Mono-, bi-, and trinuclear Cu^II-Cl containing products based on the tris(2-pyridylmethyl)amine chelate derived from copper(I) complex dechlorination reactions of chloroform

The ligand TMPA (tris(2-pyridylmethyl)amine) and its copper complexes have played a prominent role in recent (bio)inorganic chemistry studies; the copper(I) complex [Cu^I(TMPA)(CH₃CN)]⁺ possesses an extensive dioxygen reactivity, and it is also known to effect the reductive dechlorination of substrates such as dichloromethane and benzyl and allyl chlorides. In this report, we describe a set of new analogues of TMPA, ligand 6TMPAOH, binucleating Iso-DO, and trinucleating SYMM. Copper(I) complexes with these ligands and a previously described binucleating ligand DO react with chloroform, resulting in reductive dechlorination and production of [Cu ^II_x(L)Cl_x]^x+ (x = 1, 2, or 3). X-ray crystal structures of [Cu^II(6TMPAOH)Cl]PF₆, [Cu ^II₂(Iso-DO)Cl₂](PF₆)₂, [Cu^II₂(DO)Cl₂](PF₆)₂, and [Cu₃(SYMM)-Cl₃](PF₆)₃ are presented, and the compounds are also characterized by UV-vis and EPR spectroscopies as well as cyclic voltammetry. The steric influence of a pyridyl 6-substituent (in the complexes with 6TMPAOH, Iso-DO, and SYMM) on the solid state and solution structures and redox potentials are compared and contrasted to those chlorocopper(II) complexes with a pyridyl 5′-substituent (in [Cu^II₂(DO)Cl₂](PF₆)₂ and in [Cu^II(TMPA)Cl]⁺). Some insights into the reductive dechlorination process have been obtained by using ²H NMR spectroscopy in following the reaction of [Cu₂(Iso-DO)(CH ₃CN)₂](PF₆]₂ with CDCl₃, in the presence or absence of a radical trap, 2,4-di-tertbutylphenol.