Synthesis of Stable Diarylpalladium(II) Complexes: Detailed Study of the Aryl-Aryl Bond-Forming Reductive Elimination.
The synthesis of diarylpalladium(II) complexes by twofold aryl C-H bond activation was developed. These intermediates of oxidative cyclization reactions are stabilized by chelation with acetyl groups while still maintaining sufficient reactivity to study their reductive elimination. Four distinct triggers were found for the reductive elimination of these complexes to dibenzofurans and carbazoles. Thermal elimination occurs at very high temperatures, whereas ligand-promoted and oxidatively induced reductive eliminations proceed readily at room temperature. Under these conditions, no isomerization occurs. In contrast, weak Brønsted acids, such as acetic acid, lead to a sequence of proto-demetalation, isomerization to a κ(3) -diarylpalladium(II) complex, and reductive elimination to non-symmetrical cyclization products.
Department of Chemistry, Technische Universität Dresden, Bergstrasse 66, 01069, Dresden, Germany.
Tobias
T
Gensch
Department of Chemistry, Technische Universität Dresden, Bergstrasse 66, 01069, Dresden, Germany.
Nils
N
Richter
Department of Chemistry, Technische Universität Dresden, Bergstrasse 66, 01069, Dresden, Germany.
Gabriele
G
Theumer
Department of Chemistry, Technische Universität Dresden, Bergstrasse 66, 01069, Dresden, Germany.|A. E. Arbuzov Institute of Organic and Physical Chemistry, Russian Academy of Sciences, Arbuzov Str. 8, Kazan, 420088, Russia.
Olga
O
Kataeva
Department of Chemistry, Technische Universität Dresden, Bergstrasse 66, 01069, Dresden, Germany. hans-joachim.knoelker@tu-dresden.de.
Hans-Joachim
HJ
Knölker
C−H bond activation; metallacycles; palladium; reaction mechanisms; reductive elimination