Library

X
Your search history is empty.
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Übergangsmetallaktivierte organische Verbindungen, XXXVII. über eine neue Aldehyd-und Ketonreaktion: Synthese und spektroskopische Untersuchung von α1-Phosphonioalkoxy-übergangsmetallkomplexenHerrn Professor Ulrich Schöllkopf zum 65. Geburtstag gewidmet. (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 453-457 
    Details
    ISSN: 0009-2940
    Keywords: Aldehydes ; Ketones ; Titanium complexes ; Niobium complexes ; Tantalum complexes ; Phosphonium chlorides ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transition Metal-Activated Organic Compounds, XXXVII[1].  -  A Novel Reaction of Aldehydes and Ketones: Synthesis and Spectroscopic Investigation of α1-Phosphonioalkoxy Transition Metal ComplexesHerrn Professor Ulrich Schöllkopf zum 65. Geburtstag gewidmet.By treatment of aldehydes and ketones with one mole equivalent of a Lewis acid (TiCl4, NbCl5, TaCl5) and one mole equivalent of PPh3, or in one case of Ph2PCH2CH2PPh2, the aldehyde derivates [R1CH(P+Ph2R2)-OMCln]Cl- (4-8; M=Ti, Nb, Ta; R2=Ph or CH2CH2PPh2) and the ketone derivatives [R1R2C(P+Ph3)-ONbCl4]Cl- (9-10) were prepared. Complexes 4-10 were isolated as air-and water-sensitive solids. According to the NMR spectra some of the obtained aldehyde derivatives 4-8 exist in solution as a mixture of isomers or oligomers, whereas the ketone derivatives 9 and 10 form in solution an equilibrium with the free ketone and the complex NbCl5 · PPh3. The chloride ion of 4-10 is perhaps coordinated to the metal.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260224
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Übergangsmetallaktivierte organische Verbindungen, XXXVIII. Chemoselektive nucleophile Methylierungen durch In-Situ-Blockierung von Aldehydgruppen unter α1-Phosphonioalkoxid-BildungHerrn Professor Ulrich Schöllkopf zum 65. Geburtstag gewidmet. (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 459-464 
    Details
    ISSN: 0009-2940
    Keywords: Chemoselectivity ; Titanium complexes ; Niobium complexes ; Tantalum complexes ; Methylation of aldehydes and ketones ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transition Metal-Activated Organic Compounds, XXXVIII[1].  -  Chemoselective Nucleophilic Methylation Reactions by In-Situ-Blocking of Aldehyde Groups by α1-Phosphonioalkoxide FormationHerrn Professor Ulrich Schöllkopf zum 65. Geburtstag gewidmet.For the selective methylation of a keto group in the presence of an aldehyde group the complex MeTiCl3·PPh3 and especially the reagent system [TiC]4·PPh3 + 0.5 Me2Zn] proved to be favourable. For instance, 6-oxoheptanal (8) was methylated by [TiCl4·PPh3 + 0.5 Me2Zn] at the keto group with 89% yield and 99:1 selectivity, whereas it was methylated by [TiCl4 + 0.5 Me2Zn] at the aldehyde group with 81% yield and 96:4 selectivity. A selective methylation of benzaldehyde in the presence of heptanal was achieved with MeNbCl4·PPh3 or [NbCl5·PPh3 + 0.75 Me2Zn] to give (1-chloroethyl)benzene (14; yield 92 or 53%; selectivity in each case 93:7) or with [TaCl5·PPh3 + 1.5 Me2Zn] to give mainly 1-phenylethanol (15) besides 16. A 96:4-selective benzylation (yield 74%) of a ketone in the presence of an aliphatic aldehyde was possible with [TiCl4·PPh3 + 1 PhCH2MgBr].  -  The high chemoselectivity is caused by irreversible blocking of aliphatic aldehyde groups by α1-phosphonioalkoxide formation[1], whilst the corresponding reaction of keto groups[1] and of benzaldehyde is reversible.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260225
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Novel Reactions of Organomolybdenum and Organotungsten Compounds: Additive-Reductive Carbonyl Dimerization, Spontaneous Transformation of Methyl Ligands into μ-Methylene Ligands, and Selective CarbonylmethylenationOrganomolybdenum- and Organotungsten Reagents, Part 7. Part 6: [1]. (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 36 (1997), S. 1258-1275 
    Details
    ISSN: 0570-0833
    Keywords: C—C coupling ; carbonylmethylenation ; μ-methylene complexes ; molybdenum ; tungsten ; Carbonyl methylenation ; C-C coupling ; Bridging ligands ; Molybdenum ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hitherto there was no reaction known that permits transformations of R1R2-CO → 0.5 R1R2R3C-CR1R2R3 in one step. This type of additive-reductive carbonyl dimerization is now possible using alkoxy(alkyl)tungsten(v) complexes with aromatic, heteroaromatic or α,β-unsaturated aldehydes and ketones. When a corresponding phenyl complex was employed in a test experiment, it was revealed that an aliphatic ketone could be used as the substrate in this reaction. A second interesting type of reaction is the transformation of CH3 ligands into μ-CH2 ligands, which occurs during the treatment of MeLi or Me3Al with molybdenum or tungsten chlorides (oxidation states VI and V, for Mo additionally IV) at low temperatures with liberation of CH4. Here, the question arises as to whether the intermediate involved has a terminal CH2 ligand (Schrock carbene complex) or a μ-CH3 ligand (CH3 bound by a two-electron three-center bond to two metal atoms). Of all the μ-CH2 complexes obtained, those which were synthesized by the action of MeLi on molybdenum chlorides can be recommended as reagents for carbonylmethylenation of aldehydes and ketones. They display high selectivity, very low basicity, a surprising resistance to protons, they are readily available, can be easily modified and, as regards their selective behavior, they have been investigated more thoroughly than other readily accessible carbonylmethylenation reagents of comparable selectivity. The results of NMR spectroscopic investigations on the structure of the μ-CH2 complexes, and associated reaction mechanisms are discussed. A survey of carbonylmethylenation reagents, which have been reported in the literature, permits comparisons to be made with carbonylmethylenating molybdenum and tungsten complexes.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199712581
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Oxidative Coupling via Organocopper CompoundsProtophanes and Polyarenes, Part 13. Part 12: [94].Dedicated to Professor Heinrich Hellmann on the occasion of his 60th birthday (1974)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 13 (1974), S. 291-305 
    Details
    ISSN: 0570-0833
    Keywords: C-C coupling ; Organocopper compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The type of reaction described here, which achieved preparative importance before the turn of the century in the form of the Glaser reaction, has found new applications in recent years: Syntheses of 1,3-dienes, 2,3,6,7-tetraaza-1,3,5,7-tetraenes, 2,3-diaza-1,3-dienes, hydrazine derivatives, bis(heteroallyl) compounds, hetarenes, polyhetarenes, cyclopolyarenes, protophanes, phanes, and heteraprotophanes. The reaction, which consists in the metalation of the starting substance followed by oxidative coupling of the metal derivative, merits special preparative interest when several successive coupling processes are possible (e. g. polyyne, polyarene, cyclopolyarene, and protophane syntheses). The main factors limiting its applicability are the high thermal stability of some organic copper compounds and the disproportionation of the ligands that frequently occurs as a competing reaction. Selective asymmetric linkages are not generally possible by this method.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.197402911
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...