Synthesis of Bis(phosphinoferrocenyl) Copper Complexes from Zwitterionic Quinonoid Ligands and Their Structural and Redox Properties

Reactions of N,N′-di-n-butyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium L¹, or N,N′-diisopropyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium L² with [{(dppf)Cu}₂(μ−Cl)₂] (dppf = 1,1′-bis(diphenylphosphino)ferrocene) or [{(dispf)Cu}₂(μ−Cl)₂] (dispf = 1,1′-bis(diisopropylphosphino)ferrocene) led to the formation of the heterodinuclear complexes [(dppf)(CuL¹_−H)] (2), [(dppf)(CuL²_−H)] (3), [(dispf)(CuL¹_−H)] (4), and [(dispf)(CuL²_−H)] (5). The crystal structure of L² was determined by X-ray diffraction and shows that the molecule exists in a 6π + 6π zwitterionic form, with two chemically connected but electronically nonconjugated π-subunits. The crystal structures of complexes 2−4 show a distorted tetrahedral coordination environment for the Cu(I) center and a more localized π-system for the ligands. Cyclic voltammetry on the ligands and complexes indicates various redox processes. The first oxidation of the complexes leads to an electron paramagnetic resonance supported formulation where the ligand radical is bound to Cu(I). UV−visible spectroscopy of the ligands and the complexes is also reported and discussed.