Phospha-palladacycles and N-heterocyclic carbene palladium complexes: efficient catalysts for CC-coupling reactions

Due to the great importance of palladium-catalyzed Heck-type reactions in scientific and industrial chemistry, a lot of publications and reviews have been published during the last years describing this matter under different aspects. This article presents a summary of catalytic applications of palladium complexes with phosphorus ligands containing a metallated sp³-carbon centre (“palladacycles”) or with N-heterocyclic carbene ligands in C-C and C-N coupling reactions of aryl halides including recent results of mechanistic discussions about their role in the catalytic cycle.     

Catalysis of CC-coupling reactions by cyclopropenylidene palladium complexes

Several mixed palladium(II) complexes bearing 2,3-diarylcyclopropenylidene ligands (aryl = phenyl, mesityl, naphthyl) and triaryl- and trialkylphosphines have been prepared. Single crystal structure details of one of the dimeric chloro-bridged complexes as well as of two monomeric phosphine substituted complexes are presented and compared with appropriate structural features of similar 2,3-diaminocyclopropenylidene- and cycloheptatrienylidene complexes. The new complexes were tested as catalysts in Suzuki-Mijaura coupling reactions with bromo- and chloroarenes and their catalytic activity compared with that of analogous NHC- and cycloheptatrienylidene complexes.     

Synthesis and characterization of phospha-palladacycles and their catalytic properties in the olefination of chloro- and bromoarenes

Acetylacetonates of phospha-palladacycles are new catalysts in the Heck coupling of aryl chlorides and bromides with styrene. Turnover numbers (TON) of much higher than 300,000 and product yields up to 99% are obtained.