Novel η³-Allylpalladium−Pyridinylpyrazole Complex:  Synthesis, Reactivity, and Catalytic Activity for Cyclopropanation of Ketene Silyl Acetal with Allylic Acetates

Novel cationic η 3 -allylpalladium−pyridinylpyrazole complexes 1a and 1b were synthesized from 3-alkyl-5-(2-pyridinyl)pyrazole and η 3 -allylpalladium chloride dimer in the presence of AgBF 4 . Cationic complexes 1a and 1b were converted into neutral complexes 2a and 2b under basic conditions. These complexes were characterized by 1 H, 13 C, and 15 N NMR studies. Neutral complexes 2a and 2b have high catalytic activity for cyclopropanation of ketene silyl acetals with allylic acetates. Comparison of the cationic and neutral complexes and the reaction mechanism of cyclopropanation were discussed.