Dinuclear manganese complexes containing 1,4-dimethyl-1,4,7-triazacyclononane ligands as well as carboxylato and oxo bridges

Abstract

The reaction of 1,4-dimethyl-1,4,7-triazacyclononane (L-Me 2) with MnCl 2 · 4H 2O in acetonitrile gives, in the presence of sodium formate, hydrogen peroxide, triethylamine and KPF 6, the dinuclear Mn(III)–Mn(IV) complex cation [(L-Me 2) 2Mn 2(O) 2(OOCH)] 2+ ( 1) which crystallises as the hexafluorophosphate salt.The analogous reaction with sodium benzoate, however, yields the dinuclear Mn(III)–Mn(III) complex cation [(L-Me 2) 2Mn 2(O)(OOCC 6H 5) 2] 2+ ( 2), isolated also as the hexafluorophosphate salt.In the case of sodium acetate, both cations, the Mn(III)–Mn(IV) complex [(L-Me 2) 2Mn 2(O) 2(OOCCH 3)] 2+ ( 3) and the known Mn(III)–Mn(III) complex [(L-Me 2) 2Mn 2(O)(OOCCH 3) 2] 2+ ( 4) are available, depending upon the molar ratio.The single-crystal X-ray structure analyses show for the green crystals of [ 1][PF 6] 1.5[Cl] 0.5 · 1.5 H 2O and [ 3][PF 6] 2 · (CH 3) 2CO, a Mn–Mn distance of 2.620(2) and 2.628(4) Å, respectively, while for the red-violet crystal of [ 4][PF 6] 2, a Mn–Mn distance of 3.1416(8) Å is observed.All four compounds show catalytic activity for the oxidation of isopropanol with hydrogen peroxide in water and in acetonitrile to give acetone in the presence of oxalic or ascorbic acid as co-catalysts.