Wydział Chemii

D. Canseco-Gonzalez

Andrzej Gniewek

Michał S. Szulmanowicz

H. Müller-Bunz

Anna M. Trzeciak

M. Albrecht

2012

Chemistry-A European Journal

18

6055-6062

10.1002/chem.201103719

Naukowa

Angielski

Artykuł

A series of PEPPSI-type palladium(II) complexes was synthesized that contain 3-chloropyridine as an easily removable ligand and a triazolylidene as a strongly donating mesoionic spectator ligand. Catalytic tests in Suzuki-Miyaura cross-coupling reactions revealed the activity of these complexes towards aryl bromides and aryl chlorides at moderate temperatures (50 °C). However, the impact of steric shielding was the inverse of that observed with related normal Nheterocyclic carbenes (imidazol-2-ylidenes) and sterically congested mesityl substituents induced lower activity than small alkyl groups. Mechanistic investigations, including mercury poisoning experiments, TEM analyses, and ESI mass spectrometry, provide evidence for ligand dissociation and the formation of nanoparticles as a catalyst resting state. These heterogeneous particles provide a reservoir for soluble palladium atoms or clusters as operationally homogeneous catalysts for the arylation of aryl halides. Clearly, the substitution of a normal N-heterocyclic carbene for a more basic triazolylidene ligand in the precatalyst has a profound impact on the mode of action of the catalytic system.

cross-coupling, Heterogeneous catalysis, homogeneous catalysis, mesoionic carbene, palladium

http://dx.doi.org/10.1002/chem.201103719

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