The Kinetics and Mechanisms of the Racemization of Tris(N,N′-dimethylethanediimine)iron(II)

Abstract

Abstract Tris(N,N′-dimethylethanediimine)iron(II) (trivial name: tris(glyoxal-bis-N-methylimine)iron(II)1)), [Fe(gmi)3]2+, has been resolved for the first time, and its racemization mechanism has been investigated in acid solutions. A mechanism similar to that for tris(2,2′-bipyridine)iron(II) was verified from the acid dependence of the racemization rate. At 69.4 °C, 30% of the racemization proceeded by means of an intramolecular bondrupture mechanism and the remainder by means of an intramolecular twist mechanism. The activation enthalpy and the activation entropy for the twist path were 148(ΔH\eweq⁄kJ mol−1) and 110(ΔS\eweq⁄J K−1 mol−1) respectively. These values were compared with 127 and 114 for [Fe(bpy)3]2+ (bpy=2,2′-bipyridine) and with 119 and 91 for [Fe(phen)3]2+ (phen=1,10-phenanthroline). The racemization rate was larger in organic solvents, increasing in the order water<nitromethane<formamide<dimethyl sulfoxide, which is the same as the order for the bpy and phen complexes. The rate was less dependent on the solvent in the order [Fe(phen)3]2+>[Fe(bpy)3]2+>[Fe(gmi)3]2+. A salt effect on the racemization rates was also observed.