Heterobimetallic Cu-dppf (dppf = 1,1′-Bis(diphenylphosphino) ferrocene) complexes with "click" derived Ligands: A combined structural, electrochemical, spectroelectrochemical, and theoretical study

Heterodinuclear complexes of the form [(dppf)Cu(L)](BF₄) (dppf = 1,1′-bis(diphenylphosphino)ferrocene), where L are the chelating, substituted 4,4′-bis(1,2,3-triazole) or 4-pyridyl(1,2,3-triazole) ligands, were synthesized by reacting [Cu(dppf)(CH₃CN)₂](BF ₄) with the corresponding "click" derived ligands. Structural characterization of representative complexes revealed a distorted-tetrahedral coordination geometry around the Cu(I) centers, with the donor atoms being the P donors of dppf and the N donors of the substituted triazole ligands. The "local-pseudo" symmetry around the iron center in all the investigated complexes of dppf is between that of the idealized D_5h and D_5d. Furthermore, for the complex with the mixed pyridine and triazole donors, the Cu-N bond distances were found to be shorter for the triazole N donors in comparison to those for the pyridine N donors. Electrochemical studies on the complexes revealed the presence of one oxidation and one reduction step for each. These studies were combined with UV-vis-near-IR and EPR spectroelectrochemical studies to deduce the locus of the oxidation process (Cu vs Fe) and to see the influence of changing the chelating "click" derived ligand on both the oxidation and reduction processes and their spectroscopic signatures. Structure-based DFT studies were performed to get insights into the experimental spectroscopic results. The results obtained here are compared with those of the complex [(dppf)Cu(bpy)](BF ₄) (bpy = 2,2′-bipyridine). A comparison is made among bpy, pyridyl-triazole, and bis-triazole ligands, and the effect of systematically replacing these ligands on the electrochemical and spectroscopic properties of the corresponding heterodinuclear complexes is investigated.