Ruthenium complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane for atom and group transfer reactions

With support by macrocyclic tertiary amine ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3tacn), a number of mononuclear metal–ligand multiple bonded complexes have been isolated. Starting with a brief summary of these complexes, the present review focuses on ruthenium-oxo and -imido complexes of Me3tacn. A family of monooxoruthenium(IV) complexes [RuIV(Me3tacn)O(N–N)]2+ (N–N = 2,2′-bipyridines) and a cis-dioxoruthenium(VI) complex cis-[RuVI(Me3tacn)O2(CF3CO2)]+ have been isolated, and the structures of [RuIV(Me3tacn)O(bpy)](ClO4)2 (bpy = 2,2′-bipyridine) and cis-[RuVI(Me3tacn)O2(CF3CO2)]ClO4 have been determined by X-ray crystallography. Oxidation of [RuIII(Me3tacn)(NHTs)2(OH)] (Ts = p-toluenesulfonyl) with Ag+ and electrochemical oxidation of [RuIII(Me3tacn)(H2L)](ClO4)2 (H3L = α-(1-amino-1-methylethyl)-2-pyridinemethanol) are likely to generate ruthenium-imido complexes supported by Me3tacn. DFT calculations on cis-[RuVI(Me3tacn)O2(CF3CO2)]+ and proposed ruthenium-imido complexes have been performed. Complexes [RuIV(Me3tacn)O(N–N)]2+ are reactive toward alkene epoxidation, and cis-[RuVI(Me3tacn)O2(CF3CO2)]+ efficiently oxidizes various organic substrates including concerted [3+2] cycloaddition reactions with alkynes and alkenes to selectively afford α,β-diketones, cis-diols, or CC bond cleavage products. Related oxidation reactions catalyzed by ruthenium Me3tacn complexes include epoxidation of alkenes, cis-dihydroxylation of alkenes, oxidation of alkanes, alcohols, aldehydes, and arenes, and oxidative cleavage of CC, CC, and C–C bonds, all of which exhibit high selectivity. Ruthenium Me3tacn complexes are also active catalysts for amination of saturated C–H bonds.