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  • 1
    ISSN: 1434-1948
    Keywords: Carbon dioxide fixation ; Magnesium ; N ligands ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of oxalic amidines R1-N=C(NHR2)-C(NHR2)=N-R1 with CH3MgX followed by uptake of CO2 results in the formation of the trimeric carbamato complexes [R1-N=C(NR2-COO)-C(NR2COO)=N-R1]3Mg3(THF)6 (2a: R1 = R2 = Ph; 2b: R1 = R2 = p-tolyl) as the thermodynamically stable final products of the reaction. Their X-ray crystal structures show that the three metal centres are in a linear arrangement. The central magnesium ion is octahedrally surrounded by six O-donor atoms of the μ2-carbamato bridges, while both peripheral magnesium ions are facially coordinated by three O-donor atoms of the carbamato groups and three THF molecules. This coordination sphere can be considered as a structural model for the active centre in the ribulose-1,5-bisphosphate carboxylase/oxygenase enzyme. Compound 2a reacts with ZnCl2 or CoBr2, with CO2 elimination, to form dimeric complexes of the type [X2M(oxalamidinato)MX2][Mg(DMF)6] (M = Zn, Co; X = Cl, Br). X-ray crystal structure analyses show that the d-metals are tetrahedrally coordinated. The magnesium-bromide-containing intermediates in the formation of 2a and 2b are able to transfer CO2 to acetophenone, thus simulating the CO2 activation step in enzymatic biotin-dependent carboxylation reactions.
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  • 2
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 5-Ring-Cycloamidines - Deeply Coloured Heterocycles with Unusual Properties. I. Synthesis and Spectral FeaturesThe cycloacylation reaction of benzamidines with bis-imidoylchlorides 1 derived from oxalic acid was investigated. For example, treatment of benzamidine with 1 gives the new 4H-imidazoles (3a-l) in yields up to 92%. Because of rapid H-transfer processes in solution, the NMR-spectra of 3a-l show only a single signal set. Apart from prototropism, 3c shows interesting properties as an amphoteric heterocycle. The protonation of 3c is accompanied by a change of color from orange to blue. Probably, protonation takes place on the exocyclic imino nitrogen to give a cyanine type chromophor. The resulting cation can also be regarded as an antiaromatic 1,3-diazacyclopentadienylium system. In order to investigate the influence of exocyclic substituents at nitrogen on the UV/VIS absorption, compounds 3d-h were synthesized. Whereas electron withdrawing groups cause hypsochromic shifts of the first UV/VIS absorption band, the dimethylamino group shifts this band bathochromically as exemplified by 3e. This novel cycloamidine shows strong acidochromism with bathochromic shifts of more than Δλmax = 150 nm.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 337 (1995), S. 143-152 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Aminolysis of Bis-Imidoylchlorides of Oxalic Acid. Part I. Reaction with Aromatic and Aliphatic AminesThe reaction between bis-imidoylchlorides 2 derived from oxalic acid and several aromatic and aliphatic amines was investigated. While primary aromatic amines need a thermical activation by refluxing, primary aliphatic amines give mainly at room temperature the amidines 3 in moderatly up to good yields.Proceeding from enantiomeric pure amines e.g. (R)- or (S)-1-phenethylamine the new homochiral oxalic amidines 3y and 3z with C2-symmetry were obtained. Several secondary amines react with the bis-imidoylchloride 2a to give via intramolecular cycloacylation derivatives of isatine. The new synthesized amidines 3 perform systems with a strong molecular dynamic like prototropie and E/Z-interconversion. All new compounds described were characterized by elemental analysis and spectroscopic methods.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 339 (1997), S. 735-741 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 5-Ring-Cycloamidines - Deeply Colored Heterocycles with Unusual Properties. II. Molecular- and Electronic StructureThe crystal and molecular structure of two N,N′-aryl-5-amino-imidazole-4-imides were detected by X-ray analysis. The structural parameters are discussed in conjunction with theoretical data obtained by density functional and ab initio quantum theory. The interpretation of the molecular structures derived from the X-ray diffraction study is made more difficult by statistic disorder or by enclosure of water in the crystal. The theory predicts a planar 5-amino-imidazole-4-imide parent structure with an energy barrier to H-transfer of about 25 kcal/mol (DFT RB3LYP/6-311+G** and ab initio G2(MP2) calculations). The CC bond of the five-membered ring is exceedingly long. CC-bond length elongation is also reported for oxalbisamidine. The structure of the parent compound is discussed in terms of polymethinic and antiaromatic substructures. Weinholds's Natural Bond Orbital (NBO) scheme and Natural Resonance Theory (NRT) as well as Schleyer's criterion of the Nucleus Independent Chemical Shift (NICS) is consulted to reveal the very nature of the unique bond system.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 199-201 
    ISSN: 0947-3440
    Keywords: Macrocyclic lactams ; Oxalamides ; Atropisomeric diamines ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An Unexpected Reaction between Oxalyl Chloride and Atropisomeric DiaminesChiral diamines like (S)-1,1′-binaphthalene-2,2′-diamine (3a) were acylated by oxalyl chloride to yield mainly a macrocyclic lactame 5, whereas the eight-membered oxamide 4 was formed only in small quantity.
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  • 6
    ISSN: 0947-6539
    Keywords: carbon dioxide activation ; homogeneous catalysis ; ligand effects ; molecular modeling ; rhodium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexes [(P2)Rh(hfacac)] 1 [P2 = R2P-(X)-PR2] are introduced as model compounds for the investigation of the intrinsic steric properties of the [(P2)Rh] fragment. The ligand exchange processes that occur during the syntheses of 1 from [(cod)Rh(hfacac)] and the appropriate chelating diphosphanes 3 were studied by variable-temperature multinuclear NMR spectroscopy. The molecular structures of eight examples of 1 with systematic structural variations in 3 were determined by X-ray crystallography. The steric repulsion of the PR2 groups within the chelating fragment was found to significantly influence the coordination geometry of [(P2)Rh], depending on the nature and length of the backbone (X). A linear correlation between the P-Rh-P angles in the solid state and the 103Rh chemical shifts reveals a similar geometric situation in solution. A unique molecular modeling approach was developed to define the accessible molecular surface (AMS) of the rhodium center within the flexible [(P2)Rh] fragment. The potential of this model for application in homogeneous catalysis was exemplified by the use of 1 as catalysts in a test reaction, the hydrogenation of CO2 to formic acid. Complexes 1 were found to be the most active catalyst precursors for this process in organic solvents known to date.
    Additional Material: 9 Ill.
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  • 7
    ISSN: 0044-8249
    Keywords: Cyclopentadienyl-Analoga ; Heterodienkomplexe ; Komplexe mit Stickstoffliganden ; Lanthanoidverbindungen ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 8
    ISSN: 0044-2313
    Keywords: Zirconium ; Lithium ; Hydroxoligands ; Oxoligand ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: An Unusual Trimeric Bimetallic Li—Zr Complex with the Backbone [Zr3(μ2-OH)3(μ3-O)Li5] by Reaction of Zirconiumorgano and Hydrido Complexes with WaterThe reaction of compounds of the type [(LZr)(LiH)(L′)]n and [(LZr)(LiH)(L′)(alkyne)]n (L: 2,2′-Biphenolato-dianion, L′: thf, Bu3P, alkyne: Ph—C≡C—SiMe3, CH≡CH) with water at 0°C in a thf solution results in the formation of th trimeric bimetallic complex 8 [(L2Zr)3(μ2-OH)3(μ3-O)Li5(thf)8(H2O)5] in 50% yield. The X-ray analysis of 8 shows that a planar six-membered ring Zr3(μ2-OH)3 is formed. In the middle of this ring is a dianionic oxygen atom placed, coordinating to the three L2Zr centres in a planar μ3-coordination (bond angles 120,05μ). Five lithium ions stabilize the anionic backbone by bridging the biphenolato chelate ligands, which form seven-membered chelate rings with the atoms.1H-, 13C-, and 7Li-NMR spectra exhibit that the solid state structure remains unchanged in solution (thf).
    Notes: Die Reaktion von Verbindungen des Typs [(LZr)(LiH)(L′)]n und [(LZr)(LiH)(L′)(alkin)]n (L: 2,2′-Biphenolato-dianion, L′: thf, Bu3P, alkin: Ph—C≡C—SiMe3, CH≡CH) mit Wasser führt bei 0°C in thf in 50% Ausbeute zum trimeren Bimetallkomplex 8 [(L2Zr)3(μ2-OH)3(μ3-O) Li5(thf)8(H2O)5]. Die Kristallstrukturanalyse von 8 zeigt, daß ein planarer Zr3(μ2-OH)3-Sechsring gebildet wird. In seiner Mitte ist ein dianionisches Sauerstoffatom fixiert, das an den drei L2Zr-Zentren mit planarer μ3-Koordination gebunden ist (Bindungswinkel Zr—O—Zr 120,05°). Fünf Lithiumionen stabilisieren das anionische Gerüst durch Verbrückung der Biphenolatchelatliganden, die mit den Zr-Atomen Chelatsiebenringe ausbilden. 1H-, 13C- und 7Li-NMR-Spektren zeigen, daß in Lösung (thf) die Festkörperstruktur unverändert erhalten bleibt.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 623 (1997), S. 1135-1143 
    ISSN: 0044-2313
    Keywords: Copper(I) ; 1-azadienes ; oxidation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Copper(I) Complexes with 1-Azadiene Chelate Ligands and Their Reaction with OxygenThe reaction of the bidendate 1-azadiene ligands Me2N—(CH2)n—N=CH—CH=CH—Ph with CuX results in the formation of the dimeric compounds [ACuX]2 and [BCuX]2 (A: n = 2, B: n = 3, X: I, Cl). The structure of complex 1 [ACuI]2 was determined by X-ray crystal structure analysis. 1 consists of two tetrahedrally coordinated Cu atoms connected by two iodo bridges. (Cu—Cu bond length: 261 pm).The ligand Me—N(CH2CH2N=CH—CH=CH—Ph)2 (C) reacts with CuX to form the monomeric complexes [CCuX] (5: X=I, 6: X=Cl). The crystal structure of 5 shows that the ligand acts as a tridendate ligand. The bond lengths of the CuN(sp2) bonds are significantly shorter than the Cu—N(sp3) distance.Reacting the podand-type ligands N(CH2CH2—N=CH—R)3 (D: R=Ph, E: R=-CH=CH—Ph) with CuX yields the ionic complexes 7 [DCu][CuCl2] and 8 [ECu][CuCl2]. 7 was characterized by X-ray analysis which confirmed that D acts as a four-dendate podand ligand.The compounds 1-8 are unreactive towards CO2 but take up O2 even at deep temperatures. At -78°C the orange-red complex 4 [BCuCl]2 reacts with O2 in CH2Cl2 to form a deep violet solution, but the primary product of the oxidation could not be isolated. It reacts at room temperature to form the green complex 9 [μ-Cl, μ-OH][BCuCl]2. The X-ray structure analysis of 9 confirms that a dimeric CuII complex is formed in which both a chloro- and a hydroxo group are bridging the monomeric units. The CuII centers exhibit a distorted tetragonal-pyramidal coordination.The pathway of the reaction with O2 will be discussed.
    Notes: Die Reaktion der zweizähligen 1-Azadienliganden Me2N—(CH2)n—N=CH—CH=CH—Ph mit CuX führt zu den dimeren Komplexen [ACuX]2 and [BCuX]2 (A: n = 2, B: n = 3, X: I, Cl). Die Struktur des Komplexes 1 [ACuI]2 wurde durch Kristallstrukturanalyse bestimmt. 1 enthält zwei tetraedrisch koordinierte Cu-Atome, die über zwei Iodobrücken miteinander verknüpft sind Cu—Cu-Bindungslänge: (261 pm).Der Ligand Me—N(CH2CH2N=CH—CH=CH—Ph)2 (C) reagiert mit CuX unter Bildung der monomeren Komplexe [CCuX] (5: X = I, 6: X=Cl). Die Kristallstruktur von 5 zeigt, daß der Ligand dreizählig koordiniert. Die Bindungslängen der Cu—N(sp2)-Bindungen sind signifikant kleiner als der Cu—N-(sp3)-Abstand.Die Reaktion der Podand-Liganden N(CH2CH2—N=CH—R)3 (D: R=Ph, E: R=-CH=CH—Ph) mit CuX führt zu den ionischen Komplexen 7 [DCu][CuCl2] bzw. 8 [ECu][CuCl2]. 7 wurde durch Röntgenstrukturanalyse charakterisiert, die ausweist, daß D als vierzähliger Ligand fungiert.Die Komplexe 1-8 sind gegenüber CO2 nicht reaktiv, nehmen aber O2 schon bei tiefen Temperaturen auf. Bei -78°C reagiert der orangerote Komplex 4 [BCuCl]2 mit O2 in CH2Cl2 zu einer tiefvioletten Lösung, das Primärprodukt der Oxidation konnte jedoch nicht isoliert werden. Es reagiert bei Raumtemperatur zu dem grünen Komplex 9 [μ-Cl, μ-OH][BCuCl]2. Die Kristallstrukturanalyse belegt, daß ein dimerer CuII-Komplex gebildet wird, in dem eine Chloro- und eine Hydroxobrücke die Monomereinheiten verbrücken. Die CuII-Zentren weisen eine verzerrt tetragonal-pyramidale Koordination auf.Der Reaktionsweg der Umsetzung mit O2 wird diskutiert.
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  • 10
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 1133-1142 
    ISSN: 0887-624X
    Keywords: Diels-Alder polyaddition ; coronand structure ; bispyrones ; bismaleimides ; polyimides ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of various substituted bis(2-pyrone)s with bismaleimides in dilute solution was carried out to produce linear soluble polymers with coronand structure. The number-average molecular weights of the polymers ranged from 7000 to 18,000 (vapor pressure osmometry). Polymer structures were identified by NMR spectroscopy and model reactions. The stereochemistry and the mechanism are discussed. © 1995 John Wiley & Sons, Inc.
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