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

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.

57Fe NMR spectroscopy of ferrocenes bearing pi-acceptor substituents.

Ferrocene derivatives bearing pi-acceptor substituents in 1- or 1,1'-positions such as carbonyl group(s) (1, 2), a sulfinyl group (4) or boryl group(s) (5, 6, 9) and related [3]ferrocenophanes (3, 7, 10, 12, 13) and a [4]ferrocenophane (8) were studied by 57Fe NMR spectroscopy. The deshielding effect of the respective pi-acceptor substituent can be partially or fully compensated by distortion of the ferrocene geometry. Both aspects become apparent by comparing delta57Fe data of the [n]ferrocenophanes with those of related non-cyclic derivatives.