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.