Synthesis of Open-Shell, Bimetallic Mn/Fe Trinuclear Clusters

Concomitant deprotonation and metalation of hexadentate ligand platform tbsLH6 (tbsLH6 = 1,3,5-C6H9(NHC6H4-o-NHSiMe2tBu)3) with divalent transition metal starting materials Fe2(Mes)4 (Mes = mesityl) or Mn3(Mes)6 in the presence of tetrahydrofuran (THF) resulted in isolation of homotrinuclear complexes (tbsL)­Fe3(THF) and (tbsL)­Mn3(THF), respectively. In the absence of coordinating solvent (THF), the deprotonation and metalation exclusively afforded dinuclear complexes of the type (tbsLH2)­M2 (M = Fe or Mn). The resulting dinuclear species were utilized as synthons to prepare bimetallic trinuclear clusters. Treatment of (tbsLH2)­Fe2 complex with divalent Mn source (Mn2(N­(SiMe3)2)4) afforded the bimetallic complex (tbsL)­Fe2Mn­(THF), which established the ability of hexamine ligand tbsLH6 to support mixed metal clusters. The substitutional homogeneity of (tbsL)­Fe2Mn­(THF) was determined by 1H NMR, 57Fe Mössbauer, and X-ray fluorescence. Anomalous scattering measurements were critical for the unambiguous assignment of the trinuclear core composition. Heating a solution of (tbsLH2)­Mn2 with a stoichiometric amount of Fe2(Mes)4 (0.5 mol equiv) affords a mixture of both (tbsL)­Mn2Fe­(THF) and (tbsL)­Fe2Mn­(THF) as a result of the thermodynamic preference for heavier metal substitution within the hexa-anilido ligand framework. These results demonstrate for the first time the assembly of mixed metal cluster synthesis in an unbiased ligand platform.