Synthesis and Structure of Geometric Isomers of 1-[(methoxyimino)ethyl]- ferrocene and Methyl 1'-[(methoxyimino)ethyl]ferrocene-1-carboxylate

Here we report synthesis, spectral data and single-crystal X-ray molecular and crystal structures of (E)-1-[(methoxyimino)ethyl] ferrocene (2) and (E)-methyl 1'-[(methoxyimino)ethyl]ferrocene-1carboxylate (4). These organometallics are recognized as precursors for optically pure (1ferrocenylethyl)amine (Fea) and 1'-(1-aminoethyl)ferrocene-1-carboxylic acid (Fcca) derivatives. The (E/Z)mixtures of the title compounds 2 and 4 were obtained in ≈90 % yield by the action of methoxyamine hydrochloride on acetylferrocene (1) and 1'-acetylferrocene-1-carboxylic acid (3). By means of preparative thin layer chromatography the synthesized compounds were separated into 75 % of (E)-2 and 15 % of (Z)-2, as well as into 68 % of (E)-4 and 22 % of (Z)-4. Crystal structures of the dominant isomers of 2 (two molecules within asymmetric unit) and 4 confirm that both compounds exist in (E)-forms. The ferrocenyl moieties deviate slightly from eclipsed conformation in 2 and 4. The intramolecular C−H···O contact in the C(CH3)−N−OCH3 group (2.670(7) Å in the second molecule of 2 and 2.644(6) Å in 4) can be regarded as a weak intramolecular hydrogen bond. The crystal packings of 2 and 4 are characterized only by van der Waals forces.