Reactivity studies on [Cp′MnX(thf)]2: manganese amide and polyhydride synthesis

The sterically encumbered 1,2,4-(Me3C)3C5H2 (Cp′) ligand allows the synthesis of stable high spin mono(cyclopentadienyl) manganese complexes [Cp′MnX(thf)]2 (X = Cl, Br, I; 1-X). Thermal stabilities of 1-X toward ligand redistribution to [Cp2′Mn] (2) and MnX2 depend on the bridging halide ligand. The kinetic stability of 1-I in solution even at elevated temperatures is noteworthy. Complexes 1 are useful starting materials for further functionalizations. Metathesis of 1-Cl with [LiN(SiMe3)2(OEt2)]2 yields the 13 valence-electron (VE) complex, [Cp′MnN(SiMe3)2] (3), while the manganese polyhydride cluster, [{Cp′Mn}4{MnH6}], was formed in the reaction of 1-I and KHBEt3. The 17 VE [MnH6]4− core of 4 is effectively shielded by four high spin [Cp′Mn]+ units. Magnetic susceptibility studies on 4 suggest weak electron exchange coupling between the spin carriers, but the spin state of the central [MnH6]4− fragment remained ambiguous. Therefore, the electronic structure of 4 was also analyzed by broken symmetry (BS) DFT calculations, which provided strong evidence for a low spin [MnH6]4− unit in agreement with previous spectrochemical studies performed on [FeH6]4−.