2D HETCOR NMR spectra and unequivocal assignments of (E)- and (Z)-1-ferrocenyl-2-phenylethene, and (1E,3E)- and (1Z,3E)-1-ferrocenyl-4-phenyl-1,3-butadiene, (E)-1,2-diferreocenylethene, and (1E,3E)-1,4-diferrocenyl-1,3-butadiene in 13C NMR spectra

Abstract

Reaction of ferrocenecarbaldehyde with benzyltriphenylphosphorane and (E)-Cinnamyltriphenylphosphorane, respectively, afforded (E)- and (Z)-1-ferrocenyl-2-phenylethene ([(E)-5] and ([(Z)-5]), and (1E,3E)- and (1Z,3E)-1-ferrocenyl-4-phenyl-1,3-butadiene ([(1E,3E)-6] and [(1Z,3E)-6]), respectively, via the conventional Wittig reaction. An analogous reaction between (ferrocenylmethyl)triphenylphospphorane and (E)-1-ferrocenyl-2-formylethene 9 gave (1E,3E)-1,4-diferrocenyl-1,3-butadiene 8.From the 2D HETCOR, we observed that the C(3,4) of Cp ring (or C(para) of phenyl ring) resonates at a lower field than the C(2,5) of Cp ring (or C(ortho) of phenyl ring) in E isomers, whereas the C(2,5) (or C(ortho)) resonates at a lower field than the C(3,4) (or C(para)) in Z isomers. In the 1H NMR spectra, the H(2,5) (or H(ortho)) and the vinyl protons in E isomers resonate at a lower field than those of corresponding protons in Z isomers. The hypotheses to elucidate these data assignments are proposed.