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.