Asymmetrische Synthesen mit homogenen Übergangsmetallkatalysatoren

Abstract

Zum Gedenken an Kml ZieglerDer Fortschritt auf dem Gebiet der homogenen Katalyse in den letzten funf bis sechs Jahren ist gekennzeichnet u. a. durch die Entwicklung hochselektiver Katalysatoren fur asymmetrische Synthesen. Mit wohldefinierten ubergangsmetallkatalysatoren lassen sich bei asymmetrischen Hydrierungen in hornogener Phase optische Ausbeuten von 85 bis uber 90% erzielen. Bei katalytischen Reaktionen, bei denen die chiralen Zentren i m Zuge von C-C-Verknupfungen entstehen, wurden optische Ausbeuten von 70 bis 80 % erreicht.Als Katalysatoren fur die Hydrierungen dienen vornehmlich Rhodium(1)-Komplexe rnit ,,Homer-Phosphanen", Phosphanen mit chiralen C-Atomen oder optisch aktiven Amiden. Fur die C-C-Verkniipfungen unter Induktion optischer Aktivitat haben sich Katalysatoren bewahrt, die aus n-Allylnickelhalogeniden, Lewis-Sauren und Phosphanen rnit chiralen C-Atomen gewonnen werden. Die Ergebnisse bedeuten einen Durchbruch auf einem Katalysegebiet, das bisher Enzymen vorbehalten war.

η3‐Allylnickel alkoxides and their use as homogeneous and heterogeneous catalysts for the dimerization of olefins

“…1[BEt3H] in toluene (Eqn [3]) and then exchanged with 1 (X = Br) in CH2C12 or toluene (Eqn [4]). The suspended heterogeneous catalyst precursor, e.g.…”

“…Alumina (Condea), silica (Merck), Bayerit (Degussa) and rutile (Bayer) wcre dried in two steps and the free-surface OH-groups available as anchoring groups on the dehydrated surfaces were quantitatively determined by volumetric measurement on the evolution of hydrogen on the reaction of the dry support materials with Na[BEt,H] in toluene (see Eqn [3] and Table 1). …”

Transition‐Metal‐Catalyzed Laboratory‐Scale Carbon–Carbon Bond‐Forming Reactions of Ethylene

“…The following year, Wilke reported the hydrovinylation of norbornadiene using 3.5 mol% of the allylnickel dimer and a slightly bulkier chiral phosphine at −65 °C. [27] In this instance, the hydrovinylation product (5 R )- 33 was formed in 49% yield with 78% enantiomeric excess ( ee ). The E - and Z -ethylidene derivatives 34 were also formed in 13% yield, and ethylene oligomerization products, likely arising from β-hydride elimination after ethylene migratory insertion, [25,28] were also observed.…”

New Functionalized Vinyl Monomers by Ethylene‐(Functionalized)‐Norbornene Hetero‐Trimerization Catalyzed by Cobalt(II)‐(Imino)pyridine Complexes

“…[8] One of the very first examples of this reaction was reported by Wilke who accomplished the highly stereoselective E/NB heterodimerization using p-allylnickel catalysts stabilized by optically pure phosphine ligands. [9] More recently, RajanBabu reported an effective way of tuning the selectivity of the 1E-1NB coupling by varying the phosphine that reacts with the p-allylnickel precursor (Scheme 2). [10] A much more challenging task is the catalytic synthesis of vinylnorbornanes bearing polar groups (hydroxy or carboxylic acid, for instance) that are generally incompatible with oxophilic catalysts as well as the most common activators of metal complexes.…”