Homogeneity and Canonical Connections of Isoparametric Manifolds

On every isoparametric submanifold M a connection with parallel second fundamental form is constructed geometrically such that M is an orbit of an s-representation if and only if the connection is a canonical one. If the rank of M is greater than one this connection is in case of homogeneity the canonical connection of the reductive decomposition given by the orbit of s-representation. This revised version was published online in June 2006 with corrections to the Cover Date.     

MgF(3)(-) as a transition state analog of phosphoryl transfer

The formation of complexes between small G proteins and certain of their effectors can be facilitated by aluminum fluorides. Solution studies suggest that magnesium may be able to replace aluminum in such complexes. We have determined the crystal structure of RhoA.GDP bound to RhoGAP in the presence of Mg(2+) and F(-) but without Al(3+). The metallofluoride adopts a trigonal planar arrangement instead of the square planar structure of AlF(4)(-). We have confirmed that these crystals contain magnesium and not aluminum by proton-induced X-ray emission spectroscopy. The structure adopted by GDP.MgF(-) possesses the stereochemistry and approximate charge expected for the transition state. We suggest that MgF3(-) may be the reagent of choice for studying phosphoryl transfer reactions.     

Laccase-catalyzed carbon-carbon bond formation: oxidative dimerization of salicylic esters by air in aqueous solution

The laccase catalyzed oxidative dimerization of salicylic esters, a rare example of a laccase-catalyzed carbon-carbon bond formation, was studied. This reaction allows the use of air as stoichiometric oxidant and proceeds in aqueous solution. The preparative scope and the mechanism of the method, which provides a new and convenient access to functionalized biaryls under mild conditions, were investigated.     

Definitive Proof for the Operation of Isotopically Sensitive Branching (‘Metabolic Switching’) in FeI-Mediated C?H Bond Activation in the Gas Phase Short Communication

Rigorous regio- and stereospecific labeling experiments are performed to demonstrate the operation of the previously suggested operation of ‘isotopically sensitive branching’ in Fe^I-mediated C? H bond activation. For the hexane-1,6-diol/Fe⁺-complex, it is shown that dehydrogenation involves specifically the central C(3)/C(4) position, and the study of the stereospecifically labeled D ,L - and meso-[3,4-D₂]-isotompomers 1e and 1f demonstrates that dehydrogenation proceedes via two competing pathways (i.e. ‘anti’- vs. ‘syn’-route). The contribution of these routes to the product formation is – due to a kinetic isotope effect – controlled by the relative configuration at the labeled positions C(3)/C(4). For the D ,L -form 1e , we estimate a ratio of 49:1 in favor of the ‘anti’-route; due to an isotope effect, this ratio drops to 4.3:1 for the meso-form 1f .     

Chemistry of polyfunctional molecules-123. Reactions of BiBr3, SbI3 and AsI3 with LiN(PPh2)2; X-ray structure of a cyclophosphazene salt containing arsenic(I)

BiBr₃ or SbI₃ react at 20°C with LiN(PPh₂)₂ (1) to give elementary Bi or Sb and the P---P coupled phosphazene ligand Ph₂P---N=PPh₂---PPh₂=N---PPh₂ (2). The reaction of AsI₃ with 1 at room temperature formed yellow needles of the eight-membered heterocycle (3), whereas AsI₃ interacted at 80°C with 1 in the molar ratio of 1:3 to give elementary arsenic and 2. Treatment of AsI₃ and 1 at 20°C in a 1:2 stoichiometry yielded the seven-membered, cyclic arsenium(I) salt

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I·4THF (5·4THF), which was characterized by elemental analysis, conductivity, mass, IR and NMR spectroscopy and single-crystal X-ray structural analysis.     

Gas Phase Catalysis by Metal Nanoparticles in Nanoporous Alumina Membranes

Nanoporous alumina membranes, loaded with palladium and ruthenium nanoparticles of various size, were used for gas phase hydrogenation of 1, 3‐butadiene and for oxidation of carbon monoxide, respectively. Those membranes contain 10⁹ ‐ 10¹¹ pores per cm², all running perpendicular to the surface. Membrane discs of 20 mm in diameter and only 60 μm thick, incorporated in a reactor in which the reactants can be pumped in a closed circuit through the pores, turned out to very actively catalyze hydrogenation of butadiene (Pd) and oxidation of CO (Ru). The activity of the Pd catalysts depends characteristically on the particles size, the gas flow, and of the educts ratio. As could be expected, larger particles are less active than smaller ones, whereas increasing gas flows in case of hydrogenation accelerates the reactions. Excessive hydrogen reduces selectivity with respect to the various butenes, but favours formation of butane.     

Komplexchemie polyfunktioneller Liganden. XLV. Tetracarbonylchrom-, -molybdän- und -wolframkomplexe mit 1,1,1-Tris(diphenylarsinomethyl)ethan

Complex Chemistry of Polyfunctional Ligands. XLV. Tetracarbonylchromium, -molybdenum, and -tungsten Complexes of 1,1,1-Tris(diphenylarsinomethyl)ethan Ultraviolet irradiation of M(CO)₆ (M = Cr, Mo, W) with the potentially tridendate chelating ligand CH₃C[CH₃As(C₆H₅)₂]₃ react in CH₃CN to the complexes cis-M(CO)₄CH₃C[CH₂As-(C₆H₅)₂]₃ in which always one arsenic donor of the ligand is uncoordinated. The vibrational spectra (i.r., f.i.r., and Raman) of the compounds are discussed in detail.     

Chemie polyfunktioneller liganden LXIII. Adamantankäfigverbindungen mit den heteroelementen arsen,stickstoff und silizium

The reaction of 1,1,1-tris(diiodarsinomethyl)ethane, CH₃C(CH₂AsI₂)₃ (I), with i-C₃H₇NH₂, n-C₄H₉NH₂, C₆H₅NH₂, p-CH₃C₆H₄NH₂ and [(CH₃)₃Si]₂NH in the presence of (C₂H₅)₃N as auxiliary base in THF gives the adamantane cage compounds CH₃C(CH₂AsNC₃H₇)₃ (III), CH₃C(CH₂AsNC₄H₉)₃ (IV), CH₃C(CH₂AsNC₆H₅)₃ (V), CH₃C(CH₂AsNC₆H₄CH₃)₃ (VI) and CH₃C[CH₂AsNSi(CH₃)₃]₃ (VII). VII is also obtained in the reaction of I with NaN[Si(CH₃)₃]₂. The by-product (CH₃)₃SiO(CH₂)₄I (VIII) could be isolated in both syntheses of VII. All compounds have been characterized by mass spectrometry and infrared, Raman and ¹H NMR spectroscopy.     

Chemie polyfunktioneller Moleküle. 101 [1]: Synthese eines Diphenylphosphin-substituierten Cyclophosphamide und Röntgenstrukturanalyse seines Oxidations-produkts

Inhaltsübersicht. Diphenylphosphin und rac-Cyclophosphamid (ClCH₂CH₂)₂NP(O)N(H)(CH₂)₃O (1) reagieren in Gegenwart von n-Butyllithium zu einem Zwischenprodukt, das mit Wasser das diphenylphosphinsubstituierte Cyclophosphamid, (Ph₂PCH₂CH₂)₂NP(O)N(H)(CH₂)₃O, (2) bildet. Metallierung von 2 mit n-BuLi am N(3)-Atom und Umsetzung mit D₂O führt zum N(3)-Deuteroderivat 2a. Mit H₂O₂ reagiert 2 zur all-Phosphinoxid Verbindung, [Ph₂P(O)CH₂CH₂]₂NP(O)N(H)(CH₂)₃O, (4), die mit 0,5 Mol Wasser auskristallisiert und von der zur Charakterisierung des H-Bückenbindungssystems eine Röntgenstrukturanalyse angefertigt wurde. Die NMR-Spektren (¹H, ¹³C, ³¹P, ¹⁴N) weisen 2–4 als dynamische Moleküle aus. Chemistry of Polyfunctional Molecules. 101. Synthesis of a Diphenylphosphinesubstituted Cyclophosphamide and the X-ray Diffraction of its Oxidation Product Diphenylphosphine and rac-cyclophosphamide, (ClCH₂CH₂)₂NP(O)N(H)(CH₂)₃O, (1) react in the presence of n-BuLi to an intermediate which hydrolyses to the diphenylphosphine substituted Cyclophosphamide, (Ph₂PCH₃CH₂)₂NP(O)N(H)(CH₂)₃O, (2). Metallation of 2 with n-BuLi at the N(3) atom, followed by treatment with D₂O yields the N(3)-deuterated derivative 2a. With H₂O₂ 2 forms the all-phosphine-oxide compound, [Ph₂P(O)CH₂CH₂]₂NP(O)N(H)(CH₂)₃O, ( 4 ), which crystallizes with 0.5 mole of water. In order to characterize the H-bridge bonding system a X-ray structure analysis of 4 was carried out. The NMR-Spectra (¹H, ¹³C, ³¹P, ¹⁴N) indicate 2–4 as dynamic molecules.