bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and Structure of Methoxybis[tris(trimethylsilyl)silyl]methane – The First Geminal Di(hypersilyl) Compound with a Central Carbon Atom
Authors: Jeschke Elke , Gross Thoralf , Reinke Helmut , Oehme Hartmut
Published: July 2007

Methoxy‐bis[tris(trimethylsilyl)silyl]methane (4), the first compound bearing two hypersilyl groups at a carbon atom, was synthesized by the reaction of tris(trimethylsilyl)silyllithium with dichloromethyl methyl ether. As a byproduct of the reaction, 1,2‐dimethoxy‐1,2‐bis[tris(trimethylsilyl)silyl]‐ethane (5) could be identified. Possible pathways leading to 4 and 5 are discussed. The structure of 4, elucidated by an X‐ray crystal structure analysis, is characterized by tremendous distortions of the molecular skeleton due to the spatial demand of the two extended hemispherical (Me3Si)3Si groups. For example, the central Si–C–Si angle is widened to 132.7°, the trimethylsilyl groups of the two hypersilyl substituents are pressed together to give an average Si–Si–Si angle of 105.6°, and the methoxy carbon atom and the nearest neighboring trimethylsilyl carbon atom approach to a distance of 3.25 Å, i.e. approx. 19% less than the sum of the van der Waals radii of two methyl groups.
Iron‐Mediated Conversions of Eucarvone‐Derived Cationic Dienyl Complexes
Authors: Hirschfelder Andreas , Drost Daniel , Meinhardt Sven , Eilbracht Peter
Published: July 2007

Cationic cycloheptadienyl iron complexes with new substitution patterns are generated by starting from the eucarvone complex 5 and the analogous triphenyl phosphite complex 6. These complexes are converted with different nucleophiles. Regioselectivity of the nucleophilic attack depends on the substitution pattern of the seven‐membered ring. A new type of cationic system 7b, bearing an alkoxy substituent at C‐1, was treated with nucleophiles leading to the ipso adducts of type 10. Unexpected attack at the central C‐3 of the dienyl moiety is observed during the conversion of cationic complexes of type 9 with nucleophiles. The diene iron complexes, obtained in these reactions, can be converted to substituted cycloheptadienes by oxidative decomplexation, as shown by a selected example.
Novel Inorganic (Carbon‐Free) Chelate Rings: Tris(chelate) Compounds of [N‐(Diphenylphosphinoselenoyl)‐P,P‐diphenylphosphinoselenoic amidato‐Se, Se′] with MIII (M = Sb, Bi, In)
Authors: Cea‐Olivares Raymundo , García‐Montalvo Verónica , Novosad Josef , Woollins J. Derek , Toscano Rubén A. , Espinosa‐Pérez Georgina
Published: July 2007

The [(SePPh2)2N]− ligand 1c forms stable tris(chelates) with the SbIII, BiIII, and InIII ions. The crystal and molecular structures of the resulting compounds 3, 4, and 5 were determined by X‐ray diffractometry. The coordination geometry around the metal centers can be described as a distorted octahedron. This feature and the results obtained by comparing the structures with their sulfur and oxygen analogs lead us to conclude that in both SbIII and BiIII compounds the arrangement around the metals suggests a stereochemically nonactive electron lone pair.
Synthesis and Characterization of Novel Phthalocyanines with Four 16‐Membered Diazadithia Macrocycles
Authors: Yilmaz Ismail , Bekaroǧlu Özer
Published: July 2007

Metal phthalocyanines (M = Cu, Ni, Co) 3‐5 bearing four 16‐membered diazadithia macrocycles at the peripheral positions were prepared. Detosylation with concentrated sulfuric acid afforded products containing both sulfonated groups on the aromatic rings of the macrocyclic substituents which are excellently soluble in water and donor sites for binding four CuII ions to give a pentanuclear complex.
Synthesis, Structure and Vibrational Spectra of Ba14InP11
Authors: Carrillo‐Cabrera Wilder , Somer Mehmet , Peters Karl , von Schnering Hans Georg
Published: July 2007

Ba14InP11 was prepared from the elements in a sealed stainless steel ampoule at 1345 K. The compound is black, brittle and very sensitive to air and moisture. Ba14InP11 crystallises in the tetragonal Ca14AlSb11 type (space group I41/acd, No. 142; a = 17.097 (2) Å, c, = 8, Pearson code tI208). The structure contains isolated P3‐, linear [P3]7‐ and tetrahedral [InP4]9‐ anions. The X‐ray structure analysis and the vibrational spectra show that the [P3]7‐ polyanion is strongly asymmetric with d(P–P) = 2.28 Å and 4.10 Å, corresponding to a [P2]4‐ dumbbell weakly coupled to a single p3‐ anion. The tetraphosphidoindate(III) anion [InP4]9‐ is slightly compressed along the 4 axis, with bond lenght d(In–P) = 2.71 Å. It is shown that the structure is hierarchically related to that of Cu2O, with two interpenetrating frameworks, in which the O and Cu atoms are replaced by condensed [InP4/2] tetrahedron and [BaP4P2/2] octahedra, respectively. Both frameworks are meso configured, containing alternate R and S fragments. The other Ba cations envelop the P6 octahedra and P3 triads forming condensed cubes, tetragonal antiprisms and bicapped trigonal prisms. Therefore, the structure also forms a heterogeneous framework of centred PBa8/2tap tetragonal antiprisms and BaBa8/2cub cubes, consisting of two interpenetrating enantiomorphic nets (R and S) similar to those in the cubic phase RhBi4.
Hydrolysis of Esters and Amides by the Metallo Nucleophile TpCum,MeZn–OH
Authors: Ruf Michael , Vahrenkamp Heinrich
Published: July 2007

The molecular zinc hydroxide complex TpCum,MeZnOH [1, TpCum,Me = tris(3‐cumenyl‐5‐methylpyrazolyl)hydroborate] is a powerful nucleophile. It effects stoichiometric hydrolysis of activated esters RCOOX and amides RCONHX in nonaqueous media. The cleavage products are TpCum,MeZnOCOR and HOX or H2NX, resp. Two of them (TpCum,MeZnOCOCH2‐CH2OH resulting from propiolactone and TpCum,MeZnOCOCF3 resulting from trifluoroacetamide) were characterized by crystal structure determinations.
Palladium‐Catalyzed Reactions in Industry, 4[]. Synthesis of New Palladium Catalysts: First Isolation and Characterization of all Intermediates in a Cyclopalladation Reaction
Authors: Beller Matthias , Riermeier Thomas H. , Haber Steffen , Kleiner Hans‐Jerg , Herrmann Wolfgang A.
Published: July 2007

In order to synthesize chiral palladacycles for stereoselective C–C coupling reactions we studied the cyclopalladation of P‐chiral phosphanes 2 and 3. New palladium complexes of the type L2PdX2 (6, 8) and LXPd–μ‐X2–PdXL (5, 9, X = Cl; L = 2, 3) were isolated. A detailed study of the reactivity of all intermediates towards cyclopalladation proved the mechanism of cyclometalation reactions of o‐tolylphosphanes for the first time. Different deuteration experiments clearly demonstrated the higher reactivity of dimeric palladium complexes towards metalation compared to monomeric species. In agreement with this observation only 5 and 9 gave the cyclopalladated products 4 and 10 as revealed by FAB mass spectrometric investigations. Under the described reaction conditions the synthesis of the corresponding palladacycles 4, 10 is not possible because cyclometalation is a reversible process with LXPd–μ–X2–PdXL as thermodynamic more stable products. The results demonstrate the importance of free coordination sites on the metal atom for cyclometalation reactions or more general CH activation processes.
The d2‐M(NR)2 Fragment, High Valent and Low Valent Organometallic Equivalents, and an Unusual Mode of Ethylene Complexation
Authors: Radius Udo , Hoffmann Roald
Published: July 2007

We report approximate molecular orbital calculations on models of the ethylene complex W(NMes)2(PMe3)2(η2‐C2H4) 1. The ethylene unit in 1 is oriented perpendicular to the equatorial plane – an unusual orientation for trigonal bipyramidal L4M‐(η2‐C2H4) complexes. In order to understand the bonding in 1, the tungsten fragment W(NR)2L2 is discussed in some detail and we compare the “high valent” ethylene complex 1 and the “low valent” olefin complex Fe(CO)4(η2‐C2H4). An analysis of π‐bonding shows that the metal nitrogen bond in the cis,‐[M(NR)2] unit is less than a triple bond, and the d2‐[M(NR)L2] fragment is more like a 16 than an 18 valence electron fragment. The nature of the occupied d‐orbital explains the opening of the angle E–M–E in trigonal bipyramidal complexes d2‐cis‐M(E)2L3. Both C2v fragments d2‐W(NR)2L2 and d8‐Fe(CO)4 have characteristic frontier orbitals, qualitatively similar to the frontier orbitals of CH2. These orbitals guide the ethylene ligand into or out of the equatorial plane. The general analysis leads to the conclusion that dn (n > O) “high valent” complex fragments are actually better back‐bonding donors for π‐acidic ligands. For 1, we detect also another mininum on the energy surface – the olefin ligand is now oriented parallel to the equatorial plane. This raises the fascinating possibilities of the existence of multiple conformational minima for some transition metal ethylene complexes.
Alkylammonium Hexachlorometallates, IV. Synthesis and Crystal Structure of Bis(1,4‐diammoniobutane) Diaquahydrogen Hexachlororhodate(III) Dichloride, [H3N–(CH2)4– NH3]2[H5O2][RhCl6]Cl2
Authors: Frank Walter , Reiß Guido J.
Published: July 2007

Bis(1,4‐diammoniobutane) diaquahydrogen hexachlorohodate(III) dichloride, [H3N–(CH2)4 –NH3]2[H5O2][RhCl6]Cl2 (1), was synthesized by the reaction of rhodium(III) chloride with 1,4‐diaminobutane dihydrochloride in concentrated hydrochloric acid. The red compound slowly decomposes at room temperature, but is stable for months and up to 106°C (DTA) under hydrogen chloride. Crystals of 1 were obtained by diffusion‐controlled crystallization (space group P,1¯). The solid‐state structure can be considered as a sequence of layers linked by hydrophobic interactions between the aliphatic chains of the 1,4‐diammoniobutane ions. Within these layers the hydrophilic building blocks (hexachlororhodate and chloride anions, the diaquahydrogen cations and the ammonio groups of the diammoniobutane cations) are connected by a complex system of OHCl and NHCl hydrogen bonds. The H5O2+ ion has a crystallographically imposed Ci symmetry and shows the typical 1:1 disorder of the central hydrogen atom for a symmetrically strong [OO 2.406(10) Å] doubleminimum potential O–H–O bond.
The Synthesis, Structural Analysis and Magnetic Properties of a New Mixed Metal Ferrite Ba3Fe24Ti7O53
Authors: Adams Richard D. , Layland Ralph , Payen Christophe
Published: July 2007

A new mixed metal titanate Ba3Fe24Ti7O53, 1 was obtained by heating stoichiometRic mixtures of BaCO3, Fe3O4 and TiO2 to 1375°C for 48 h. Compound 1 was characterized by single crystal x‐ray diffraction analysis. Two of the barium ions lie in a network of channels in the bc crystallographic plane. The iron and titanium atoms were refined in a random distribution in 16 independent MO6 octahedral sites and 2 MO4 tetrahedral sites. Magnetization measurements reveal a strong magnetic ordering up to 600 K. M vs. H loop measurements show no hysteresis effects.
The Phosphonate‐Phosphate‐ and Phosphate‐Phosphonate Rearrangement and Their Applications, 4. Deprotonation of Secondary Benzylic Phosphates — Configurationally Stabile Benzylic Carbanions with a Diethoxyphosphoryloxy Substituent and Their Rearrangement to Optically Active Tertiary α‐Hydroxyphosphonates
Authors: Hammerschmidt Friedrich , Schmidt Susanne
Published: July 2007

Optically active alcohols (ee ≥ 98%) such as 1‐phenylpropanol, 1‐(2‐naphthyl)ethanol, 1‐tetralol, and 1‐indanol were transformed into diethyl phosphates 7a–d. sBuLi/TMEDA — induced phosphate—phosphonate rearrangement in diethyl ether furnished tertiary α‐hydroxyphosphonates 8a–d of high enantiomeric purity (ee 94–98%) in yields of 43–83% with retention of configuration. The enantiomeric excesses were determined by using homochiral t‐butyl(phenyl)phosphinothioic acid as chiral solvating agent.
Reactions of (CF3)2BNMe2 with ω‐Halonitriles — Crystal and Molecular Structure of [cyclo‐C3H4(CN)](CF3)2B·NHMe2
Authors: Brauer David J. , Bürger Hans , Dittmar Thomas , Pawelke Gottfried
Published: July 2007

Dimethylaminobis(trifluoromethyl)borane, (CF3)2BNMe2 (A), reacts with Cl(CH2)3CN to yield [Cl(CH2)2CH(CN)](CF3)2B·NHMe2 (1) whereas Br(CH2)3CN and A combine in a 1:2 ratio to form [cyclo‐C3H4(CN)](CF3)2B·NHMe2 (2) and Br(CF3)2B·NHMe2. Br(CH2)nCN and A yield [Br(CH2)n‐1 CH‐(CN)](CF3)2B·NHMe2, n=4 (3), n=5 (4) and n=6 (5). Compound 2 and (NCCH2)CF3)2B·NHMe2 can be alkylated at nitrogen with CH3I/KOH in ether to yield [cyclo‐C3H4(CN)]‐(CF3)2B·NMe3 (6) and (NCCH2)(CF3)2B·NMe3 (7), respectively. treatment of 1 and 3 with hydroxide in ether gives the respective five‐ and six‐membered heterocycles (CF3)2 (8) and (9). Reduction of the nitrile group with (iBu)2Alh in CH2Cl2 at –50°C followed by hydrolysis furnishes the corresponding aldehydes (OCHCH2) (CF3)2B·NMe3 (10), [cyclo‐C3H4(CHO)](CF3)2B·NMe3 (11) and (12). The structure of 2 was determined by an X‐ray investigation.
Tripod‐Rhodium‐COD‐Komplexe: Synthese, Struktur, Dynamik und Katalyse
Authors: Scherer Johannes , Huttner Gottfried , Walter Olaf , Janssen Bernd Christian , Zsolnai Laszlo
Published: July 2007

Tripod Rhodium COD Complexes: Synthesis, Structure, Dynamics and Catalysis

The reaction of the tripod ligands R′C(CH2PR2)3 (1a–c) and X2POCH[CH2P(Ph)2]2 (2a–c) with [RhI(COD)Cl]2] is investigated. It yields tripod rhodium COD complexes [(1a–c)RhI(COD)]Y (3a–c) and [(2a–c)RhI(COD)]Y [4a–c; Y = B(Ph)4, PF6]. The tripod ligand is coordinated by all three donor groups in each case, irrespective of the different donor capabilities of the coordinating groups. The solid state structure of compounds 3a–c and 4a is determined by X‐ray analysis. The observed coordination polyhedra delineate the variation from the idealized trigonal bipyramide to an idealized quadratic pyramide. In solution the analysis of the NMR spectra shows a rapid intramolecular interconversion according to a turnstile pseudo rotation. The complexes 3a and 4a are found to be catalysts for the hydrogenation of prochiral olefines.
A Theoretical Investigation of Cycloadditions of Hydrogen Isocyanide to CH2X and PHX Dipolarophiles (X = CH2, NH, O, SiH2, PH, S)
Authors: Nguyen Minh Tho , Keer Annik Van , Vanquickenborne Luc G.
Published: July 2007

We performed a systematic investigation of [2 + 1] cycloadditions of HNC to dipolarophiles of the type CH2X and PHX with XCH2, NH, O, SiH2, PH, and S, as well as HNNH and H2SiSiH2. Ab initio MO calculations at the QCISD(T)/6‐311G(d,p)/MP2/6‐31G(d,p)+ZPE level were applied to construct the minimum‐energy reaction pathways. Calculated results concerning the regiochemistry of the approaches and the stereochemistry of the product formation were analyzed in relation with established concepts such as frontier orbital, net charge distribution and stereoelectronic effect. For some systems, up to four distinct transition structures for cycloaddition were found. In general, there is a certain similarity between the behavior of both C and P series of dipolarophiles. The characteristics of the transition structures can be, in most cases, recovered by using qualitative concepts. The [2 + 1] cycloadditions are highly regioselective and stereospecific. Silicon‐containing dipolarophiles are particularly attractive as they exhibit very small energy barriers to addition to isocyanides.
Chemical Interconversions in the System TP*Zn/CO2/Alcohol [Tp* = Substituted Tris(pyrazolyl)borate]
Authors: Ruf Michael , Schell Friedrich Alexander , Walz Rainer , Vahrenkamp Heinrich
Published: July 2007

The zinc hydroxide complexes Tp*Zn–OH with TpCum,Me = tris(3‐cumenyl‐5‐methylpyrazolyl)borate and TptBu,Me = tris(3‐tert‐butyl‐5‐methylpyrazolyl)borate can be converted to the alkyl carbonate complexes Tp*Zn–OCOOR by reaction with dialkyl dicarbonates or with alcohol and CO2. An alternative formation reaction is the treatment of the pyrazolyl borate with zinc perchlorate and potassium carbonate in alcohol. The interconversion between TpCum,MeZn–OH and TpCum,MeZn–OCOOMe in methanol‐containing solution can be repeatedly performed in both directions by bubbling either CO2 or N2 through the solution. The alkyl carbonate complexes show a variable sensitivity towards hydrolytic destruction with reformation of the hydroxide complexes. The complexes TptBu,MeZn–OCOOR (R = Me, Et) release CO2 under high vacuum to form the alkoxide complexes TptBu,Me‐Zn–OR, which could not be obtained pure due to their extreme water sensitivity. Indirect evidence for their existence is also obtained by the reaction between TpCum,MeZn–OCOOMe and methyl iodide, forming TpCum,MeZn–I and dimethyl ether. The Zinc hydroxide complexes catalyse the formation of diethyl carbonate from ethanol and CO2.
Lithium 2,2,6,6‐Tetramethylpiperidinoselenolate: An Unsymmetrical Dimer with an Unusually Coordinated Lithium
Authors: Nothegger Thomas , Wurst Klaus , Probst Michael , Sladky Fritz
Published: July 2007

Lithium 2,2,6,6‐tetramethylpiperidide inserts elemental selenium into its Li–N bond with the formation of lithium 2,2,6,6‐tetramethylpiperidinoselenolate 1. In the crystal 1 is an unsymmetric dimer. One lithium atom is coordinated tetrahedrally by two molecules of tetrahydrofuran and two selenium atoms, the other lithium atom exhibits an approximately rectangular‐planar coordination by two N,Se‐chelating groups. The lithium atoms are bridged by two selenium atoms thus forming a planar Li2Se2 core. Ab initio Hartree‐Fock calculations show 1 and the hypothetical symmetric dimer 2 to be of equal energy, whereas the non‐chelated dimer 3 is of distinctly higher energy. Exclusive crystallization of 1 is most likely a consequence of its large dipole moment of 6.18 D. Calculations also show that the deformation of the observed geometry around the uniquely coordinated lithium atom in 1 towards distorted tetrahedral or complete planarity leads to an increase of energy. Excessive charge transfer from selenium to nitrogen explains the overwhelming tendency for the N,Se‐chelating bonding.
Pyrazolate‐Based Oligonuclear Copper and Silver Complexes with N/S Coordination Spheres
Authors: Meyer Franc , Jacobi Albrecht , Zsolnai Laszlo
Published: July 2007

A series of pyrazole‐based potential ligands bearing thioether substituents in 3‐ and 5‐positions of the heterocycle was synthesized [3,5‐bis(RSCH2)‐pyzH R=Ph (1aH), PhCH2 (1bH), iPr (1cH), tBu (1dH)]. These ligands afford oligonuclear Cu1 and Ag1 coordination compounds [LCu]x (2a–c, L = 1a ‐ c) and [LAg]x (3a‐d, L = 1a‐d), respectively. The single crystal X‐ray analysis of 3c shows the presence of trimeric planar arrays of N,N′‐bridging pyrazolates and linear coordinated silver ions, with each two of the trinuclear moieties being linked by two unsupported short intermolecular Ag…Ag contacts [3.041(1) Å]. Molecular‐weight determinations for 2a (THF) and 3c (toluene) indicate that hexanuclear entities are preserved in solution. Starting from 1bH the CuII complex [(1b)2Cu2](BF4)2 (4) was synthesized. According to an X‐ray crystal structure analysis it consists of dinuclear molecules with two bridging pyrazolates, distorted square planar N2S2 coordination spheres for Cu11 and an axially bridging tetrafluoroborate. Magnetic susceptibility data reveal an antiferromagnetic exchange (J = ‐206 cm−1) that is among the highest found for doubly pyrazolate bridged dicopper(II) complexes, which is rationalized on the basis of the rather symmetric dinuclear core of 4. The irreversibility of the electrochemical reduction and oxidation processes for the CuII and CuI compounds, respectively, is explained by the inability of the respective coordination framework to adapt to different geometric preferences.
Synthesis and Reactions of Bis (4,5‐benzo‐1,3‐dioxa‐2‐phospholano)dichlormethane
Authors: Krill Jochen , Shevehenko Igor V. , Fischer Axel , Jones Peter G. , Schmutzler Reinhard
Published: July 2007

The title compound 3 was formed in the reaction of Cl2PCCl2PCl2 (2) with catechol in the presence of triethylamine. The reaction of 3 with tetrachloro‐o‐benzoquinone (TOB), 4, led to the σ3P/σ5P‐species 5, and the σ5P/σ5P‐species 6a/6b. 5 was stable only in solution, and its existence and identity are postulated on the basis of its 31P‐NMR spectrum. The structure of 6a/6b could not be assigned unambiguously to one isomer. The reaction of 6a/6b with water yielded the phosphorate 10. The structures of 3 and 10 were determined by single crystal X‐ray methods. A wide PCP angle (123.2°) was observed in 3. The cation of 10 is a centrosymmetric, protonated DMF dimer with OO 241.3 pm.
Olefin Carbonylation Catalysis with Cationic Palladium Complexes: Selectivity and Possible Intermediates
Authors: Sperrle Martin , Consiglio Giambattista
Published: July 2007

Palladium complexes L2PdX2 containing various group Va ligands and weakly coordinating anions are active catalysts for the carbonylation of olefin substrates. These catalytic systems, though gaining significance in industry for the synthesis of polyketones, are normally characterised by a low chemoselectivity. This derives from the numerous possibilities for initiation and termination reactions which lead to different catalytic cycles and from facile multiple alternating insertion reactions of olefins and carbon monoxide. Based on experiments carried out under conditions of low selectivity and on previously published data, the factors involved in the control of the regio‐, chemo‐ and stereoselectivity for those reactions are discussed, taking current ideas and model studies involving the above palladium complexes into consideration.
1‐Hexene Hydroformylation with the Rhodium (I) Triphosphane Complex [Rh(CO){PhP(CH2CH2PPh2)2}]PF6: An In Situ Study Using High‐Pressure NMR Spectroscopy
Authors: Bianchini Claudio , Meli Andrea , Peruzzini Maurizio , Vizza Francesco , Frediani Piero
Published: July 2007

The rhodium‐catalyzed hydroformylation of 1‐hexene in THF with the linear triphosphane PhP(CH2CH2PPh2)2 [PP,] has been studied both in situ and in high‐pressure autoclaves. Sapphire NMR tubes with titanium valves have proved useful for studying the in situ reactions under conditions of relatively high syngas pressure (30–90 atm H,/CO) and temperature (60–100 C). Under conditions conducive to effective hydroformylation, the catalyst precursor [ (PP,)Rh(CO)]+ is quantitatively converted to the dicarbonyl [ (PP,)Rh(CO),]+, which is also the termination product of the catalysis. Irrespective of the syngas composition and of the total pressure, the dicarbonyl complex is the only phosphorus‐containing species detectable on the NMR time‐scale during the course of the isomerization and hydroformylation of the alkene. The PP2‐Rh catalytic system exhibits some peculiar features that may be summarized as follows. (i) Very high partial pressures of CO (120 atm) neither inhibit the hydroformylation nor affect the n/i selectivity; (ii) alkene hydrogenation occurs neither at very high partial pressures of H, (120 atm) nor in the absence of added CO; (iii) the isomerization rate is slightly faster than that of hydroformylation; (iv) terminal and internal alkenes (2‐, 3‐hexenes) are hydroformylated with comparable rates. Various control experiments have been carried out using in‐situ NMR, as well as batch experiments under different reaction conditions or with different catalyst precursors. Despite these extensive studies, unambiguous conclusions about the catalysis mechanism have not been reached. In particular, the possibility that different catalysts may be operative depending on the reaction conditions cannot be ruled out. The hydroformylation results rule out the involvement of phosphane‐free “Rh‐CO” catalysts, even under conditions of very high partial pressure of CO, and point to “(PP,)Rh(CO),” catalysts with small steric hindrance over the whole range of syngas pressures investigated.
Synthesis Structure and Photoluminescence of 1,2‐Disila‐acenaphthene Si2C10H10 and 1,2‐Diaryldisilane Reference Compounds
Authors: Södner Marcus , Sandor Mario , Schier Annette , Schmidbaur Hubert
Published: July 2007

For the synthesis of the diaryldisilanes Ar–SiH2SiH2–Ar (1a, Ar = phenyl; 1b, Ar = p‐tolyl 1c, Ar = mesityl; 1d, Ar = p‐anisyl) two convenient preparative routes are reported. The crystal structures of 1c and 1d have been determined in X‐ray diffraction studies; the disilanes have a staggered transconformation with a crystallographically imposed center of inversion. For 1a–d no photoluminescence phenomena can be observed. 1,2‐Disila‐acenaphthene (2) is synthesized in acceptable yield by treatment of 1,8‐dilithionaphthalene with 1 equivalent of 1,2‐bis[((trifluoromethyl)sulfonyl)oxy]disilane Tf–SiH2SiH2–Tf. The crystal structure of 2 has been determined by X‐ray diffraction. The molecule has no crystallographically imposed symmetry but closely follows the symmetry elements of points group C2v. Solutions of 2 exhibit intense fluorescence in the near UV region at room temperature. The fluorescence spectra are discussed in comparison with data on acenaphthene and naphthalene.
Dichotomy in the Reactivity of Trivalent Phosphorus Compounds Z3P (Z = Ph, nBu, OR) Observed in the Photoreaction with a Ruthenium Complex
Authors: Yasui Shinro , Tsujimoto Munekazu , Shioji Kosei , Ohno Atsuyoshi
Published: July 2007

Solutions of tris(2,2′‐bipyridyl)ruthenium(II) dichloride (Ru2+) and various types of trivalent phosphorus compounds Z3P (Z = Ph, n‐Bu, OR; 1) in methanol have been photolyzed with visible light at 20 °C under an argon atmosphere, resulting in the oxidation of 1 to the corresponding pentavalent oxo compounds Z3PO and ligand exchange of Ru2+ with 1. The former process takes place via single‐electron transfer (SET) from 1 to Ru2+ in the photoexcited state, Ru2+*, which generates the radical cation intermediate Z3P.+ from 1. The latter results from nucleophilic attack of 1 upon Ru2+*. The results show that 1 can act either as an electron donor or as a nucleophile toward Ru2+*. The rate constants for both processes are estimated. An excellent linear correlation is found between the logarithm of the SET rate and the oxidation potential for both the aromatic and aliphatic trivalent phosphorus comparison with SET quenching by amines. On the other hand, a dualparameter correlation analysis shows that the ligand exchange is regulated by both steric and electronic factor in 1.
Synthesis, Structure, and Reactivity of Tetrakis(O,O‐phosphorus)‐Bridged Calix[4]resorcinols and Their Derivatives
Authors: Vollbrecht Alexander , Neda Ion , Thönnessen Holger , Jones Peter G. , Schmutzler Reinhard , Harris Robin K. , Crowe Lindsey A.
Published: July 2007

The synthesis and characterisation of the reactive tetrakis (O,O‐phosphorus)‐Bridged calix[4]resorcinols 3 and 4 is described. Because of its poor solubility in common organic solvents, a solid‐state NMR investigation of 3 (1H, 13C, 31P) was conducted. Reaction of 3 with MeMgl, Me3 SiMNe2, and HNMe2 furnished the η3γ3P‐substituted cavitands 5 and 6. Oxidative addition reactions of 6 with the (H2N)2C(=O)/H2O2 (1:1) adduct, tetrachloro‐o‐benzoquinone (TOB), and hexafluoroacetone (HFA) led to the η4γ5P derivative 7, and to the η5γ5P derivatives 8 and 9. An X‐ray crystal‐structure determination of the tetrakis(O,O‐phosphorus)‐bridged calix[4]resorcinol 4 has been conduced. The framework displays the cone conformation; the chlorine atoms are directed inwards.
Halogenation of 1‐Ethoxy‐1‐oxophosphindolin‐3‐one, a Potential Phosphaindigo Precursor
Authors: Vollbrecht Sebastian , Ruthe Frank , Jones Peter G. , Mont Wolf‐Walther Du , Grahn Walter
Published: July 2007

The bromination of 1‐ethoxy‐1‐oxophosphindolin‐3‐one (1) with two equivalents oi bromine occurs with elimination of hydrogen bromide and ethyl bromide, providing 2,2‐di‐ bromo‐1‐hydroxy‐1‐oxophosphindolin‐3‐one (4) in high yield. In the presence of triethylamine this process leads to 2,2‐dibromo‐1‐ethoxy‐1‐Oxophosphindolin‐3‐one (3) instead. Triethylamine deprotonates 4, providing the solid triethylammonium salt 5. Silylation of 4 with chlorotrimethylsilane leads to the trimethylsilyl ester 6. Monobromination in a two‐phase reaction allows the isolation of a mixture of isomers of 2‐bromo‐1‐ethoxy‐1‐oxophosphindolin‐3‐one (2a, b). Chlorination with chlorine furnishes 2,2‐dichloro‐1‐ethoxy‐1‐oxo‐phosphindolin‐3‐one (7). The new compounds 2–7 were characterized analytically and spectroscopically (EI‐MS, 1H, 13C and 31P NMR). The crystal structure of acid 4 was determined by X‐ray diffraction. Solid 4 consists of aryl stacks connected by chains of POH…O==P hydrogen bonds and secondary Br…Br contacts.
Generation of constituent matrices
Authors: Rao V. V. Bapeswara , Jyothirao P. A. D. , Murti V. G. K.
Published: July 2007

A simple method is outlined for evaluating the residues in a partial fraction expansion when multiple roots are present. Its application along with Frame's algorithm leads to an efficient scheme for the generation of the constituent matrices when multiple eigenvalues are present.
A new impedance‐transformation property and its applications to switching‐diode Q‐factor measurements
Authors: Morawski Tadeusz
Published: July 2007

A new property of impedance transformation is presented that can be applied to semiconductor switching‐diode Q factor measurements. The only parameter that must be known for the diode holder and the diode package is the efficiency of the energy transmission from the source of the signal to the semiconductor junction.
A graph theoretical interpretation of nonsymmetric permutation on sparse matrices
Authors: Sangiovanni‐Vincentelli A. L.
Published: July 2007

In the tableau approach to large‐electrical‐network analysis, as well as in structure analysis, the finite‐element method, linear programming etc., a very sparse linear algebraic set of equations Ax = b has to be solved repeatedly. To efficiently solve the system via Gaussian elimination, an optimization problem has to be faced: the selection of a pivot strategy to maintain the sparsity of the matrix A. It is possible also to follow a different strategy to fully exploit the sparsity of A, i.e. to transform A into an equivalent but more convenient form. Both of these problems have been studied and partially solved by means of directed graphs associated with A when symmetric permutations on A are allowed.

In this paper, a graph theoretical interpretation has been given to nonsymmetric permutations on A, which can be considered a fundamental step towards the solution of the above‐mentioned optimization problems. This interpretation is obtained through decomposition theorems on nonsymmetric permutations, correspondence theorems between column (row) permutations and topological operations on a directed graph representing A.
A theory of nonenergic N‐ports
Authors: Wyatt J. L. , Chua L. O.
Published: July 2007

A circuit element is nonenergic if the instantaneous power flow into it is always zero. Well‐known examples include the ideal diode, transformer, gyrator and circulator. Most of the interesting nonenergic elements are nonlinear N‐ports with N ⩾ 2, and many of their properties are quite counterintuitive. For example, there exists a surprisingly large class of nonenergic multiport capacitors and inductors, all of which, it turns out, are nonlinear and reciprocal. Nonenergic linear N‐ports, on the other hand, are necessarily resistive and antireciprocal.

In this paper, we present a rigorous fundamental theory of nonenergic N‐ports that results in a general canonical representation. Special canonical forms are developed for nonenergic resistors, capacitors and inductors, and numerous examples are given.
A negative‐impedance‐converter circuit for higher frequencies
Authors: Atiya F. S. , El‐Shiekh M. N.
Published: July 2007

The main weakness of the Yanagisawa negative‐impedance‐converter circuit is the large phase shift of its current conversion gain h21 at higher frequencies. The reason for this phase shift is the collector capacitances of the two transistors. The addition is suggested here of a capacitor that balances out the effect of these capacitances as far as h21 is concerned. A real and constant h21 results, up to higher frequencies. Another capacitor compensates for the effect of the transistor capacitances on h22. The remaining two h parameters need no such compensation. Experimental results confirm all these conclusions.
Bounds for the amplitude of quantization error in forced 1st‐order 2‐dimensional digital filters
Authors: Maria G. A. , Fahmy M. M.
Published: July 2007

Bounds for the amplitude of the error at the output of fixed‐point 1st‐order 2‐dimensional filters due to roundoff after multiplications are obtained. These bounds apply to the transient as well as the steady‐state response when the signal is present.
Further relationships between several types of multiparametric sensitivity
Authors: Mazzoni G. , Liberatore A.
Published: July 2007

The study of sensitivity carried out in previous work1 is resumed and generalized, both with regard to relationships with other sensitivity expressions and with regard to the extension of the study to the 3rd‐degree polynomials that appear in the transfer functions realized by active networks with nonideal operational amplifiers.

A study is made of the relationships between the various sensitivity expressions with respect both to the polynomial coefficients of the transfer function and to the physical parameters of the circuit, to show the possibility of measuring some forms of sensitivity hitherto defined analytically.

Lastly, emphasis is placed on the difference between the sensitivity of the transfer function in complex form and that of its modulus and phase with respect to the polynomial coefficients, and an attempt is made to relate them, with reference to other studies that have recently appeared in the technical literature1,3.
Recursive digital filters with low roundoff noise
Authors: Szczupak J. , Mitra S. K.
Published: July 2007

A novel method is introduced for designing recursive digital filters with very low roundoff noise. The proposed method is based on reducing the magnitudes of the noise transfer functions on the unit circle by ensuring the presence of zeros, while simultaneously synthetizing the prescribed transfer function. The final structure, which exhibits steady‐state roundoff noise with low variance, is simple and economical, and canonic with respect to delay elements, although not always canonical with respect to multipliers. An illustrative example is included. The realization method is also shown to reduce the multiplier coefficient sensitivities.
Analysis of negative‐resistance oscillators with piecewise nonlinearity
Authors: Mamola G. , Sannino M.
Published: July 2007

An iterative method of solution of negative‐resistance oscillators with piecewise‐analytical characteristics is presented. The method allows the determination of the frequency and the harmonic content of the waveform as a function of the circuit parameters and bias of the nonlinear device.

An application of the method, extended to the second order, for a polynomial characteristic limited by two straight lines is also reported. The results are compared with those obtained by numerical integration.
2‐parameter root‐loci concepts and some applications
Authors: Zeheb E. , Walach E.
Published: July 2007

Root‐locus concepts are expanded to treat characteristic expressions of systems and circuits with two parameters which vary along straight lines through the origin of the complex plane. Theorems are stated and proved by which the problem of finding the boundary of root regions of such expressions is reduced to the problem of plotting 1‐parameter root loci.

The concepts of 2‐parameter root loci are then used to investigate the absolute stability of arbitrarily passively terminated 2‐ports.

The following results are obtained by this method:

The complete root regions of the characteristic equation are found, rendering more information about the dynamic behaviour of the 2‐ports than just determining absolute stability.

A new absolute stability criterion is proved which does not necessitate checking a polynomial for nonnegativeness along the imaginary axis.

A new proof of the Llewellyn criterion is arrived at.

A numerical example is also provided for further clarification.
Synthesis of 2‐variable active RC networks
Authors: Mitra S. K. , Ahmed M. T.
Published: July 2007

A general procedure is outlined to realize an arbitrary stable 2‐variable transfer function. The complete realization utilizes only resistors, capacitive elements and operational amplifiers; moreover, it is characterized by low active and passive sensitivities. The method may easily be extended to the realization of multivariable transfer functions.
Symmetry requirements for multidimensional digital filters
Authors: Fettweis A.
Published: July 2007

Various methods for designing multidimensional digital filters exhibiting approximately circular, spherical or hyperspherical attenuation symmetry are discussed. It is shown how, by means of appropriate series expansions, symmetry requirements for filters with any number of dimensions can be fulfilled with arbitrary precision by adopting transformations of correspondingly increased degree. Some of these transformations are generalizations of the known McClellan transformation. Simple means for ensuring excellent symmetry at frequencies remote from the origin are presented.
An accurate rational 2‐port model of a class of tapered lossless and RC lines
Authors: Kumar U. , Roy S. C. Dutta
Published: July 2007

A rational 2‐port model of a class of tapered LCand RClines which includes the exponential, hyperbolic, trigonometric and square, or Bessel, lines is presented. The model for the exponential RCline (ERC), considered as an example, accurately describes the actual frequency and transient response for various values of taper factor over wide ranges of frequency and time. In an ERC notch network configuration, application of this model predicts the results very closely for various values of taper factor.
On the design of RC‐active follow‐the‐leader. Feedback filters
Authors: Gensel J.
Published: July 2007

For RC‐active filters of the ‘follow‐the‐leader’ feedback type, a synthesis procedure is presented that is suitable for application also to the general case in which differently tuned biquadratic functional blocks are used. Their losses can either be concentrated in one of the blocks, or given by a prescribed distribution.
A new generalized inverter based on the active hybrid
Authors: Atiya F. S. , Doss M. M.
Published: July 2007

The building block for the new generalized immittance inverter is a 3‐port known as the active hybrid network. One of its ports is bidirectional, and matches a design admittance y0. The second port operates in the send, while the third port operates in the receive direction. The hybrid is constructed from an op‐amp and a 5‐port network composed of a few resistors and the design admittance y0. There are two versions of the hybrid: the voltage‐inverting (i.h.) and the noninverting hybrid (n.i.h.).

The inverter consists of an i.h. and an n.i.h. connected at their unidirectional ports in a loop. The gyration admittances are actual driving‐point admittances in the circuit, namely the design admittances y0, y'0 of the two hybrids. Such an inverter, when terminated at its output port by a load admittance y, will give at its input port an input admittance yin = y0y'0/y.

Expressions are derived for the y parameters of the inverter at higher frequencies, thus accounting for the finite bandwidth of the op‐amp.

Two special cases are particularly treated, and experimental results are obtained for them. The first is the case of the resistive gyrator, for which y0 and y'0 are pure conductances. The second is the case of the capacitive gyrator, for which y0 and y'0 are pure capacitive susceptances. The capacitive gyrator is used to produce the supercapacitor, or f.d.n.r., and the results of measurements on a number of f.d.n.r. networks are given.
Double predistortion for electrical filters
Authors: Beccari C.
Published: July 2007

When dealing with filters with very stringent specifications, even the best predistortion techniques fail, because they all deal only with the natural modes, on the assumption that the losses produce a performance degradation mainly in the passbands. A new technique is proposed that is shown to be also effective with stringent specifications.
Canonic realization of wave digital filters involving unit elements
Authors: Meerkötter K.
Published: July 2007

Recently, a method has been developed by means of which canonic wave digital filters can be derived from originally noncanonic ladder wave digital filters. This method applies only to wave digital filters which are derived from pure LC‐ladder reference filters. In the paper, it is shown how noncanonic wave digital filters corresponding to reference filters containing unit elements can be transformed such that a canonic realization of these filters can be obtained as well.
On the efficient wave digital filter realization using programmable hardware
Authors: Nouta R.
Published: July 2007

A method is indicated by which wave digital filters of the true ladder structure can be realized efficiently using programmable hardware consisting of the following parts: arithmetic memory, program memory, coefficient memory and arithmetic unit.

It is shown how to minimize the complexity of the first two mentioned memories.
Some topologico‐dynamical properties of linear passive reciprocal networks
Authors: Milić M. M.
Published: July 2007

The paper considers the complete solvability and the order of complexity of passive RLCT (T = multiwinding ideal transformer) networks. A topological approach based on the determinant polynomial of the matrix of hybrid equations, formed as a set of 1st‐order differential and algebraic equations, reveals the structure of the formulation tree and the subnetworks accountable for degeneracies. Topological and algebraic degeneracies are defined. Necessary and sufficient conditions for complete solvability are derived, and two algorithms are given to determine the order of complexity topologically, i.e. without having an explicit state‐space representation.
An efficient method for obtaining element values of ladder filters whose transfer functions possess complex zeros and whose reactive components have freely assignable losses
Authors: Nightingale C.
Published: July 2007

An efficient method for designing doubly terminated ladder filters in which reactive components have freely assignable losses is described. The method uses partial knowledge of the driving‐point impedance of such filters to generate a set of algebraic equations which are easily solved using a computer program. An example of the application of the method to the design of an active filter is included.
Application of brune's tests to a class of network interconnections
Authors: Zelyakh E. W.
Published: July 2007

In most cases, checking the regularity of an interconnection of 4‐terminal networks with the aid of Brune's tests represents no difficulties. However, there is a class of interconnections for which Brune's procedure is not clear, and requires more subtle consideration. The method of application of Brune's tests to such interconnections is shown. The formulae determining the matrices of some regular interconnections of the said class are also given.
Critical block analysis for the transfer, gain and phase functions in multiple‐loop feedback networks
Authors: Acar C. , Ghausi M. S. , Laker K. R.
Published: July 2007

Measures for determining the most and least critical blocks in multiple‐loop feedback networks are defined for the transfer, gain and phase functions. Simple and systematic procedures for computing their values, thus determining the ordered hierarchy of critical blocks, are provided. The knowledge of the most and least critical blocks is shown to provide useful guidance for modifying component tolerances to produce higher yield or lower component costs. The tolerance assignment procedure described differs from those described elsewhere in that multiple component tolerances are assigned simultaneously on a block‐by‐block basis.
On a generalization of the wave digital filter concept
Authors: Lawson Stuart S.
Published: July 2007

The design of digital filter structures imitating the behaviour of classical analogue networks has received considerable interest in the literature. Of particular interest has been the Wave Digital Filter first considered by Fettweis. We examine here a generalization in which the relationships between the voltages, currents and wave variables are considered as a linear transformation on the ABCD matrix of the analogue two‐port network. The linear transformation is examined in some detail and conditions are derived which impose constraints on the elements of the matrices involved in the transformation. Finally a table giving thirteen transformations known to yield realizable digital filter structures is presented.
Amplifier nonlinearities in the multiple‐negative‐feedback bandpass filter
Authors: Bowron P. , Mohamed M. A.
Published: July 2007

A unified treatment is presented of the effect of both linear and nonlinear imperfections in an operational amplifier on the frequency response of a bandpass multiple‐negative‐feedback active filter. Linear computer models and describing‐function techniques are used to evaluate performance for comparison with measurements. The critical peak‐input voltage to avoid jump resonance is derived and performance limits illustrated on a Q–frequency plane.
A note on high‐Q active networks
Authors: Tow James , Gadenz Renato N.
Published: July 2007

Levi's and Zeheb's approach for approximating a high‐Q second‐order section by n sections with lower Q's is compared with the optimal solution of this problem proposed by Khazanov. Tables relating the maximum error in the approximation to the values of n and the achievable Q‐reduction (QR) are also given. They should prove useful to the designer. Finally, some comments on sensitivities are added.
A universal active R biquad
Authors: Soliman Ahmed M. , Fawzy Mahmoud
Published: July 2007

A universal active R biquad structure is presented which uses only resistors and two operational amplifiers. The network provides general biquadratic, band‐pass and low‐pass characteristics and is suitable for high‐frequency applications at medium pole Q values. When the network is adjusted to realize a high‐pass characteristic it becomes a special case from Schaumann's circuit N. The biquad circuit is recommended for monolithic integration.
Roundoff noise properties of second‐order digital notch filters
Authors: Roy S. C. Dutta , Patney R. K.
Published: July 2007

With regard to their roundoff noise properties, canonical second‐order recursive digital notch filters, with zeros on the unit circle and poles near them, are shown to fall in three distinct groups depending upon the zeros of their noise transfer functions (NTF's).

One of the groups, having all‐pole NTF'S, shows large noise magnitudes but the noise behaviour is well defined. The second group shows low noise magnitudes that heavily depend upon the location of the zeros of their NTF's; these zeros are related to the transfer function coefficients in a particularly simple manner. When this dependence gets complicated, as for the third group, the noise properties are ill behaved.
Tolerance optimization using stochastic programming
Authors: Hamza M. H. , Salama A. I. A.
Published: July 2007

Stochastic programming is used to determine the tolerances of components of electrical networks so as to minimize the total costs of the networks. The tolerances are assumed to have probability distributions around nominal values. Sensitivity functions are employed. An illustrative example is given.