aIsolated yields shown are of a mixture of 2aq and 2ar. Standard C–P bond formation: 1as (1.0 equiv), Tf2O (1.0 equiv), PPh3 (1.1 equiv), DBU (1.0 equiv) CH2Cl2, −78 °C to rt. Switch C–P bond formation: 1as (1.0 equiv), Tf2O (2.0 equiv), PPh3 (2.0 equiv), NEt3 (2.0 equiv) CH2Cl2, −78 °C to rt. Co-catalysis: 10 mol % Co(acac)3, 10 mol % L3, N-Methylimidazole (1.5 equiv), THF, 50 °C.