Electrochemical evidence for hemilabile coordination of 1,3-dimethyllumazine to [1,1′-Bis(diorganophosphino)ferrocene]copper(I)

Abstract

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-dimethyllu-mazine, 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. (Figure Presented) © 2014 American Chemical Society.