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

Abstract

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⁻.