Electrochemical Evidence for Hemilabile Coordination of 1,3-Dimethyllumazine to [1,1′-Bis(diorganophosphino)ferrocene]copper(I) JanaRajkumar SarkarBiprajit StrobelSabine MobinShaikh M. KaimWolfgang FiedlerJan 2014 The complex cations [Cu­(dippf)­(DML)]<sup>+</sup> ([<b>1</b>]<sup>+</sup>) and [Cu­(dppf)­(DML)]<sup>+</sup> ([<b>2</b>]<sup>+</sup>), where dippf = 1,1′-bis­(diisopropylphosphino)­ferrocene, dppf = 1,1′-bis­(diphenylphosphino)­ferrocene, and DML = 1,3-dimethyllumazine, were prepared and crystallized as BF<sub>4</sub><sup>–</sup> or PF<sub>6</sub><sup>–</sup> salts. Structure determinations of the tetrafluoroborates revealed asymmetric O<sup>4</sup>,N<sup>5</sup> chelation of DML to copper­(I) with longer Cu–O bonds of about 2.25 Å. Reversible oxidation to [<b>1</b>]<sup>2+</sup> and [<b>2</b>]<sup>2+</sup> proceeds at the ferrocene units, while reduction leads to the neutral radical complexes [<b>1</b>] and [<b>2</b>] 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.