An electron-transfer induced migratory insertion reaction originating froma 19-electron cobaltacyclic anion

The cyclopentadienyl cobaltafluorenyl carbonyl complex Cp(CO)CoC12H8 (3) is reduced in THF in a one-electron irreversible process. The reduction produ cts include the fluorenone radical anion, Fl(-), which is proposed to arise through migratory insertion of the CO ligand into the metallacyclic Co-C b ond of the 19-electron complex 3(-). Electrochemical and IR analyses show t hat bulk electrolysis under N-2 gives 1/3 equiv. each of Fl(-) and CpCo(CO) (2) and 2/3 equiv. of a 17-electron anion [CpCoC12H8](-) (2(-)) Under CO th e yield of Fl(-) is quantitative. The insertion product is also formed when the reduction of the analogous phosphine complex Cp(PPh3)CoC12H8 is perfor med under CO. An equilibrium between 17- and 19-electron compounds is postu lated to account for the synthetic and voltammetric observations. When the cobaltacycle Cp(PPh3)CoC4Ph4 (5) is reduced under carbon monoxide, the GO-i nsertion product is the pi-cyclopentadienone complex CpCo(eta(4)-C4P4O) (8) . (C) 2000 Elsevier Science S.A. All rights reserved.