Isomerism and redox properties of 1-ferrocenyl-1,3-butanedionate complexes

The ferrocenyl diketone [(C5H5)Fe(C5H4)COCH2COCH3] has been used to form neutral metal complexes of the 1-ferrocenyl-l,3-butanedionate ligand [(C5H5)Fe(C5H4)COCHCOH3]−: the aluminium complex of this ligand, [Al{(C5H5)Fe(C5H4)COCHCOCH3}3], has been characterised by 1H and 13C NMR as a 2:3 mixture of fac and mer isomers, having C3 and C1 molecular symmetry respectively. Electrochemical studies show that each peripheral 1-ferrocenyl-1,3-butanedionate ligand L of both MIIL2 (M = Co, Ni, Cu) and MIIIL3 (M = Al, Cr, Mn, Fe) complexes undergoes reversible one-electron oxidation at potential values essentially overlapping each other. This means that the central metal ions prevent any electronic communication between the two or three ferrocene fragments. In addition to these reversible ferrocene-centred oxidations, there are reversible one-electron reductions centred at M for MnL3 and FeL3 (but not for CrL3 or AIL3), but the metal-centre reductions of MIIL2 are irreversible owing to further reactions following reduction.