ELECTROCHEMICAL REDUCTION OF SOME A(5)-CYCLOPENTADIENYL)(ETA(6)-ARENE)IRON(II)][PF6] COMPLEXES BEARING AN IMINE OR A NITRONE FUNCTION IN BENZYLIC POSITION OF THE ARENE LIGAND

The electrochemical reduction in basic hydro-organic media of mixtures of [(eta(5)-Cp) (eta(6)-benzophenone-N-(aryl)nitrone) Fe](+) 1a-d and [(eta(5)-Cp) (eta(6)-benzophenone anil) Fe](+) complexes 1'a-d led to the corresponding [(eta(5)-Cp) (eta(6)-alpha-(arylamino)diphenylmetha ne) Fe](+) cations 2a-d with good yields (85-90%). In a similar manner , various [(eta(5)-Cp) (eta(6)-9-(arylamino)fluorene) Fe](+) cations 4 a-i were synthesized (70-88% yield) in acidic hydro-organic media from the corresponding [(eta(5)-Cp) (eta(6)-fluorenone anil) Fe](+) 3a-i o r the [(eta(5)-Cp) (eta(6)-fluorenone-N-(2'-methoxycarbonyl phenyl)nit rone) Fe](+) derivative 3'i. According to H-1 NMR chemical shifts, the exo isomer is formed in the majority (exo:endo ca. 75:25) during elec trosynthesis of compounds 4a-i. We could explain these unexpected resu lts by an epimerization in the electrolysis media. The amines 4a,b wer e re-oxidized by oxygen into the starting imine 3a,b under very mild A l2O3-catalysis conditions (77-80% yield). (C) 1998 Elsevier Science S. A.