Palladium(II) pyrazolin-4-ylidenes: Remote N-heterocyclic carbene complexes and their catalytic application in aqueous Suzuki-Miyaura coupling

Abstract

Two monocationic complexes of pyrazole-derived remote carbene ligands of the type trans-[PdI(rNHC)(PPh3)2]+OTf - {rNHC = 2-ethyl-3,5-dim -1-phenylpyrazolin-4-ylidene (6a), 1-ethyl-2,3,5-trimethylpyrazolin-4-ylidene (6b)} were prepared by oxidative addition of 4-iodo-1,2,3,5-tetrasubstituted pyrazolium triflate salts to [Pd2(dba)3]/PPh3 in good yields. Both compounds were fully characterized by multinuclei NMR spectroscopies, electrospray ionization mass spectrometry, and X-ray diffraction analysis. A comparative study on the aqueous Suzuki-Miyaura catalytic activities of these cationic complexes with their previously reported neutral counterparts reveals the superiority of the former. © 2007 American Chemical Society.