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).