Bis[(trimethylsilyl)methyl]manganese: Structural Variations of Its Solvent-Free and TMEDA-, Pyridine-, and Dioxane-Complexed Forms

First synthesized in 1976 and recently taking on a new significance as a key precursor to heterobimetallic alkali-metal−manganese(II) complexes, bis[(trimethylsilyl)methyl]manganese has been structurally characterized by X-ray crystallography. It forms a polymeric chain structure of formula [{Mn(CH2SiMe3)2}∞], 1, in which distorted tetrahedral, spiro Mn atoms are linked together via μ2-bonding alkyl ligands. The structure is notable for displaying two distinct categories of Mn−C bond lengths with a mean size differential of 0.225 Å and for being the first fully crystallographically characterized polymeric manganese(II) dialkyl compound. Magnetic measurements of 1 indicate a surprisingly strong spin exchange coupling of J ≈ −45 cm−1 between the manganese ions aligned along the chain. Four Lewis base complexes of bis[(trimethylsilyl)methyl]manganese have also been subjected to X-ray crystallographic studies. Previously known [TMEDA·Mn(CH2SiMe3)2], 2, and [(pyridine)2Mn(CH2SiMe3)2], 3, both adopt a simple monomeric arrangement with C2N2 distorted tetrahedral coordinations of the metal atom. Synthesized by direct addition of the Lewis base to 1, two further, new complexes, [{(dioxane)[Mn(CH2SiMe3)2]2}∞], 4, and [{(dioxane)[Mn(CH2SiMe3)2]}∞], 5, are also reported. Hemisolvate 4 displays dimeric [(Me3SiCH2)Mn(μ-CH2SiMe3)2Mn(CH2SiMe3)] subunits, whereas 1:1 solvate 5 consists of monomeric subunits of [{Mn(CH2SiMe3)2}∞]; in both cases these subunits are linked together via O(CH2CH2)2O bridges to generate one-dimensional polymers.