Synthesis, Molecular Structure, and Catalytic Potential of the Tetrairon Complex [Fe4(N3O2-L)4(?-O)2]4+ (L = 1-Carboxymethyl-4,7-dimethyl-1,4,7-triazacyclononane)

The reaction of Fe sulfate with 1-carboxymethyl-4,7-dimethyl-1,4,7-triazacyclononane (L) and H2O2 in aq. EtOH gives a brown dinuclear complex considered to be [Fe2(N3O-L)2(?-O)(?-OOCCH3)]+ (1), which converts upon standing in MeCN soln. into the green tetranuclear complex [Fe4(N3O2-L)4(?-O)2]4+ (2). A single-crystal x-ray structure anal. of [2][PF6]4·5MeCN reveals 2 to contain four Fe(III) centers, each of which is coordinated to three N atoms of a triazacyclononane ligand and is bridged by one oxo and two carboxylato bridges, a structural feature known from the active center of methane monooxygenase. Accordingly, 2 was found to catalyze the oxidative functionalization of methane with H2O2 in aq. soln. to give MeOH, Me hydroperoxide, and formic acid; the total turnover nos. attain 24 catalytic cycles within 4 h. To gain more insight into the catalytic process, the catalytic potential of 2 was also studied for the oxidn. of higher alkanes, cycloalkanes, and iso-PrOH in MeCN, as well as in aq. soln. The bond selectivities of the oxidn. of linear and branched alkanes suggest a ferroxy radical pathway. [on SciFinder(R)]