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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis, Structure, and Reactivity of Chiral Rhenium Cycloalkene Complexes of the Formula ; Facile Vinylic Deprotonation of a Coordinated Alkene (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 729-742 
    Details
    ISSN: 0009-2940
    Keywords: Cycloalkene ligands ; Cyclopentylidene ligands ; Deprotonotion reactions ; Rhenium complexes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of [(η5-C5H5)Re(NO)(PPh3)(ClC6H5)]+BF-4 and (n = 5, a; 6, b; 7, c; 8, d) give cycloalkene complexes (6a - d, 94 to 79%). A crystal structure of the methylcyclopentadienyl analog of 6a shows the Re - plane and Re - PPh3 bond to be coplanar, with the vinyl protons syn to the cyclopentadienyl ligand. Reaction of 6a and tBuO-K+ leads to the vinyl complex (9a, 90%) instead of expected allyl complex (10a) Analogous reactions of 6b - d give varying mixtures of 9b - d/10b - d. HBF4 · OEt2 and 9a react to form the cyclopentylidene complex (10+ BF-4, 96%), the stability of which precludes any intermediacy in the deprotonation of 6a. A crystal structure of 11+ PF-6 shows the Re=C—C planes to be perpendicular to the Re - P bond. Spectroscopic features of compounds 6 are analyzed in detail, and NMR data show a high barrier to cyclopentylidene ligand rotation in 11+ BF-4 (ΔG≢ (110°C) ≥ 19 kcal/mol).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911240410
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  • 2
    Electronic Resource
    Electronic Resource
    Chiral Recognition in π Complexes of Alkenes, Aldehydes, and Ketones with Transition Metal Lewis Acids; Development of a General Model for Enantioface Binding Selectivities (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 36 (1997), S. 550-583 
    Details
    ISSN: 0570-0833
    Keywords: alkene complexes ; carbonyl complexes ; chiral recognition ; stereoselective syntheses ; transition metal Lewis acids ; Alkene ligands ; Carbonyl ligands ; Chiral recognition ; Stereoselectivity ; Lewis acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Prochiral alkenes, aldehydes, and ketones constitute the most frequently used starting materials for enantioselective organic syntheses. Protocols often involve chiral binding agents or Lewis acids that can give two diastereomeric adducts, the ratios of which are measures of chiral recognition. With π adducts, the diastereomers differ in the enantioface of the C=C or O=C group bound to the Lewis acid. This review provides the first comprehensive analysis of such equilibria and related binding phenomena with chiral transition metal Lewis acids. An extensive body of data from the authors' laboratory for complexes of the pyramidal rhenium fragment [(η5-C5H5)Re(No)(PPh3)]+ (I) affords particular insight. Literature data for other complexes are also summarized. A general model for chiral recognition based upon the relative steric properties of four quadrants is presented. This enables binding selectivities to be individually and rationally optimized for different classes of ligands. Electronic effects are also identified and correlated with specific structural properties. Relationships between binding equilibria, reactivity, and product configurations are discussed.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199705501
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    Paper (German National Licenses)
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