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 (L2 = neutral chelating ligand, R = alkyl) are described. Alkylation of the α-diimine complex, ArNC(Me)−C(Me)NArFeCl2 (Ar = 2,6-diisopropylphenyl), as well as the enantiopure iron dichloride compounds, (−)-(sparteine)FeCl2 and (S)-(tBuBox)FeCl2 ((S)-(tBuBox) = 2,2-bis2-[4(S)-(R‘)-1,3-oxazolinylpropane), 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)-(tBuBox)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.