Treatment of cyclic anhydrides with stoichiometric amounts of nickel−neocuproine complex generates alkylcarboxylato−nickelalactones upon extrusion of CO. These metalacycles undergo cross-coupling with arylzinc reagents. The generated CO is sequestered in situ by a nickel−dppb complex. The overall sequence effects a secondary sp3(electrophile)−sp2(nucleophile) cross-coupling and allows for control of stereochemistry during the bond-forming event.

Decarbonylative cross-coupling of cyclic anhydrides: introducing stereochemistry at an sp3 carbon in the cross-coupling event.

Reaction of [(IPr)Ni(μ-Cl)]2 (1-Cl; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with ClMg{CH(SiMe3)2}·Et2O affords (IPr)Ni{CH(SiMe3)2} (2), a two-coordinate Ni(I) alkyl complex. An analogous two-coordinate aryl derivative, (IPr)Ni(dmp) (dmp = 2,6-dimesitylphenyl), can be similarly prepared from Li(dmp) and 1-Cl. Reaction of 2 with alkyl bromides gives the three-coordinate Ni(II) alkyl halide complex (IPr)Ni{CH(SiMe3)2}Br. Evidence for a radical mechanism is presented to explain the reaction of 2 with alkyl halides.

Synthesis and reactivity of two-coordinate Ni(I) alkyl and aryl complexes.

A nickel-catalyzed alkylation of succinic and glutaric anhydrides with alkyl- and arylzinc reagents has been developed. A dramatic olefin effect has been investigated resulting in the identification of several styrene-based promoters which show pronounced enhancements in reaction rate. The substrate scope with respect to electrophilic and nucleophilic coupling partners has been examined and found to be remarkably broad, allowing for rapid introduction of molecular complexity through the use of functionalized coupling partners. Regioselective alkylation of an unsymmetrical succinic anhydride and a profound effect of pendent coordinating olefins on reaction rate suggest a mechanism involving discrete oxidative addition of the nickel complex into the cyclic anhydride followed by a transmetalation event.

Bernd Nestler

Papers

A nickelacycle as propionic acid equivalent for carbon-carbon coupling reactions; application to the synthesis of C25 steroid carboxylic acids