Aryl–CF3 Coupling from Phosphinoferrocene-Ligated Palladium(II) Complexes

This article describes a detailed investigation of ligand effects on Ph–CF3 coupling from phosphinoferrocene-ligated PdII(Ph)(CF3) complexes. This study reveals that increasing the size of the phosphine substituents results in an enhanced rate of Ph–CF3 coupling, with (DtBPF)Pd(Ph)(CF3) (DtBPF = 1,1′-bis(di-tert-butylphosphino)ferrocene) being the most reactive complex. The mechanism of Ph–CF3 bond formation from both (DtBPF)Pd(Ph)(CF3) and (DiPrPF)Pd(Ph)(CF3) (DiPrPF = 1,1′-bis(diisopropylphosphino)ferrocene) was interrogated experimentally and computationally. These studies implicate a pathway involving concerted Ph–CF3 bond-forming reductive elimination from the four-coordinate PdII centers. An alternative pathway involving α-fluoride elimination and subsequent PhF2C–F coupling from PdII(CF2Ph)(F) intermediates was also evaluated but was ruled out based on DFT as well as the independent synthesis and reactivity studies of (DiPrPF)Pd(CF2Ph)(F).