ELECTRON-TRANSFER-INDUCED HAPTOTROPIC ISOMERIZATION OF FLUORENYLMANGANESETRICARBONYL COMPLEXES - ELECTROCATALYTIC AND CHAIN MECHANISMS

The electrochemical reduction of (eta(6)-C13H9)Mn(CO)(3) (1, where C13 H9 - fluorenyl) has been studied in THF by cyclic voltammetry and prep arative controlled potential electrolysis. One-electron reduction of 1 to the corresponding 19-electron radical anion 1(.-) is accompanied b y the haptotropic isomerization of the latter to the radical anion (et a(5)-C13H9)Mn(CO)(3)(.-) (2(.-)), which is oxidized at the electrode t o neutral complex 2. Electron-transfer induced isomerization 1 --> 2 i s an electrocatalytic process with current efficiency of 600 %, which can be also promoted by catalytic amounts (less than or equal to 20 %) of the chemical reducing agents (benzophenone radical anion or sodium amalgam). If the reaction is chemically induced, the radical anion 2( .-) is oxidized by initial complex 1; as a result the electron-transfe r induced isomerization 1 --> 2 proceeds by a chain mechanism. The inf luence of the electronic state (18e(-)/19e(-)) of eta(6)- and eta(5)-f luorenyl complexes on the position of the equilibrium of the intra-rin g haptotropic isomerization reaction is discussed.