2,3-Diamino-4,5-diarylcyclopentadienone iron carbonyl complexes as catalysts for reductive amination reactions†

The reaction of dipiperidinoacetylene, (CH₂)₅NCCN(CH₂)₅, with a series of 2,3-diarylcyclopropenones (Ar)₂C₃O (Ar = phenyl, 4-tert-butylphenyl, 2,5-dimethylphenyl, 4-trifluoromethylphenyl) afforded 2,3-dipiperidino-4,5-diarylcyclopentadienones, which were used to prepare cyclopentadienone (CPD) iron tricarbonyl complexes [(CPD)Fe(CO)₃] by the reaction with Fe₂(CO)₉. Subsequent treatment with trimethylamine-N-oxide in the presence of acetonitrile afforded the corresponding acetonitrile complexes [(CPD)Fe(CO)₂(NCCH₃)], which were used as catalysts for the reductive amination of citronellal with various secondary amines under 5 bar of dihydrogen pressure. The first iron-catalysed reductive amination for the preparation of the pharmaceutically important antidepressant sertraline is also reported.