Dinuclear iron, ruthenium and cobalt complexes containing 1,4-dimethyl-1,4,7-triazacyclononane ligands as well as carboxylato and oxo or hydroxo bridges

Abstract

The reaction of 1,4-dimethyl-1,4,7-triazacyclononane (L–Me 2) with FeSO 4 · 7H 2O in aqueous ethanol gives, in the presence of sodium carboxylates, hydrogen peroxide, sodium hydroxide and KPF 6, the dinuclear Fe(III)–Fe(III) complex cations [(L–Me 2) 2Fe 2(O)(OOCR) 2] 2+ (R = H: 1, R = CH 3: 2, R = C 6H 5: 3), which crystallise as the hexafluorophosphate salts. The corresponding reaction with RuCl 3 · nH 2O does not work, however, the analogous Ru(III)–Ru(III) complex [(L–Me 2) 2Ru 2(O)(OOCCH 3) 2] 2+ ( 5) can be synthesised by reacting Ru(dmso) 4Cl 2 with L–Me 2, HCl and air in refluxing ethanol, followed by addition of sodium acetate, the mononuclear intermediate (L–Me 2)RuCl 3 · H 2O ( 4) being also isolated and characterised. The reaction of L–Me 2, sodium acetate, hydrogen peroxide and triethylamine with CoCl 2 · 6H 2O in acetonitrile yields, however, the hydroxo-bridged Co(III)–Co(III) complex [(L–Me 2) 2Co 2(OH)(OOCCH 3) 2] 3+ ( 6). The molecular structures of 2, 5 and 6, solved by single-crystal X-ray structure analyses of the hexafluorophosphate salts, reveal for the orange crystals of [ 2][PF 6] 2 a Fe–Fe distance of 3.104(1) Å, for the purple crystals of [ 5][PF 6] 2 a Ru–Ru distance of 3.230(1) Å, and for the violet crystals of [ 6][PF 6] 3 · (CH 3) 2CO a Co–Co distance of 3.358(1) Å. All six complexes show catalytic activity for the oxidation of isopropanol with hydrogen peroxide in water to give acetone in the presence of ascorbic acid as co-catalyst.