Synthesis, reactivity, and solid state structures of four-coordinate iron(II) and manganese(II) alkyl complexes

Synthesis and characterization of new, four-coordinate, high-spin iron(II) and manganese(II) complexes of the general form L2MR2 (L-2 = neutral chelating ligand, R = alkyl) are described. Alkylation of the (x-diimine complex, [ArN=C(Me)-C(Me)=NAr]FeCl2 (Ar = 2,6-diisopropylphenyl), as well as the enantiopure iron dichloride compounds, (-)-(sparteine)-FeCl2 and (S)-((t)BuBox)FeCl2 ((S)-((t)BuBox) = 2,2-bis [2-[4(S)-(R')-1,3 -oxazolinyl] propane), with LiCH2SiMe3 afforded the corresponding dialkyl derivatives. Solution magnetic susceptibility measurements and X-ray diffraction studies reveal each of the new iron(II) bis-trimethylsilylmethyl complexes to be high-spin, S = 2, tetrahedral molecules. In addition (-)(sparteine)Fe(CH2CMe3)(2), (-)-(sparteine)Fe(CH2C6H5)(2), and (S)-((t)BuBox)Fe(CH2C6H5)(2) were also prepared and characterized by NMR spectroscopy and elemental analysis. An enantiopure, high-spin, tetrahedral manganese(II) dialkyl complex, (-)-(sparteine)Mn(CH2SiMe3)(2), has also been synthesized. The catalytic activity of the new iron complexes in carbon-carbon bond forming processes has been evaluated, and stoichiometric reactions of the dialkyls with olefins, carbon monoxide, and the Lewis acid B(C6F5)(3) have been examined.