Electrochemical Evidence for Hemilabile Coordination of 1,3-Dimethyllumazine to [1,1′-Bis(diorganophosphino)ferrocene]copper(I)

The complex cations [Cu­(dippf)­(DML)]+ ([1]+) and [Cu­(dppf)­(DML)]+ ([2]+), where dippf = 1,1′-bis­(diisopropylphosphino)­ferrocene,
dppf = 1,1′-bis­(diphenylphosphino)­ferrocene, and DML = 1,3-dimethyllumazine,
were prepared and crystallized as BF4– or PF6– salts. Structure determinations
of the tetrafluoroborates revealed asymmetric O4,N5 chelation of DML to copper­(I) with longer Cu–O bonds
of about 2.25 Å. Reversible oxidation to [1]2+ and [2]2+ proceeds at the ferrocene
units, while reduction leads to the neutral radical complexes [1] and [2] with the unpaired electron localized
on the DML ligand. The occurrence of two voltammetric steps for the
one-electron-reduction process is attributed to a two-species equilibrium
caused by the hemilabile coordination of DML. Electrochemical and
spectroelectrochemical measurements (UV–vis, IR) reveal increased
coordination lability of the reduced complexes and their slow fragmentation.