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

The reaction of 1,4-dimethyl-1,4,7-triazacyclononane (L-Me2) with MnCl2 · 4H2O in acetonitrile gives, in the presence of sodium formate, hydrogen peroxide, triethylamine and KPF6, the dinuclear Mn(III)–Mn(IV) complex cation [(L-Me2)2Mn2(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-Me2)2Mn2(O)(OOCC6H5)2]2+ (2), isolated also as the hexafluorophosphate salt.In the case of sodium acetate, both cations, the Mn(III)–Mn(IV) complex [(L-Me2)2Mn2(O)2(OOCCH3)]2+ (3) and the known Mn(III)–Mn(III) complex [(L-Me2)2Mn2(O)(OOCCH3)2]2+ (4) are available, depending upon the molar ratio.The single-crystal X-ray structure analyses show for the green crystals of [1][PF6]1.5[Cl]0.5 · 1.5 H2O and [3][PF6]2 · (CH3)2CO, a Mn–Mn distance of 2.620(2) and 2.628(4) Å, respectively, while for the red-violet crystal of [4][PF6]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.

The reaction of 1,4-dimethyl-1,4,7-triazacyclononane (L-Me2) with MnCl2 · 4H2O in acetonitrile gives, in the presence of the corresponding carboxylato derivative, hydrogen peroxide, triethylamine and KPF6, the dinuclear Mn–Mn cations [(L-Me2)2Mn2(O)2(OOCH)]2+, [(L-Me2)2Mn2(O)(OOCC6H5)2]2+, [(L-Me2)2Mn2(O)2(OOCCH3)]2+ and [(L-Me2)2Mn2(O)(OOCCH3)2]2+.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.Figure optionsDownload as PowerPoint slide