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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-1-carboxylate (4). These organometallics are recognized as precursors for optically pure (1-ferrocenylethyl)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 83% of (E)-2 and 17% of (Z)-2, as well as into 76% of (E)-4 and 24% of (Z)-4. Crystal structures of the dominant isomers of 2 (two molecules within asymmetric unit) and 4 reveal that both compounds exist as (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.

[(methoxyimino)ethyl]ferrocene derivatives; E/Z isomerism; synthesis; crystal structure.

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