57Fe NMR spectroscopy of ferrocenes derived from aminoferrocene and 1,1′-diaminoferrocene

Abstract

Three series of ferrocenes, derived from aminoferrocene Fc-NH2 and 1,1'-diaminoferrocene fc(NH2)2, were studied by 57Fe NMR spectroscopy. A marked decrease in 57Fe magnetic nuclear shielding with respect to ferrocene is observed if the nitrogen atom becomes part of a pi-acceptor linked to one or both cyclopentadienyl rings. In contrast, pi-donor properties of the amino group(s) affect delta57Fe to a much smaller extent. In the case of the fairly rigid structures of 1,3-diaza-2-element-[3]ferrocenophanes, a significant increase of 57Fe nuclear magnetic shielding is observed, in contrast to the corresponding [n]ferrocenophanes with n > 3. Structures of numerous of the ferrocene derivatives have been optimized for the gas phase by calculations (B3LYP/6-311 + G(d,p) level of theory), and 57Fe nuclear magnetic shieldings were calculated using these geometries. There is reasonable agreement in the trends for experimental and calculated data.

Synthesis, Characterization and Reactivity of Dinuclear and Trinuclear Aluminum‐Bridged Ferrocenophanes

“…The reported NMR spectroscopic data set [6] is incomplete and inconclusive in this respect. The 13 C NMR spectra of 4a,b (see Figure 3 for 4b) show all expected 13 C NMR signals in agreement with the proposed structure.…”

“…their peculiar somewhat broad features were striking. An example is shown for the 13 C NMR spectra in Figure 5, which also shows the inverse 1 H- 13 C heteronuclear shift correlation for the CH(fc) region. There are four different CH(fc) units clearly evident from the 1 H NMR spectra, of which two corresponding signals overlap in the 13 C NMR spectra.…”

“…Broad 13 C NMR signals are expected for 13 C nuclei linked to aluminum owing to partially relaxed scalar 27 Al-13 C spin-spin coupling as a result of efficient scalar nuclear relaxation [short values T 2 SC ( 13 C)] of the second kind. However, there is only one broad 13 C(fc)-Al NMR signal.…”

“…Then, the required four CH(fc) units with slightly exchange-broadened signals fit to the dynamic structure of 5. Moreover, the dynamic structure requires on average two broad 13 [10] ] of a mixture 4a/5a (in CD 2 Cl 2 at 23°C).…”

1,3,2-Diazaphospha-[3]ferrocenophanes. Molecular Structures and Multinuclear Magnetic Resonance Studies

“…(twist) (τ) a The definition of the angles α, β , γ and τ is given in refs. [25,28]; b ref. [13]; c one of two crystallographically independent molecules selected.…”