Strukturell definierte Allylverbindungen der Hauptgruppenmetalle: Koordination und Reaktivität

Characterization of Highly Coordinated Allylgermanes: Pivotal Players for Enhanced Nucleophilicity and Stereoselectivity

Allylgermanes with a 4-, 5-, and 6-coordinated germanium center were characterized by X-ray crystallography. Cationic 6-coordinated group 14 allylmetals, which were hitherto assumed to be a transition-state structure of allylations, were successfully isolated. Forming high coordination states significantly enhanced the reactivity of the allylgermanes. In contrast to the 4-coordinated allylgermanes with low reactivity, the highly coordinated species readily reacted with several aldehydes. Furthermore, the high coordination states exerted a significant effect on the E/Z selectivity of allylation depending on external additives. The coordination structure had a dramatic influence on the electronic and steric environments around the Ge center, enabling the geometrically controlled allylation of aldehydes.

Controlling the Coordination Sphere of Alkyllithiums Results in Selective Reactions with Allylic Amines

Described herein is a selective way to control the reaction of allylic amines with metalorganic bases depending on the amine handle as well as the metalorganic base is used. Depending on the number of coordinating groups within the amine handle either a selective carbometalation or deprotonation reaction can be performed. By changing the alkali metal within the base from lithium to either sodium or potassium, a change of chemoselectivity takes place and the reaction of piperidinoallylamine can be controlled.

Alkynes as Electrophilic or Nucleophilic Allylmetal Precursors in Transition-Metal Catalysis

Diverse late transition metal catalysts convert terminal or internal alkynes into transient allylmetal species that display electrophilic or nucleophilic properties. Whereas classical methods for the generation of allylmetal species often form stoichiometric by-products, the recent use of alkynes as allylmetal precursors enables completely atom-efficient catalytic processes to be carried out, including enantioselective transformations.

η(3) -Allyl coordination at tin(II)-reactivity towards alkynes and benzonitrile

We herein report the synthesis and characterization of a terphenyl-substituted Sn(II) allyl compound featuring an η(3)  coordination mode in solution and in the solid state. Two examples for the interesting reactivity of the allyl Sn(II) molecule are presented: Reactions with terminal alkynes result in the formation of tricyclic compounds by CC bond formation and the dimerization of two Sn moieties whereas the reaction with benzonitrile leads to a sixteen-membered ring system through CH activation.