Fluorophosphoniums as Lewis acids in organometallic catalysis: application to the carbonylation of β-lactones.

We describe the synthesis and characterisation of four organic Lewis acids based on fluorophosphoniums, with tetracarbonyl cobaltate as the counter-anion: [R 3 PF] + [Co(CO) 4 ] - (with R = o -Tol, Cy, i Pr, and t Bu). Their catalytic activity was investigated for the carbonylation of β-lactones to succinic anhydrides. In the presence of [ t Bu 3 PF] + [Co(CO) 4 ] - IV (3 mol%), 90% of succinic anhydride was afforded from β-propiolactone after 16 h at 80 °C, at a very mild pressure of 2 bar of carbon monoxide. Our study sets the first example of the use of a main-group cation as a Lewis acidic partner in the cobalt-catalyzed carbonylation of β-lactones.