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Boron Atom (boron + atom)
Selected AbstractsInvestigations on 1-MetallaindanesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2003Marcel Schreuder Goedheijt Abstract 1-Mercuraindane (6) was prepared in three steps from 1-bromo-2-(2-bromoethyl)benzene (3) and converted into 1-magnesaindane (1) by reaction with magnesium. In solution, 6 was observed to occur in a remarkable dimer/trimer equilibrium, whereas 1 forms a dimer. From 1 and dichlorozirconocene, the 1-zirconaindane 2 was obtained, which reacted with B(C6F5)3 to form the adduct 13. According to spectroscopic data, 13 is formed by attack of the ,-methylene carbon atom at the boron atom and has a zwitterionic structure with weak interactions between the zirconium ion and one of the ortho -fluorine atoms. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Boron-Based Diastereomerism and Enantiomerism in Imine Complexes , Determination of the Absolute Configuration at Boron by CD SpectroscopyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 31 2008Manfred Braun Abstract Boron turns out to be a stable stereogenic center in imine complexes of aryl and alkyl boronates. Diastereomerically pure complexes 7a,c are obtained from chiral imine ligands 5a,b that are derived from the amino alcohol (R)- 4. The configuration at the boron atom is determined by crystal structure analyses. Racemic boronates 10a,c, available from a condensation of aryl boronic acids 6 with the achiral imine ligand 9, can be separated into stable enantiomers by HPLC on a chiral column. The racemization barrier ,G, has been determined to amount to 105,115 kJ,mol,1. The comparison of calculated and measured CD spectra permits to assign unambiguously the absolute configuration to boron in the enantiomeric boronate-imine complex 10a.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] On the binding mode of urease active site inhibitors: A density functional studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2008M. Leopoldini Abstract The way with which boric acid, a rapid reversible competitive inhibitor, binds the urease active site was explored at density functional B3LYP level of theory. The catalytic core of the enzyme was simulated by two models of different size. In both cases, amino acid residues belonging to the inner and to the outer coordination spheres of nickel ions were replaced by smaller molecular species. Contrary to the experimental indication that attributes the inhibitory ability of this acid to the lack of a nucleophilic attack by the enzyme to the boron atom, we instead found that another possibility exists based on the presence of a strong covalent , bond between boron and urease that we think can be hardly broken to allow any course of the reaction. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] ,-Amino boronates as cyanoborane complexes: crystal structure and inhibition properties for the serine proteases: ,-chymotrypsin and trypsinAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 7 2006Amal Shibli Abstract The first examples of ,-amino boronate complexes stabilized by amino cyanoborane complexation were tested as trypsin and chymotrypsin inhibitors, and they showed moderate inhibition. The structure of compound 1 that contains two different boron atoms reveals that the geometry around the boron atom in the cyano group is tetrahedral, whereas a trigonal planar geometry exists around the boron atom attached to two oxygen atoms and a carbon atom. Copyright © 2006 John Wiley & Sons, Ltd. [source] Dispersion-Oriented Soft Interaction in a Frustrated Lewis Pair and the Entropic Encouragement Effect in its FormationCHEMISTRY - A EUROPEAN JOURNAL, Issue 48 2009Woo Kim Abstract The origin of the stability of a frustrated Lewis pair (FLP) tBu3P:B(C6F5)3 is investigated computationally to demonstrate the importance of the dispersion interaction. To this end, the interaction between alkyl-substituted phosphines (Me3P and tBu3P) and hexafluorobenzene (C6F6) is first investigated. Driven by the lone-pair to ,-orbital interaction, the binding energy is found to be even larger than usual ,,, interaction energies between small aromatic compounds. This character, which is inherited to fluorophenyl-substituted B(C6F5)3 in the FLP, induces large flexibility in the FLP over the molecular surface of B(C6F5)3. This soft interaction, in turn, causes an entropic stabilization of the FLP formation in comparison with classical Lewis pairs based on close and tight PB dative bonds. It also suggests a diverse nature of the FLP when it is involved in chemical reactions. Even with the cooperative participation of the perfluorophenyl groups, a detailed inspection of the FLP interaction potential energy surface indicates that the boron atom is still the major interaction site for the pair formation. This non-negligible direct PB interaction, which is related also to the soft nature of the borane frontier orbital, is further supported by substantial spatial overlap between the frontier orbitals on the phosphine/borane fragments and their interaction energy estimations. [source] Preparation of highly optically pure homochiral sulfide-containing alcohols via oxazaborolidine-catalyzed asymmetric borane reduction of ketonesCHIRALITY, Issue 6 2004Jiaxi Xu Abstract Highly optically pure homochiral 1-(4-alkylthiophenyl) alcohols were prepared efficiently and practically via the oxazaborolidine-catalyzed asymmetric borane reduction of prochiral ketones in toluene at 25°C. The coordination of the sulfur atom in the ketones to the boron atom in the catalyst and borane can be inhibited under these reduction conditions. Chirality 16:341,346, 2004. © 2004 Wiley-Liss, Inc. [source] Synthesis of highly luminescent organoboron polymers connected by bifunctional 8-aminoquinolate linkersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2010Yuichiro Tokoro Abstract New organoboron aminoquinolate-based polymers linked by ,-conjugated bridge were prepared by Sonogashira,Hagihara coupling of organoboron aminoquinolate-based bisiodo monomers bearing biphenyl or bithiophene moiety with 1,4-diethynylbenzene derivatives. Tetracoordination states of boron atoms in the obtained polymers were confirmed by 11B NMR spectroscopy, and they were also characterized by 1H NMR and IR spectroscopies and size-exclusion chromatography. Their optical properties were studied by UV,vis absorption and photoluminescence spectroscopies. In the region above 400 nm, the polymers prepared from 1,4-diethynyl-2,5-dioctyloxybenzene showed bathochromic shifts when compared with those prepared from 1.4-diethynyl-2-perfluorooctyl-5-trifluoromethylbenzene. The polymers with biphenyl moiety showed higher absolute fluorescence quantum yields (,F = 0.28 and 0.65), whereas those with bithiophene moiety led to decreasing of the low quantum yields (,F = 0.19 and 0.00). The density-functional theory (DFT) and time-dependent,DFT calculations of model compounds corresponding to the polymers were in good agreement with the results from UV,vis properties. The calculations revealed that the electronic structure of the polymer with bithiophene moiety is different from that with biphenyl moiety, and predicted the electron transfer from the bithiophene moiety to the ,-extended quinoline moiety in transition state. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3693,3701, 2010 [source] Synthesis and molecular structure of 2,4,6-tri[bis(diisopropylamino)boryl(methylamino)]borazine, [(NiPr2)2B(Me)N]3B3N3H3APPLIED ORGANOMETALLIC CHEMISTRY, Issue 1 2003Bérangère Toury Abstract Reaction of bis(diisopropylamino)(methylamino)borane, (NHiPr)2B(NHMe), with 2,4,6-trichloroborazine (ClBNH)3 affords 2,4,6-tri[bis(diisopropylamino)boryl(methylamino)]borazine, 2,4,6-[(NiPr2)2B(Me)N]3B3N3H3, which is the first boryl-borazine structurally characterized. According to the X-ray single crystal structure and the chemical shifts of 11B NMR resonances of boron atoms, compared with the aminoborane and borazine analogs, the borazine and boryl ,-systems are not coplanar either in the solid state or in organic solution. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||