Facile Oxidative Addition of Organic Halides to Heteroleptic and Homoleptic Pd0-N-Heterocyclic Carbene Complexes

Novel heteroleptic Pd-0 complexes with an N-heterocyclic carbene (NHC) ligand [(Me3P)Pd(NHC)] (NHC = IPr, 1; SIPr, 2) were obtained from [Pd(CH2=CHPh)(PMe3)(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 NHC afforded 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.