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X-ray Crystal Structure Determination (x-ray + crystal_structure_determination)
Selected AbstractsSynthesis of Enantiopure Sulfonimidamides and Elucidation of Their Absolute Configuration by Comparison of Measured and Calculated CD Spectra and X-Ray Crystal Structure DeterminationCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2010Christin Worch Abstract Straightforward syntheses of enantiopure N -benzoyl- and N - tert -butyloxycarbonyl-protected sulfonimidamides, which can be used as building blocks in newly designed catalysts, are presented. Key synthetic step is a dynamic resolution of a racemic sulfinic acid sodium salt. All subsequent transformations proceed stereospecifically. The absolute configurations at the sulfur atoms of both sulfonimidamides were determined by comparison of measured and calculated CD spectra. An X-ray crystal structure determination of a sulfonimidoylguanidine derivative confirmed this result. [source] P-Chirogenic Benzo-Fused Phenoxaphosphane: Synthesis, Resolution and Study of the Stereochemical Properties of the Corresponding Palladium ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2008Franco Doro Abstract The synthesis and resolution of chiral phenoxaphosphane 3, with the stereogenic center at the phosphorus atom, is described. Compound 3 has been synthesized following a well-known procedure for trapping a phosphorus atom within a six-membered ring. The resolution of the racemic mixture of 3 was achieved through separation of its diastereomeric palladacycle derivatives 7a,b and 9a,b. The absolute configuration of enantiopure phosphanes 3a,b was assigned unequivocally by means of X-ray crystal structure determination for complex 9a and by combination of NOE(1H,1H)/COSY(1H,1H) spectroscopy and DFT calculations for complexes 7a,b, which in both cases led to identical results. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Diastereopure Cationic NCN-Pincer Palladium Complexes with Square Planar ,4 - N,C,N,O CoordinationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2006Silvia Gosiewska Abstract Neutral NCN-pincer palladium bromide complex 2 containing the monoanionic, enantiopure pincer ligand 2,6-bis{[(S)-2-hydroxymethyl-1-pyrrolidinyl]methyl}phenyl bromide (1) with bis- ortho -(S)-prolinol substituents was synthesized and isolated as a mixture of three stereoisomers [(SN,SN,SC,SC), (RN,SN,SC,SC), and (RN,RN,SC,SC)] in a 1:1:1 ratio. Upon abstraction of the bromide ion from the unresolved mixture of 2, single diastereoisomers of the cationic complexes [3]BF4 and [3]PF6, respectively, were formed with a unique,4 - N,C,N,O coordination mode of ligand 1. X-ray crystal structure determination established the intramolecular,4 - N,C,N,O coordination of 1 to palladium where the typical mer -,3 - N,C,N pincer coordination is accompanied by coordination of one of the hydroxy groups of the (S)-prolinol moieties. The water molecule that was cocrystallized in the crystal structure of [3]PF6 does not coordinate to palladium, but instead is involved in a hydrogen bonding network. The catalytic potential of both cationic complexes, [3]BF4 and [3]PF6, was tested in an aldol reaction of aldehydes with methyl isocyanoacetate to yield the oxazoline products as racemic mixtures.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] gem -Dimethylcyclopropanation of dibenzylideneacetone using triisopropyl sulfoxonium tetrafluoroborateACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Michael G. Edwards The reaction between dibenzylideneacetone (dba) and triisopropyl sulfoxonium tetrafluoroborate has been reinvestigated. The stereochemistry of the major diasteromeric bis(gem -dimethylcyclopropane) adduct has now been assigned as [(1RS,3RS)-2,2-dimethyl-3-phenylcyclopropyl][(1SR,3SR)-2,2-dimethyl-3-phenylcyclopropyl]methanone, C23H26O, by X-ray crystallographic studies on a twinned crystal. The asymmetric unit contains two molecules of the adduct, the conformations of which differ in the orientation of the phenyl ring relative to the adjacent cyclopropanated double bond. The carbonyl groups of each adduct are aligned approximately along the a axis and in opposite directions to each other. The molecules pack to give a sinusoidal pattern along the b axis. This is the first acyclic bis(dimethylcyclopropyl) ketone for which an X-ray crystal structure determination has been reported, and is also the first bis-cyclopropanated dba analogue. The knowledge that the major diastereomer has the meso structure (and therefore the confirmation that the minor isomer is the racemate) will prove invaluable in future studies to utilize bis(dimethylcyclopropyl) ketones as reagents, in rearrangement processes, and as potential ligands and ligand precursors in organometallic chemistry. [source] Asymmetric Hydrogenation with Highly Active IndolPhos,Rh Catalysts: Kinetics and Reaction MechanismCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2010Jeroen Wassenaar Abstract The mechanism of the IndolPhos,Rh-catalyzed asymmetric hydrogenation of prochiral olefins has been investigated by means of X-ray crystal structure determination, kinetic measurements, high-pressure NMR spectroscopy, and DFT calculations. The mechanistic study indicates that the reaction follows an unsaturate/dihydride mechanism according to Michaelis,Menten kinetics. A large value of KM (KM=5.01±0.16,M) is obtained, which indicates that the Rh,solvate complex is the catalyst resting state, which has been observed by high-pressure NMR spectroscopy. DFT calculations on the substrate,catalyst complexes, which are undetectable by experimental means, suggest that the major substrate,catalyst complex leads to the product. Such a mechanism is in accordance with previous studies on the mechanism of asymmetric hydrogenation reactions with C1 -symmetric heteroditopic and monodentate ligands. [source] Synthesis of Enantiopure Sulfonimidamides and Elucidation of Their Absolute Configuration by Comparison of Measured and Calculated CD Spectra and X-Ray Crystal Structure DeterminationCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2010Christin Worch Abstract Straightforward syntheses of enantiopure N -benzoyl- and N - tert -butyloxycarbonyl-protected sulfonimidamides, which can be used as building blocks in newly designed catalysts, are presented. Key synthetic step is a dynamic resolution of a racemic sulfinic acid sodium salt. All subsequent transformations proceed stereospecifically. The absolute configurations at the sulfur atoms of both sulfonimidamides were determined by comparison of measured and calculated CD spectra. An X-ray crystal structure determination of a sulfonimidoylguanidine derivative confirmed this result. [source] Structure determination of chiral sulfoxide in diastereomeric bicalutamide derivativesCHIRALITY, Issue 6 2009Wei Li Abstract We report on the synthesis and investigation of two diastereomers (5a and 5b) of a new bicalutamide analog with an asymmetric carbon atom and a chiral sulfoxide group. These bicalutamide analogs are novel androgen receptor antagonists with biological activities that depend significantly on the configuration of their stereogenic centers. We determined the absolute configuration at the SO center by combining X-ray and NMR measurements with quantum chemical calculations. Since 5a and 5b failed to yield satisfactory crystals for X-ray crystal structure determination, analogs 6a and 6b differing in only one remote functional group relative to the chiral sulfoxide were synthesized, which yielded satisfactory crystals. X-ray structure determination of 6a and 6b provided the absolute configuration at the chiral sulfoxide. Since the structural difference between 5 and 6 is remote from the chiral sulfoxide, the structural assignment was extended from the diastereomers of 6 to those of 5 provisionally. These assignments were verified with the help of measured and DFT-calculated proton and carbon NMR chemical shifts. Chirality, 2008. © 2009 Wiley-Liss, Inc. [source] | ||||||||||