Co(II), Ni(II) and Cu(II) complexes of sterically encumbered N-arylimidoylamidine based [N,N′] chelating ligands

The reaction of mesitylamine (2,4,6-Me3C6H2NH2) with two equivalents of imidoylchloride, ArNC(Cl)Me (Ar = 2,4,6-Me3C6H2 or 2,6-iPr2C6H3) in the presence of Et3N yields neutral [N,N′] chelating ligands, [2,4,6-Me3C6H2N{C(Me)N(2,4,6-Me3C6H2)}2] (L1) and a pair of ligand isomers; symmetrical [2,4,6-Me3C6H2N{C(Me)N(2,6-iPr2C6H3)}2] (L2a) & unsymmetrical [2,6-iPr2C6H3NC(Me)N(2,6-iPr2C6H3)C(Me)N(2,4,6-Me3C6H2)] (L2b). An exclusive synthesis of the unsymmetrical isomer L2b has also been optimized by the reaction of a preformed amidine (2,6-iPr2C6H3)NH{C(Me)N(2,6-iPr2C6H3)} with the mesityl imidoylchloride. The three ligands have been thoroughly characterized by spectroscopic and X-ray diffraction methods (for L2a and L2b). The reaction of equimolar quantities of L1 with CoCl2·6H2O, NiBr2·xH2O, Cu(NO3)2·3H2O yields the corresponding mononuclear complexes, L1·CoCl2 (1), L1·NiBr2 (2) and L1·Cu(NO3)2 (3). Similarly, reaction of unsymmetrical ligand isomer L2b with CoCl2·6H2O, NiBr2·xH2O, or CuCl2 affords the complexes L2b·CoCl2 (4), L2b·NiBr2 (5) and L2b·CuCl2 (6), respectively. The solid state structures of complexes 1–6 have been investigated by single crystal X-ray structural analysis.

Graphical abstractSterically encumbered neutral [N,N′] chelating ligands based on N-arylimidoylamidine functionality have been prepared. The ligand [2,4,6-Me3C6H2N{C(Me)N(2,4,6-Me3C6H2)}2] (L1) and its complexes L1·CoCl2 (1), L1·NiBr2 (2), and L1·Cu(NO3)2 (3) have been prepared. Ligands [2,4,6-Me3C6H2N{C(Me)N(2,6-iPr2C6H3)}2] (L2a) and [2,6-iPr2C6H3NC(Me)N(2,6-iPr2C6H3)C(Me)N-2,4,6-Me3C6H2] (L2b) have also been synthesized. The ligands L2a and L2b are isomeric, the former is termed as symmetrical isomer and the latter is unsymmetrical, with respect to the substituents on N atoms of the ligand backbone. A synthetic route for exclusive synthesis of the unsymmetrical isomer L2b has been optimized and its mononuclear complexes as L2b·CoCl2 (4), L2b·NiBr2 (5) and L2b·CuCl2 (6) have also been reported. All compounds reported in this work have been characterized by spectroscopic and single crystal X-ray methods.Figure optionsDownload full-size imageDownload as PowerPoint slide