Mechanochemical synthesis and spectroscopic properties of 1,1′-ferrocenyldiacrylonitriles: the effect of para-substituents

Abstract

An efficient and simple solvent-free mechanochemical approach for the synthesis of 1,1′-ferrocenyldiacrylonitriles was achieved by grinding together 1,1′-ferrocenedicarboxaldehyde (1) and phenylacetonitriles. A range of 1,1′-ferrocenyldiacrylonitriles and ferrocenylacrylonitriles (2–7) were synthesized within short reaction times, with water as the only by-product. In a similar manner, grinding together ferrocenemonocarboxaldehyde (8) and phenylenediacetonitrile yielded phenylene-3,3′-bis-(ferrocenyl)diacrylonitrile (9) and 3-ferrocenyl-2-(acetonitrophenyl)acrylonitrile (10). The yield and selectivity towards formation of ferrocenyldiacrylonitriles was strongly influenced by the electronegativity of the para-substituent on the phenyl ring of phenylacetonitriles. The compounds were characterized using NMR, IR, and UV–visible spectroscopy and HR-MS. Cyclic voltammetry measurements of selected compounds highlighted the role of ligands in tuning the electrochemical properties of 1,1′-ferrocenyldiacrylonitriles. X-ray crystallographic analysis highlighted the effect of the electronegativity of the para-substituent on the conformation of cyclopentadienyl rings attached to a ferrocenyl moiety.

Graphical Abstract

Mechanochemical synthesis of ferrocenylacrylonitriles.

Keywords:

• 1,1′-Ferrocenyldiacrylonitriles
• 1,1′-Ferrocenedicarboxaldehyde
• Solvent-free
• Green chemistry
• Mechanochemical

Acknowledgements

This research was financed by the National Research Foundation (NRF) and the University of KwaZulu-Natal (UKZN). Lucy M. Ombaka thanks the UKZN College of Agriculture, Engineering and Science for the award of a postgraduate bursary. We are also grateful to Prof. B.S. Martincigh, Dr R.S. Mwakubambanya, Godfrey Keru, and Mombeshora Tonde for their critical comments on the manuscript.