Structure of heteroannularly disubstituted ferrocene derivatives containing acetamido group

Methyl 1′-(acetamido)ferrocene-1-carboxylate (2), 1′-acetamidoferrocene-1-carboxazide (4) and methyl 1′-(1-acetamidoethyl)ferrocene-1-carboxylate (6) have been prepared and fully characterized. X-ray single crystal analysis showed that acetamido group in 2 and 4, methoxycarbonyl group in 2 and 6 and azidocarbonyl group in 4 are coplanar with adjacent cyclopentadienyl rings. In compound 6, acetamido group is perpendicular with respect to the plane of the cyclopentadienyl ring. Ferrocene cyclopentadienyl rings in 2 and 6 adopt an eclipsed conformation, while in 4 they deviate only slightly from this conformation. The molecules of 2 and 6 are self-assembled by one NH⋯O intermolecular hydrogen bond into infinite chains, while NH⋯O hydrogen bond in derivative 4 forms centrosymmetric dimer. 1H NMR and IR spectra measured in diluted solutions (nonpolar solvents) showed that acetamido-ester 2 and acetamido-azide 4 existed in a free forms 2A/4A, while at higher concentration they have tendency to form intermolecular hydrogen bonds. Solutions of conjugate 6 contained a mixture of conformers stabilized by intramolecular-hydrogen-bond 6B and open form 6A.