Facile oxidative addition of organic halides to heteroleptic and homoleptic Pd0-N-heterocyclic carbene complexes

摘要

Novel heteroleptic Pd~0 complexes with an N-heterocyclic carbene (NHC) ligand [(Me_3P)Pd(NHC)] (NHC = IPr, 1; SIPr, 2) were obtained from [Pd(CH_2=CHPh)(PMe_3)_2] and an equivalent of NHC [NHC = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) or 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr)]. Further treatments of complexes 1 and 2 with an additional equimolar NHCafforded the corresponding bis(NHC)-Pd~0 complexes [Pd(NHC)_2] (NHC = IPr, 3; SIPr, 4). Complexes 1-4 readily reacted with dichloromethane or chloroform to give C-Cl oxidative addition products. In addition, the reactivity of complex 2 toward other organic halides such as bromobenzene, trans-1,2-dichloroethylene, and 5,5′-dibromo-2,2′-bithiophene to produce the corresponding oxidative addition products was investigated. Finally, the ligand replacement of complex 1 with a chelating phosphane was examined.