Synthesis of tungsten compounds with Schiff base ligands prepared from ferrocenecarboxaldehyde: Observation of the migration of an imine double bond

The one-pot reactions of ferrocenecarboxaldehyde, W(CO)4(pip)2 (pip = piperidine) and either 2-(aminomethyl)pyridine or 2-(2-aminoethyl)pyridine lead to clean formation of pyridine imine products W(CO)4(η2-NC5H4CHNCH2C5H4FeCp) (1) and W(CO)4(η2-NC5H4C2H4NCHC5H4FeCp) (2), respectively. Crystal structures of the two compounds show that in 1 the imine double bond has migrated so that it is conjugated with the pyridine ring while in 2 the imine double bond remains conjugated with the cyclopentadienyl ring. This finding is reinforced by a comparison of dihedral angles in each molecule. IR, NMR and electronic spectra each highlight the differences between the two compounds. Crystal data for C21H16FeN2O4W (1): monoclinic P2(1)/c, a = 12.768(2) Å, b = 13.593(2) Å, c = 12.981(2) Å, β = 119.46°, V = 1961.6(4) Å3, Z = 4; C22H18FeN2O4W (2): monoclinic P2(1)/c, a = 16.759(1) Å, b = 8.8612(7) Å, c = 13.802(1) Å, β = 95.998(1)°, V = 2038.4(3) Å3, Z = 4.

Graphical abstractThe reactions of ferrocenecarboxaldehyde, W(CO)4(pip)2 (pip = piperidine) and either 2-(aminomethyl)pyridine or 2-(2-aminoethyl)pyridine lead to formation of W(CO)4(η2-NC5H4CHNCH2C5H4FeCp) (1) and W(CO)4(η2-NC5H4C2H4NCHC5H4FeCp) (2), respectively. Crystal structures show that in 1 the imine double bond has migrated and is conjugated with the pyridine ring. Spectroscopic measurements highlight the differences between the compounds.Figure optionsDownload full-size imageDownload as PowerPoint slide