Copper complexes of tripodal κ6N-donor ligands: A structural, EPR spectroscopic and electrochemical study

Abstract

A new tris(pyridylhydrazonyl)methane ligand, HC[N(Me)NC(H)Py]3 (L2) (Py=pyridyl), has been synthesized. The latter is accessible from triethyl orthoformate and 2-(2-methylhydrazono)methylpyridine in 63% isolated yield. We have investigated its coordination chemistry towards copper ions and compared the results with those obtained for the recently developed multifunctional ligand, (S)P[N(Me)NC(H)Py]3 (L1). The copper(II) complexes [Cu(L1)](OTf)2 (3) and [Cu(L2)](OTf)2 (4) (OTf=triflate, (O3SCF3)−) are mononuclear with the cations coordinated by three imino and three pyridine nitrogen atoms. Almost axial symmetric EPR spectra have been obtained in frozen solutions at X-band. The spectra show resolved hyperfine couplings to the copper nuclei on one of the three g values. X-ray structural analyses revealed in each case a cis bond distortion and a trigonal twist due to Jahn–Teller effects. The CuII/CuI reduction potentials of 3 and 4 were shown to be remarkably low (E1/20=−0.11V for 3; E1/20=−0.34V for 4), especially for 3 consisting of the phosphorus supported ligand L1. The corresponding copper(I) complexes [Cu(L1)](OTf) (5) and [Cu(L2)](OTf) (6) are accessible by reduction using decamethyl ferrocene. Both copper(I) complexes have been characterized in detail including X-ray structure analyses.