Fluorophosphoniums as Lewis acids in organometallic catalysis: application in cobalt-catalyzed carbonylation of β-lactones

Within the context of the development of phosphorus-based Lewis acids, we report herein the synthesis of four fluorophosphonium organic Lewis acids, with tetracarbonyl cobaltate as counter-anion: [R3PF]+[Co(CO)4]- (with R = o-Tol, Cy, iPr, and tBu). These novel ion pairs were fully characterized by NMR and IR spectroscopy, elemental analysis, and, for three of them, X-ray diffraction. The catalytic activities of these ion pairs were investigated for the carbonylation of β lactones to succinic anhydrides. [tBu3PFCo(CO)4] IV (3 mol%) afforded 91 % of succinic anhydride after 16 h at 80 °C, at a very mild pressure of 2 bar of carbon monoxide. To our knowledge, this work is the first report on using fluorophosphoniums as main-group Lewis acids in a transition metal-catalyzed reaction.