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]­(BF4) 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 D5h and D5d. 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)]­(BF4) (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.