Issue 67, 2014

5-Ferrocenyl-2,2′-bipyridine ligands: synthesis, palladium(ii) and copper(i) complexes, optical and electrochemical properties

Abstract

Two ferrocene-appended 2,2′-bipyridine ligands, 5-ferrocenyl-2,2′-bipyridine (Fc-bipy) and 5-ferrocenyl-5′-methyl-2,2′-bipyridine (Fc-bipy-Me) metalloligands were synthesised using palladium(0) catalysed Suzuki–Miyaura cross-coupling reaction. Their coordination chemistry with palladium(II) and copper(I) ions was examined. The molecular structures of several complexes, including [Pd(Fc-bipy-Me)(Cl)2], [Pd(Fc-bipy)(py)2](SbF6)2, [Pd(Fc-bipy)(DMAP)2](SbF6)2, [Pd(Fc-bipy-Me)(DMAP)2](SbF6)2, and [Cu(Fc-bipy)(6,6′-dimesityl-2,2′-bipyridine)](PF6) and [Cu(Fc-bipy-Me)(6,6′-dimesityl-2,2′-bipyridine)](PF6) were determined using X-ray crystallography. 1H and 13C NMR spectra and high resolution electrospray mass spectrometry (HR-ES-MS) experiments confirmed that the majority of the complexes are stable in solution. The exceptions were [Pd(Fc-bipy)(DMAP)2](SbF6)2 and [Pd(Fc-bipy-Me)(DMAP)2](SbF6)2 which were found to disproportionate to give equilibrium mixtures containing [Pd(Fc-bipy)2](SbF6)2 and [Pd(DMAP)4](SbF6)2. The optical absorption and electrochemical properties of these complexes were compared to those of the parent ligands. The 5-ferrocenyl-2,2′-bipyridine ligands are yellow/orange in colour with the expected weak d–d transition found at ∼450 nm. The absorption bands of the palladium(II) and copper(I) complexes are red-shifted relative to the free ligands and show enhanced molar absorptivity. The complexes all display strong MLCT absorptions in the visible spectrum, the palladium(II) compounds are deep purple (λmax = ∼540–560 nm), while the copper(I) complexes are red-brown (λmax = ∼470 nm). Electrochemical investigations showed that all the compounds displayed the expected chemically reversible one-electron oxidation of the ferrocenyl group. The reduction potential of the redox-active ferrocene unit was anodically shifted, relative to the free ligand, upon complexation to the metal ions. The copper(I) complexes displayed an additional reversible oxidation wave that was assigned as a Cu(II)/Cu(I) redox process.

Graphical abstract: 5-Ferrocenyl-2,2′-bipyridine ligands: synthesis, palladium(ii) and copper(i) complexes, optical and electrochemical properties

Supplementary files

Article information

Article type
Paper
Submitted
05 Jun 2014
Accepted
06 Aug 2014
First published
06 Aug 2014

RSC Adv., 2014,4, 35726-35734

Author version available

5-Ferrocenyl-2,2′-bipyridine ligands: synthesis, palladium(II) and copper(I) complexes, optical and electrochemical properties

S. Ø. Scottwell, K. J. Shaffer, C. J. McAdam and J. D. Crowley, RSC Adv., 2014, 4, 35726 DOI: 10.1039/C4RA05333H

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