Influence of Ligand Backbone and Solvent on Product Distribution of Cu(II) Salts with Imine Based Ligands

The current investigation examines the reactivity of imine based ligands while bound to a copper(II) metal center. The ligands were synthesized by reacting two equivalents of a pyridine aldehyde (R = -H, -Me, -OMe) with ethylenediamine and characterized by 1H NMR and IR spectroscopies. Analogous reactions were carried out in a 1:1 mole ratio of Cu(NO3)2·2.5 H2O or Cu(ClO4)2·5 H2O with each ligand (-Me or -OMe) in methanol. Reactions with the -OMe ligand derivative, PyOMe2(en), and the nitrate salt, resulted in formation of three different products, while only one product is obtained with the perchlorate salt. Compound 1 is found to be a dimeric species with one PyOMe2(en) ligand bridging between two Cu(II) metal centers. The remainder of the coordination sphere around each Cu(II) is composed of the hydrolyzed ligand (PyOMe(enH2)). The Cu(II) center in 2 is found to have a ligand in which both imine groups have reacted with solvent, and the product in 3 has a copper ligated to the partially hydrolyzed ligand. Reaction with the nitrate salt and the -Me analogue (PyMe2(en)) resulted in the formation of complex 4, which contains a ligand frame in which half has hydrolyzed to give bound amine (PyMe(enH2). Reactions with the perchlorate salt and PyMe2(en) resulted in the formation of complex 5, which contains a version of the hydrolyzed ligand where oxygen has replaced the nitrogen of ethylenediamine and methanol has been added. When the perchlorate salt reacted with PyOMe2(en), product 1 was observed. Further investigation is underway to determine the origin of the reactivity within this set.