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 Pd^II(Ph)(CF₃) complexes. This study reveals that increasing the size of the phosphine substituents results in an enhanced rate of Ph–CF₃ coupling, with (D^tBPF)Pd(Ph)(CF₃) (D^tBPF = 1,1′-bis(di-tert-butylphosphino)ferrocene) being the most reactive complex. The mechanism of Ph–CF₃ bond formation from both (D^tBPF)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 Pd^II centers. An alternative pathway involving α-fluoride elimination and subsequent PhF₂C–F coupling from Pd^II(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).