operations, e.g. multiplication, addition and non‐linear scaling transformation, are accomplished employing advanced SC techniques. the validity and performance of the circuit structures developed are illustrated by intensive computer simulations employing TUTSIM and NAP programmes.
Frequency compensation of MOS operational transconductance amplifiers
Authors: Kothapalli Ganesh
Published: July 2007

Operational transconductance amplifiers (OTAs) can be compensated by a capacitor placed in the differential‐to‐single‐ended (D/SE) conversion stage. the concept involved in shaping the magnitude and phase‐frequency response of OTAs is to realize a low‐frequency zero such that the effects of double poles prior to unity gain are not felt. It is sometimes possible to meet the objectives of gain and phase margin by providing compensation in more than one stage. the flexibility of the scheme devised is demonstrated by suggesting alternative ways (two‐capacitor compensation) to realize desired root locations. the key point in achieving proper compensation always remains the appropriate choice of capacitor size. Thus the size of the compensation capacitor and placement of the compensation network have been presented here from the context of suitability for implementation in MOS foundries. the compensation schemes discussed are suitable in the second or additional gain stages.
Global properties of continuous piecewise linear vector fields. Part I: Simplest case in ℝ2
Authors: Lum Robert , Chua Leon O.
Published: July 2007

Among non‐linear vector fields, the simplest that can be studied are those which are continuous and piecewise linear. Associated with these types of vector fields are partitions of the state space into a finite number of regions. In each region the vector field is linear. On the boundary between regions it is required that the vector field be continuous from both regions in which it is linear. This presentation is devoted to the analysis in two dimensions of the simplest possible types of continuous piecewise linear vector fields, namely linear vector fields possessing only one boundary condition. As a practical concern the analysis will attempt to ask and answer questions raised about the existence of steady state solutions. Since the local theory of fixed points in a linear vector field is sufficient to determine the stability of fixed points in a piecewise linear vector field, most of the steady state behaviour to be studied will be towards limited cycles. the results will present sufficient conditions for the existence, or non‐existence as the case may be, of limit cycles. Particular attention will be paid to the domain of attraction whenever possible.

With these results qualitative statements may be made for piecewise linear models of many physical systems.