New Pd–NHC-complexes for the Mizoroki–Heck reaction

The synthesis and structural characterization of novel chelating N-aryl substituted palladium(II)–biscarbene-complexes is reported: 1,1′-bis(4-bromophenyl)-3,3′-methylene-diimidazoline-2,2′-diylidene-palladium(II)-dibromide, 1,1′-bis(4-methoxyphenyl)-3,3′-methylene-diimidazoline-2,2′-diylidene-palladium(II)-dibromide and 1,1′-bis(4-n-butoxyphenyl)-3,3′-methylenediimidazoline-2,2′-diylidene-palladium(II)-dibromide have been synthesized in good yields. The catalytic activity of these 1,1′-aryl-3,3′-methylenediimidazoline-2,2′-diylidene-palladium(II)-dihalogenide complexes was tested for the Mizoroki–Heck reaction in comparison to 1,1′-(bis)methyl-3,3′-methylenediimidazoline-2,2′-diylidene-palladium(II)-dihalogenide complexes and to 1,1′-bis(phenyl)-3,3′-methylene-diimidazoline-2,2′-diylidene-palladium(II)-dibromide. The activity of the aryl substituted catalysts is significantly higher compared to the methyl substituted NHC complexes. They also allow the coupling of arylchlorides with olefins.

Graphical abstractThe synthesis, structural characterization and catalytic application of novel bridged N-aryl substituted palladium(II)–biscarbenecomplexes in the Mizoroki–Heck reaction are reported. The activity of the investigated aryl substituted catalysts is significantly higher compared to the corresponding methyl substituted NHC complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide